Summary of climate science research (September 2018) 

by Diane Shisk

This is a survey of relatively recent scientific studies (and articles and books based on studies) addressing the issues of how fast the Earth is warming due to greenhouse gas emissions, the impact of that warming on “tipping points,”[1] what must be done to avoid dangerous warming and certain “tipping points,” and the impact that would result from various warming scenarios. All to brief us on our strategy for action by Co-Counselors and whether we should sound a louder alarm in the Communities on this topic. (Note that there are so many studies on these topics today that the studies done just since 2014 exceed the number done before then.[2])

My short summary of the data below is that it is too late to keep warming to 1.5°C (we will probably be there within a decade or so), and probably too late to keep it to 2°C (we will probably hit that by 2050), but that by acting very quickly to drastically cut carbon emissions now (peak by 2020 and halve emissions every decade thereafter), maximize natural carbon sinks, and successfully implement new technology (as yet unproven), we can possibly bring warming down to 1.5 – 2% by the end of the century (and keep reducing it until we do bring it down to 1.5°C or lower) unless certain tipping points are crossed.

But that level of commitment to action is not yet being demonstrated in many places and certainly not in the U.S. Failure to act quickly (or triggering of some tipping points no matter how fast we act) would result in at least a 3 - 4°C increase by the end of the century, at which point critical tipping points will almost certainly be crossed, with irreversible effects and huge loss of lives (hundreds of millions/billions of people in the next century) or even rendering the planet uninhabitable.

Note that while the data in the last ten years has pretty clearly demonstrated that the climate is warming more than expected, there are quite a few variables that make it difficult to predict future warming very precisely. These include differences in approaches and timeframes, different estimates of how much warming has happened to date, the impact of global aerosol cooling (see below), and difficulties in predicting “tipping points.”

Introduction from James Hansen (2015) (who has predicted the kind of impacts we’re seeing for the last 30 years)

“Humanity is rapidly extracting and burning fossil fuels without full understanding of the consequences. Current assessments place emphasis on practical effects such as increasing extremes of heat waves, droughts, heavy rainfall, floods, and encroaching seas (IPCC, 2014; USNCA, 2014). These assessments and our recent study (Hansen et al., 2013a) conclude that there is an urgency to slow carbon dioxide (CO2) emissions, because the longevity of the carbon in the climate system (Archer, 2005) and persistence of the induced warming (Solomon et al., 2010) may lock in unavoidable highly undesirable consequences.

Despite these warnings, global CO2 emissions continue to increase as fossil fuels remain the primary energy source. The argument is made that it is economically and morally responsible to continue fossil fuel use for the sake of raising living standards, with expectation that humanity can adapt to climate change and find ways to minimize effects via advanced technologies.

We suggest that this viewpoint fails to appreciate the nature of the threat posed by ice sheet instability and sea level rise. If the ocean continues to accumulate heat and increase melting of marine-terminating ice shelves of Antarctica and Greenland, a point will be reached at which it is impossible to avoid large scale ice sheet disintegration with sea level rise of at least several meters. The economic and social cost of losing functionality of all coastal cities is practically incalculable. We suggest that a strategic approach relying on adaptation to such consequences is unacceptable to most of humanity, so it is important to understand this threat as soon as possible.”[3]

The news in the past few months points to more and more signs that global warming is progressing quickly (more details below). A very recent study (August 2018) argues that social and technological trends and decisions occurring over the next decade or two could significantly influence the trajectory of the Earth System for tens to hundreds of thousands of years and potentially lead to conditions that resemble planetary states that were last seen several millions of years ago, conditions that would be inhospitable to current human societies and to many other contemporary species.[4] 

United Nations International Panel on Climate Change

The International Panel on Climate Change (IPCC) targets that were agreed upon at COP21 in Paris (2015) were: to limit global warming to “well below 2°C,” and make all efforts to limit it to 1.5°C, acknowledging that with 2°C warming some very harmful effects will occur. In 2014 the IPCC stated we must cut carbon pollution sharply starting now or risk “severe, pervasive and irreversible impacts for people and ecosystems.”[5] Climate policymaking is significantly shaped by the work of the IPCC.

The IPCC has laid out estimates of how much CO2 we can emit and still limit global average temperature rise to no more than 1.5°C, 2°C, or 3°C above pre-industrial levels (using 1870 as the base year). These are known as carbon budgets. For each temperature limit there are three budgets, each corresponding to a different probability of staying below that limit: 66%, 50%, and 33%.[6] See attached 2017 IPCC Carbon Budget.

The UN acknowledges that voluntary national emission reduction commitments made in support of the Paris agreement put the world on a path of 3.4°C of warming by 2100 and more than 5°C if high-end risks including carbon-cycle feedbacks are taken into account. (The book Six Degrees says business as usual gets us to 3°C by 2050.)

However, the IPCC has been criticized as tending toward reticence and caution, downplaying more extreme and damaging outcomes. Actual climate changes keep ending up at the high end of their estimates or above. While their conservatism is understandable because of the pressure exerted by political and vested interests, some think it is becoming dangerously misleading given the acceleration of climate impacts globally. What were lower-probability, higher-impact events are now becoming more likely. An Environmental Research Letters study found “The rate of sea-level rise in the past decades is greater than projected by the …IPCC,” rising 60% faster.[7]

Other key attributes of global warming have also been under-predicted. (For example, the IPCC figures don’t take tipping points into account, ignoring major studies predicting significant impact. Several tipping points have likely been passed at 1°C of warming, [see below].)

An April 2018 survey by Carbon Brief of numerous studies about the remaining carbon budget before 1.5°C is reached conclude that the IPCC’s models have underestimated the remaining carbon budget, that sizeable differences between the studies still remain, and that it is hard to pin down a number to use as the remaining allowable emissions. One expert notes that the notion of a carbon budget may not be very useful for strict emissions targets like 1.5°C because “the rise in global temperatures is already close enough to 1.5°C that small differences in calculations have a big impact.”[8]

In 2017, the UN warned: “The concentration of carbon dioxide in the atmosphere increased at record speed last year to hit a level not seen for more than three million years” according to The Greenhouse Gas Bulletin, the UN weather agency’s annual flagship report.[9] This report “has raised alarm among scientists and prompted calls for nations to consider more drastic emissions reductions at the upcoming climate negotiations in Bonn. The authors urged policymakers to step up countermeasures to reduce the risk of global warming exceeding the Paris climate target of between 1.5°C and 2°C.  The gap between international goals and domestic commitments leaves the world on course for warming well beyond the 2°C target and probably beyond 3°C.”[10] 

A new report from the IPCC on the feasibility of attaining the 1.5°C goal is due out in October 2018.[11] The IPCC has recently circulated the Final Draft of the report to governments, with a request for comments on the Summary for Policymakers.[12] It is cited throughout this piece as “IPCC 2018 Draft Report.”

Global Climate Action Summit, September 2018

A document called the “Exponential Climate Action Roadmap” was submitted to the Global Climate Action Summit in California, September 2018. It states “The Paris Agreement’s goal to reduce the risk of dangerous climate change can be achieved if greenhouse gas emissions peak by 2020, halve by 2030 and then halve again by 2040 and 2050. This is now technologically feasible and economically

attractive but the world is not on this path.”[13] The report also states: Delaying action increases the humanitarian and economic cost and makes climate stabilization more difficult. Every five-year delay before emissions peak could result in an additional 20 centimeter (7.9 inch) rise in sea-level in the future. Around 90% of urban areas lie on coasts and vulnerable deltas. Climate change is increasingly an existential threat to low-lying island states and many coastal populations. Infrastructure built between now and 2030 will largely determine whether the world can limit warming to well below 2°C.[14] 

Greenhouse gas emissions

In 2013, the IPCC concluded that all of the warming since 1970 is due to human causes.[15] The primary GHG is CO2, accounting for 82% of the increase in warming over the last decade (2017 report). The rate of increase of CO2 is increasing: “the record increase of 3.3 ppm in CO2 from 2015 to 2016 was larger than the previous record increase, observed from 2012 to 2013, and the average growth rate over the last decade.” Atmospheric CO2 reached 145% of the pre-industrial level in 2016, primarily because of emissions from combustion of fossil fuels and from cement production, deforestation and other land-use change. That same year methane (CH4) contributed 17% of warming; nitrous oxide (NO2) 6%.[16] Black carbon is also a major pollutant.[17] Of the total emissions from human activities during the period 2006–2015, about 44% accumulated in the atmosphere, 26% in the ocean and 30% on land.[18]

Ice core records from Antarctica provide proof that over the past eight swings between ice ages (glacials) and warm periods similar to today (interglacials), atmospheric CO2 varied between 180 and 280 ppm, demonstrating that today’s CO2 concentration of ~400 ppm exceeds the natural variability seen over hundreds of thousands of years.



Global warming is currently happening at a rate of .16°C per decade. Because the warming effects of CO2 take decades to accumulate, we have not yet started to feel the impact of much of the carbon we’ve already emitted. This time lag makes it hard to appreciate how serious the problem already is. Methane, on the other hand, has a warming potential far greater than CO2, but stays in the atmosphere only 12 years.[19] Climate change that is taking place because of increases in CO2 concentration is largely irreversible (though in a short time frame, drawdown of CO2 from the atmosphere can reduce warming) for 1000s of years after emissions stop.[20] Stopping methane emissions, on the other hand, stops temperature rise very quickly.

Anthropogenic GHG emissions are mainly driven by population size, economic activity, lifestyle, energy use, land use patterns, technology, and climate policy. The Representative Concentration Pathways (RCPs)(possible future scenarios), which are used for making projections based on these factors, describe four different 21st century pathways of GHG emissions and atmospheric concentrations. The RCPs include a stringent mitigation scenario (RCP2.6 where warming is restricted to below 2°C), two intermediate scenarios (RCP4.5 where warming reaches 2-3°C and RCP6.0 where warming reaches 2.6-3.7C) and one scenario with very high GHG emissions (“business as usual)(RCP8.5 where warming reaches 4-6°C). Scenarios without additional efforts to constrain emissions (’baseline scenarios’) lead to pathways ranging between RCP6.0 and RCP8.5.[21] Note that these figures talk about a global average, and warming of 2°C in one location could mean a 12°C elsewhere. 

The Arctic region is warming at a rate twice that of the global average. Even if global temperature stabilized at 2°C, that would mean a likely 5°C increase for the Arctic region.[22]


The impact of methane emissions is not included in the IPCC estimates, or many studies. A recent study shows that the US oil and gas supply chain emits about 13 million metric tons of methane, the main component of natural gas, every year. That's much higher than the US Environmental Protection Agency's (EPA's) estimate of about 8 million metric tons.

Methane warms the planet 80 times as much as CO2 over the first 20 years after it is released. Scientists estimate that the methane in the atmosphere contributes about 25% of global warming. If left unchecked methane emissions from the oil and gas industry could erode the potential climate benefits of using natural gas, which releases far less carbon dioxide and other toxic pollutants than coal when it is burned. One study says these numbers are too low because they used faulty instruments and didn’t include leakage from gas distribution systems.[23] (See more on Howarth below, under 1.5°C.)

All climate forcers need to be tackled aggressively: CO2 to stop temperatures from rising and to limit long-term warming beyond this century, and short-lived climate forcers (SLCF), including methane, nitrate, black carbon, hydroflourocarbons, particulates, and aerosols to limit near-term warming. Reducing SLCFs could avoid up to 0.6C warming by mid-century; this is about half of the projected CO2 warming until then.[24]

Agricultural land use

While most human-caused CO2 emissions (80%) result from burning fossil fuels (coal, oil, gas), other significant sources are industrial agriculture and deforestation (20%).[25] Agricultural land use continues to expand because of dietary changes and population growth, causing harm to ecosystems through deforestation as well as emissions. Production of animal products dominates agricultural land use change, accounting for 65% over the last 50 years. Use for bioenergy contributed 36% to agricultural expansion.[26]


If the cement industry were a country, it would be the third largest emitter in the world. In 2015, it generated around 2.8 billion tons of CO2, equivalent to 8% of the global total—a greater share than any country other than China or the US. Cement use is set to rise as global urbanization and economic development increases demand for new buildings and infrastructure. Along with other parts of the global economy, the cement industry will need to dramatically cut its emissions to meet the Paris Agreement’s temperature goals. However, only limited progress has been made so far.[27]

Climate Change in the Past

The world’s climate has changed before many times, but human-caused climate change is different from previous natural climate changes. First, it is much faster by orders of magnitude. Second, it is happening in a context of tremendous habitat fragmentation and already-damaged natural systems due to destructive agricultural and settlement practices. Third, we now have a global civilization brimming with vulnerable people, farms, and infrastructure.

The last time it was 6 degrees warmer was 55 million years ago—when there were rainforests in Greenland. At that time, the “Earth was free of ice, and sea level was 70 meters (230 feet) higher on average than it is today.”[28] It was also 6 degrees warmer than today during the great Permian extinction 251 million years ago.[29] 

The last time the Earth’s atmosphere was at 400ppm of CO2 was a few million years ago. The climate was 2 - 3°C above preindustrial temperatures and sea level was some 10-20 meters (33 – 66 feet) above modern levels.[30] A 2009 analysis in Science found that when CO2 levels were approximately 400ppm (15 – 20 million years ago) the Earth was 5 to 10°F warmer and seas were 75 to 120 feet higher.[31] 

James Hansen says paleoclimate data are essential for understanding the major climate feedbacks. Processes of special importance are: (1) the role of the Southern Ocean in ventilating the deep ocean, affecting CO2 control of global temperature, and (2) the role of subsurface ocean warming in ice shelf melt, affecting ice sheet disintegration and sea level rise.[32] (More about ocean currents and climate change later.)


There was widespread consensus in 2016 that to have a 50-66% chance to limit global temperature rise to 1.5°C: 1. global emissions must peak by 2020 then decline, 2. the world must “decarbonize” by 2040-2060, 3. there must be net negative carbon emissions from 2050 onwards, and 4. biosphere resilience must be enhanced.[33] The “IPCC 2018 Draft Report” says that this is now out of reach and “there is very high risk that global warming will exceed 1.5°C.” Speaking about the IPCC 2018 Draft Report a researcher in climate extremes at the University of Melbourne, says “The reality is that staying under the 1.5°C threshold is now nigh-on impossible. Meeting the 1.5°C target now means overshooting and coming back down using negative emissions.[34] Achieving the goal of less than 1.5 °C warming will require carbon intensity to decline much faster than in the recent past.[35] 

The global mean temperature reached 1°C around 2017/2018, but one quarter of the Earth’s population lives in regions that already experience annual mean temperature increase of at least 1.5°C in at least one season. The rise in extreme temperatures in some regions can be 4.5°C.[36] The report predicts we will reach 1.5°C by the 2040s.

From 2013 to 2016, there were three consecutive years with very small emissions growth, but emissions climbed 1.7% to 32.5 gigatons in 2017,[37] as the world’s energy consumption increased 2.2% (demand for crude oil grew by 1.7 million barrels a day in 2018, while percentage of renewable energy remained at 4%).[38] As of the start of 2017, we have just over 4 years left of our carbon budget to not exceed 1.5°C warming. We will run out in 2021 if we continue emissions at the 2016 level.[39]

Some researchers (Howarth team) think there is some chance to stay below 1.5°C if we drastically reduce both methane and CO2 emissions immediately.[40] But that would require drastically reducing fracking of natural gas, which seems unlikely. (G20 countries are projected to see investments of over USD 1.6 trillion in gas production in this period. This is a major threat to climate action because these projects will lock in GHG emissions that massively exceed the Paris goals.)[41] 

Global warming will exceed 1.5°C by 2026 for RCP8.5 and 2030 for RCP4.5.[42] (A slow-moving oscillation in the climate system, the Interdecadal Pacific Oscillation, will impact the rate at which we reach 1.5°C, plus or minus 5 years.)[43]

A May 2018 article in Vox says “most current 2- or 1.5-degree scenarios show: Global carbon emissions rise in the short term, then plunge rapidly to become net negative around 2060, with gigatons of carbon subsequently captured and buried over the remainder of the century.” To reduce emissions so severely we will need to (1) radically increase energy efficiency (best if efficiency outruns growth—electricity, transportation, buildings, and industry, all with the most efficient available materials and technologies, everywhere in the world, starting immediately); (2) radically increase renewable energy (primarily wind and solar); (3) electrify everything, especially vehicles, home heating and cooling, and lower-temperature industrial applications. And we will probably still need negative emissions as well.[44]

The book Drawdown calls for aggressive transformation of electricity generation, transportation, buildings and cities, agriculture, land use, food demand, materials, rights for women and girls, ecosystem restoration and protection in its top ten solutions.[45]


The latest analysis shows that a level of 450 ppm is enough to melt a significant portion of the world’s ice, because feedback mechanisms kick in; melting ice hastens the melting of even more ice, for example, and thawing permafrost emits methane that accelerates warming, prompting permafrost to thaw even more.[46] 

A 2018 study titled “Trajectories of the Earth System in the Anthropocene” concluded that if humans cause the earth's global average temperature to increase by a further 1°C, the world could face a "hothouse" climate and trigger further warming—even when all human emissions cease. It found the Earth was heading for a tipping point, known as a "hothouse" climate, which could lead to average temperatures up to 5°C higher than pre-industrial temperatures and rises in sea level of between 10 and 60 meters (33 and 197 feet).[47] The report to the Global Climate Action Summit cites this study and lays out a comprehensive Roadmap to stay within the 2°C of warming.

The IPCC 2018 Draft Report notes higher risks associated with all climate change impacts by the additional .5°C of warming. Staying below 2°C will also be a daunting undertaking. The Paris Agreement voluntary emission reduction commitments, if implemented, would result in the planet warming by at least 3°C, without taking into account “long-term” carbon-cycle feedbacks. With a higher climate sensitivity figure of 4.5°C, for example, which would account for such feedbacks, the Paris path would lead to around 5°C of warming, according to a MIT study. A study by Schroder Investment Management published in June 2017 found—after taking into account indicators across a wide range of the political, financial, energy and regulatory sectors—the average temperature increase implied across all sectors was 4.1°C.[48]

In fact, the optimistic emission scenarios associated with the Paris goal show that warming will “overshoot” the 1.5°C target by up to half a degree, before cooling back to it by the end of this century. Those scenarios rely unduly on unproven Bio-Energy with Carbon Capture and Storage (BECCS) technology in the second half of the century, because the Paris Agreement does not assume steep emissions reductions will happen immediately.[49]

The likely range of global temperature increase is 2.0 – 4.9 °C, with median 3.2 °C and a 5% (1%) chance that it will be less than 2°C (1.5 °C).[50] There is a 50% probability of 2.4 - 2.6 °C warming in the near term (2050) and 4.1 – 5 °C warming by 2100.[51] And, a temperature rise of 2°C would lead to anything from 2.6 to 6.6°C warming in the Arctic by 2050, with the speed of transition between .5 and 1.5 °C per decade.[52]

“The constraint posed by the near-term (next three decades) risk of dangerous (50% probability) to catastrophic (5% probability) warming is that emission of CO2 and short-lived climate pollutants (SLCPs) should peak immediately and bend downward by 2020. A no-regret policy will be to undertake both CO2-dedicated and SLCP-dedicated measures simultaneously.[53]

The “Exponential Climate Action Roadmap,” finds that while the Paris Agreement’s goal to reduce the risk of dangerous climate change could be achieved if greenhouse gas emissions peak by 2020, halve by 2030 and then halve again by 2040 and 2050, the world is not on this path. Failure to meet these targets could potentially lead to a “Hothouse Earth” state.[54] 

James Hansen concludes that “the modeling, paleoclimate evidence, and ongoing observations together imply that 2°C global warming above the preindustrial level could be dangerous. Continued high fossil fuel emissions this century are predicted to yield (1) cooling of the Southern Ocean, especially in the Western Hemisphere; (2) slowing of the Southern Ocean overturning circulation, warming of the ice shelves, and growing ice sheet mass loss; (3) slowdown and eventual shutdown of the Atlantic overturning circulation with cooling of the North Atlantic region; (4) increasingly powerful storms; and (5) nonlinearly growing sea level rise, reaching several meters over a timescale of 50 – 150 years. These predictions, especially the cooling in the Southern Ocean and North Atlantic with markedly reduced warming or even cooling in Europe, differ fundamentally from existing climate change assessments.”[55]

Above 2°C and Sea Level Rise

James Hansen in 2011: “Humanity faces near certainty of eventual sea level rise of at least 5 – 9 meters, if fossil fuel emissions continue on a business-as-usual course, e.g., IPCC scenario A1B (balanced between renewable and fossil fuel) that has CO2 ∼ 700 ppm in 2100. Sea level rise sets the lowest limit on allowable human-made climate forcing and CO2, because of the extreme sensitivity of sea level to ocean warming and the devastating economic and humanitarian impacts of a multi-meter sea level rise. Doubling times (of pre-industrial CO2 levels) of 10, 20 or 40 years yield sea level rise of several meters in 50, 100 or 200 years. Recent ice sheet melt rates have a doubling time near the lower end of the 10 – 40 year range. We conclude that 2°C global warming above the preindustrial level, which would spur more ice shelf melt, is highly dangerous.”[56]

Tipping Points and “Point of No Return”

The American Association for the Advancement of Science writes, “Pushing global temperatures past certain thresholds could trigger abrupt, unpredictable and potentially irreversible changes that have massively disruptive and large-scale impacts. At that point, even if we do not add any additional CO2 to the atmosphere, potentially unstoppable processes are set in motion.”[57]

Tipping points are points at which positive feedback loops would trigger additional warming. For example, when Arctic sea ice melts, we’re left with more ocean water whose darkness absorbs more of the sun’s heat, therefore contributing to warming. This has caused the Arctic region to warm at twice the rate of the planet as a whole.[58]

Theoretically we could reach such a tipping point without triggering this kind of feedback loop if the excess atmospheric carbon was removed quickly enough. A point of no return, which is harder to pinpoint than a tipping point, is the level at which these feedback results are irreversible.[59] Currently, we have already crossed some global tipping points and could be on the way to a point of no return. 

The figure below shows a global map of some potential tipping “cascades,” divided into three clusters based on their estimated threshold temperature. Cascades could occur when a rise in global temperature reaches the level of the lower-temperature cluster, activating tipping elements, such as loss of the Greenland Ice Sheet or Arctic sea ice. These tipping elements, along with some of the nontipping element feedbacks (e.g., gradual weakening of carbon sinks), could push the global average temperature even higher, inducing tipping in mid- and higher-temperature clusters. For example, tipping (loss) of the Greenland Ice Sheet could trigger a critical transition in the Atlantic Meridional Ocean Circulation (AMOC), which could together, by causing sea-level rise and Southern Ocean heat accumulation, accelerate ice loss from the East Antarctic Ice Sheet on timescales of centuries.[60]



Antarctica and Greenland

The Greenland ice cap and Antarctic ice are beginning to melt. In 2012, a team from NASA and the European Space Agency put together satellite data to produce the most comprehensive assessment to date of ice sheet loss, showing that the Greenland ice sheet saw nearly a five-fold increase in melt rate between the mid-1990s and 2011. In 2014 they found Greenland had doubled its rate of ice loss since 2009.[61]   Greenland alone contains enough ice to raise the sea level by 7 meters. Some scientists think this will happen once the global temperature rise hits 1.2°C, which happened in May 2018 by some reports.

Two studies from 2014 find that some Western Antarctic ice sheet glaciers “have passed the point of no return… The collapse of this sector of West Antarctica appears to be unstoppable.”[62] Two June 2018 studies published in Nature show (1) that the rate of melting from the Antarctic ice sheet has accelerated threefold in the last five years and is now vanishing faster than at any previously recorded time, and (2) that unless urgent action is taken in the next decade the melting ice could contribute more than 25 cm to a total global sea level rise of more than a meter by 2070. This could eventually lead to the collapse of the entire west Antarctic ice sheet and another 3.5 meter of sea-level rise.[63] The IPCC 2018 Draft Report states that “thresholds for irreversible, multi-millennial loss of the Greenland and West Antarctic ice sheets may occur at 1.5 or 2°C global warming.

Complete melting will probably take centuries or millennia, although James Hansen warns we could be facing “explosively rapid” melting and sea rise. He asserts that business-as-usual emissions will almost certainly result in multi-meter sea-level rise by 2100, due in part to subsurface warming of the Antarctic ice sheet.[64] The IPCC predicts a much more comfortable .25 to 1 meter rise for this century.[65] Whether it happens this century or not, melting of Greenland ice from a 1.2°C temperature rise would flood Miami, Manhattan, London, Bangkok, Mumbai, and Shanghai. Half of humanity would have to relocate.

Sea-level rise is essentially irreversible once begun. At temperatures above 2°C, the great ice sheets of both Greenland and east Antarctica will eventually melt. Their contributions will raise sea level by 25 meters. The last time the planet was 4°C warmer the poles were ice-free. 

“Here, using a fully coupled model, we show … that the Greenland ice sheet is more sensitive to long-term climate change than previously thought. We estimate that the warming threshold leading to a mono-stable, essentially ice-free state, is in the range of 0.8 – 3.2°C, with a best estimate of 1.6°C. By testing the ice sheet’s ability to regrow after partial mass loss, we find that at least one intermediate equilibrium state is possible, though for sufficiently high initial temperature anomalies, total loss of the ice sheet becomes irreversible. Crossing the threshold alone does not imply rapid melting (for temperatures near the threshold, complete melting takes tens of millennia). However, the timescale of melt depends strongly on the magnitude and duration of the temperature overshoot above this critical threshold.”[66]

Also with present growth of freshwater injection from Greenland, in combination with increasing North Atlantic precipitation, we already may be on the verge of substantial North Atlantic climate disruption.[67]

Ocean circulation

The Atlantic Meridional Overturning Circulation, or AMOC, is a global conveyor belt of water, critical to the world’s climate and fisheries (moving warm water and nutrients around the planet). Warm water from the Gulf of Mexico flows northeast, it gradually cools, and in cooling, compresses and sinks. Eventually, in the Labrador and Greenland Seas, it becomes dense enough that it plunges down thousands of meters into the deep ocean. There it becomes a new current, running back south. It can remain in this deep-ocean current for many years until it eventually upwells at the equator or in the Southern Ocean.

A strong AMOC seems to shape the planet’s climate systems. It moderates the intensity of Atlantic hurricanes, lessens the risk of drought in North America, and assures the health of monsoons in India. AMOC also ferries warm weather from the equator to Western Europe, where it helps bring the region unusually mild winters.

Crucially, the entire AMOC system depends on cool, dense water “overturning” in the northwest Atlantic Ocean. Without cooled water plunging into the deep ocean near Greenland, and turning back south, the entire conveyor belt will stop. The “paleoclimatic record” shows that the AMOC has rapidly collapsed in the past. A Hansen 2016 study postulated that the melting of the Greenland ice sheet would dump enough cold fresh water into the AMOC to shut it down.

Then, a 2017 study showed how a popularly used climate model significantly overestimated the stability of AMOC and that it could collapse under the pressures of global warming and higher ocean temperatures, with or without the melting of Greenland.[68] 

In recent years, new sensors show the AMOC has been “sluggish,” “at it’s weakest state in centuries,”[69] causing concerns for greater flooding, more extreme weather, and disruption of fisheries.

Vegetation and Soil Sinks

Many climate tipping points are related to vast carbon sinks, or natural stores of ancient carbon. When temperatures rise, some of these sinks start to give off their carbon, dramatically speeding up the process of climate change. At 2°C degrees an estimated 15% of vegetation and soils may start to off-gas their carbon, becoming a net contribution to climate change instead of a bulwark against it. This may increase to 40% at 4°C.[70] Sinks also harbor points of no return. At 4°C, carbon-rich Arctic soils could thaw, resulting in vast emissions, perhaps 900 billion tons are stored there today. And, sometime in the 22nd century, we may see the release of vast amounts of carbon stored as methane hydrates at the bottom of the sea.[71]

A December 2011 article in Nature, “Climate Change: High Risk of Permafrost Thaw,” surveyed 41 international experts, called the Permafrost Carbon Network, who are public on permafrost issues. They concluded: “Our collective estimate is that carbon will be released more quickly than models suggest, and at levels that are cause for serious concern.” They project as much as 380 billion metric tons of CO2 equivalent will be released by 2100. They calculate that the defrosting permafrost will release roughly the same amount of carbon as current rates of deforestation would release. However, “because these emissions include significant quantities of methane, the overall effect on climate could be 2.5 times larger.”

A global temperature rise of 1.5°C would be enough to start the melting of permafrost in Siberia, though the melting would take decades.[72]

An April 2017 Nature Climate Change study, “An Observation-Based Constraint on Permafrost Loss as a Function of Global Warming,” found that every 1°C of additional warming would thaw one quarter of the earth’s frozen tundra area—releasing staggering amounts of GHG.

In yet another climate change feedback loop, recent droughts caused plants to reduce their CO2 uptake by 15%, apparently as part of their mechanism to conserve water.[73]    

Land and ocean sinks

CO2 emissions are stabilizing in recent years (although rising again) while concentration in the atmosphere is still increasing—leading to speculation that there is slower uptake by ocean/land, i.e. saturation of natural carbon sinks. Other studies found the land/ocean sink rate had decreased by a factor of 1/3 between 1959 and 2012, potentially adding another 1°C of warming by 2100.[74]


Over 90% of the heat from human caused warming ends up in the ocean, mostly in the near surface waters. This drives ocean stratification, decreasing mixing between the upper ocean and the intermediate and deep ocean. This limits uptake of GHG emissions that models speculate will result in a drop of CO2 uptake by 2100 of up to 30%.[75]

Negative Emissions

“We will need negative emissions (removal of CO2 from the atmosphere) on a large-scale and for a long period of time to bring global temperatures back down to 1.5°C. This isn’t possible with current technologies.”[76] Negative emissions are almost certainly required though their feasibility uncertain. But relying less on removal requires precipitous emission reductions (which are not happening).[77] It also requires ethical evaluation of the impacts of these technologies, but there has been no systematic evaluation of the ethics of carbon removal methods by the climate assessment community or professional philosophers.[78]

It will require newly created CO2 sinks (equivalent to the size of the oceans) in additional to preserving natural carbon and methane sinks (e.g. forests, mangroves, peatlands, soil). There is rising scientific evidence that biosphere resilience on land and in the ocean is rather uncertain and potentially even deteriorating.[79]

The primary instrument has been assumed to be BECCS: bioenergy (burning plants to generate electricity) with carbon capture and sequestration. The hypothetical idea is that plants absorb carbon as they grow; when we burn them, we can capture and bury that carbon. The result is electricity generated as carbon is removed from the cycle—net-negative carbon electricity. There is considerable opposition to BECCS because of extreme land use requirements (taking land out of food production as the need for food is increasing).

Also, using large-scale BECCS to limit warming to 2°C could require up to 18% of the land surface to be converted to biomass plantations, which could pose a significant threat to biodiversity.[80] 

Mitigation scenarios that achieve the ambitious targets included in the Paris Agreement typically rely on greenhouse gas reductions combined with net carbon dioxide removal (CDR) from the atmosphere, mostly accomplished through large-scale application of BECCS and afforestation. However, CDR strategies face several difficulties such as reliance on underground CO2 storage and competition for land with food production and biodiversity protection. The question arises whether alternative deep mitigation pathways exist such as lifestyle change, additional reduction of non-CO2 GGH, and more rapid electrification of energy demand based on renewable energy. Although these alternatives also face specific difficulties, they are found to significantly reduce the need for CDR, but not fully eliminate it. The alternatives offer a means to diversify transition pathways to meet the Paris Agreement targets, while simultaneously benefiting other sustainability goals.[81]

New technologies are finding ways to store carbon. A new study has found storing billions of ton of CO2 underground would be a safe and effective way to help limit the effects of climate change. The research uses a new model to look at what would happen if 12 billion tons of CO2 were injected under the ground and left for 10,000 years. It finds the risk of CO2 leakage would be minimal.[82] Cost and how quickly it could be brought online are not addressed.

The Drawdown model shows emission reductions goals can be reached without BECCS.[83] For example, bio-sequestration in agricultural land and natural ecosystems; with very modest biochar use (but note at high enough levels of warming this stored carbon can be re-emitted to atmosphere; these are considered "temporary and non-permanent" by IPCC).

Global Aerosol Cooling (from Climate Mobilization) 

The earth’s overheating has been partially counteracted by the effect of short-lived atmospheric aerosol particles, tiny particles suspended in the atmosphere that are released through industrial, agricultural, construction, and transportation processes (including aviation). Aerosols are also released in natural processes such as volcanoes and forest fires.

Some aerosols, such as black carbon soot, have a short-term warming effect, while others, such as sulfates, have a short-term cooling effect (they are also pollutants). Other aerosols include organic carbon, nitrates, and dust from smoke, manufacturing and windstorms. Overall, aerosols are directly and indirectly cooling the earth by an unknown amount (due to insufficient monitoring). Estimates range from approximately 0.5°C – 1.2°C.

Fossil fuel burning is the source of about 72% of sulfate aerosol emissions, the primary cause of the global net aerosol cooling. The aerosol effect is known as “global dimming” or “solar dimming,” since cumulative aerosol emissions collectively reflect an increasing amount of sunlight back into space and increase cloud cover. The aerosols are generally washed out of the atmosphere by rain after about 10 days, but are continually replenished due to human activities.

If global fossil fuel combustion is rapidly eliminated, as it must be in order to counteract the global warming emergency and extreme ocean acidification, the earth will experience a surge of global warming. It seems theoretically possible to counteract the heating surge with either one or a combination of the following approaches, which vary dramatically in risk levels and feasibility:

  • Simultaneous, drastic cuts in short-lived warming agents (methane, black carbon, hydrofluorocarbons, and ground level-ozone)
  • The simultaneous sequestration (removal) of globally significant quantities of greenhouse gases at an extreme speed far beyond any rate currently considered feasible by leading experts
  • A combination of drastic cuts in short-lived warming agents supplemented by tremendously fast global greenhouse gas sequestration
  • The use of solar radiation management cooling interventions (such as shooting aerosols into the stratosphere) to cool the planet or limit the warming surge.

(Note: This plan does NOT call for the use of any solar radiation management technologies or methods)

Former NASA climate scientist James Hansen has described the aerosol cooling predicament as humanity’s “Faustian bargain.”[84] The aerosol cooling dilemma is a sub-set of the larger global air pollution emergency. Sulfate aerosols are one type of a series of air pollutants that collectively kill some 6.5 – 7 million people prematurely every year through heart disease, stroke, chronic obstructive pulmonary disease (COPD), lung cancer, and acute lower respiratory infections in children, according to the World Health Organization.

Economics of 1.5 - 2°C

Over the next 15 years, the world will require about $90 trillion in new infrastructure, most of it in developing and middle income countries. The International Energy Agency that limiting the rise in global temperature to below 2 Celsius by the end of the century will require an average of $3.5 trillion a year in energy sector investments until 2050.[85] 

It is also important to note that limiting global temperatures to 1.5°C is expected to have economic advantages. One paper published earlier this year found per capita GDP would be 5% higher by 2100 if temperatures are stabilized at 1.5°C rather than 2°C.[86]

The World Bank has noted that the human and economic costs of natural disasters have been underestimated by up to 60 percent. One estimate is that we’ll soon need to provide $300 billion a year to compensate for the losses due to climate change.[87]

Projected Impacts of Climate Change

The risks to human societies through impacts on health, livelihood, food and water security, human security, and infrastructure are higher at 1.5°C than they are today, and higher still at 2°C. IPCC 2018 Draft Report. Some people will suffer the consequences of climate change to a much greater degree than others. In a 2014 report the IPCC stated that “risks are unevenly distributed and are generally greater for disadvantaged people and communities in countries at all levels of development.”[88] 2°C would be disastrous for much of the world. African delegates at the UN climate summit in Copenhagen cried out “2°C is suicide” for their countries.[89] 

At 1.5°C the Arctic will be ice free in September.[90] (The ice is breaking up much faster than expected. Ice north of Greenland, once thought to be the last area of ice that would break up, broke up in the summer of 2018.)

Missing the 1.5°C limit and reaching 2°C of warming will mean a more palpable change in local temperatures in the tropics than at higher latitudes. As the less economically developed areas of the world tend to be in the tropics and the more developed economies are in the higher latitudes, we see a strong inverse relationship. This mean, in general, the wealthiest will experience less perceptible climate change than the poorest.[91]

The additional .5°C of warming increases risks from heat, water scarcity, storms, changes in precipitation, permafrost melting, ocean acidification, lost of land and ocean biodiversity, sea level rise, and so on.[92] One exception will be that warmer temperatures in the temperate zone will create more ideal conditions for agricultural pests, and so their numbers, energy level, and consumption will grow by about 10-25% for each 1°C of temperature rise. In the tropics, the same pests are at their optimal working temperature, and the additional temperature increase will start limiting populations. [93]

Storm Impacts

The frequency of climate related disasters is projected to triple from 2009 to 2030. These events would impact 660 million people each year, mostly in less developed countries with less infrastructure. Storms that we have thought of as once in a century may come every 30 years by the 2050s and every 4 years in the 2080s and beyond.[94] A 1°C rise in global temperatures would increase the frequency of Katrina magnitude storm events by 3 to 4 times. A 2°C rise would mean Katrina magnitude storm surges 10 times more extreme, or one occurring every other year.[95] Climate change is intensifying El Niño effects (short term fluctuations in weather patterns).[96]

Some regions of the world are projected to become much drier, while others will become more humid. In humid regions, “all weather events are affected by climate change because the environment in which they occur is warmer and moister than it used to be.”[97] Because warmer air holds more moisture (4% increase for every 1°C of temperature increase), there will be not only more storms, but stronger storms.[98] The intensity index of storms has already doubled as ocean temperatures have risen. At 3°C hurricane intensity increases so much we may need to add a new category—Category 6—to reflect these new superstorms.[99] Storms will also affect regions that have not previously experienced them. (Brazil 2004, Ireland 2017.)

Rainfall will likely come in the form of intense storms, causing flash floods and poor infiltration.[100] At 1°C of warming, regions such as western North America will see stronger droughts.[101] Southern Africa will become drier, while northern Africa will become more humid, if only in the short term. “Super El Niño” effects could bring an end to the Indian monsoon rains, which provide critical rainfall for billions of people.[102] And the Sahara desert would move north into Southern Europe.[103] Meanwhile other regions of the world will see excessive rainfall and flash flooding.

Considerable research also indicates that we are seeing more atmospheric blocking patterns that can keep major weather patterns stuck for extended periods of time. And all future storms will be operating in areas with increasingly higher sea levels, so storm surges will get worse and worse.[104]

Species extinction

The IPCC reports that up to 30 percent of species are at increasing risk of extinction at 1°C. Above 2°C there is a “moderate” chance that the Amazon will dry up and become a desert resulting in a tremendous loss of biodiversity, store carbon, and land inhabited by indigenous people. At 3°C, 33 to 50 percent of all living species will be on their way to extinction.[105] Between 10 and 50 percent of the world’s habitats will be gone. Another source finds that, in a future with relatively high amounts of global warming and land-use change, the number of animal species in the average ecosystem could fall by 38%, when compared to conditions from 1961-90.[106] (In part, this is because trees and plants are only able to shift their ranges by 200 kilometers a century.)[107]

Heat can kill the symbiotic algal partners of corals, a phenomenon known as coral bleaching. It takes 30 years to recover, but even with 1°C warming most corals will be bleached, and at 3°C the IPCC expects “widespread mortality” of corals.[108] (There is much substantiation of this.)

CO2 taken up by the oceans makes the water more acidic. At 2°C warming, parts of the Southern Ocean and Pacific will become toxic to organisms such as plankton, crabs, and shellfish that use calcium carbonate to make shells. The effect on plankton is especially worrisome, because they are critical to oceanic carbon sequestration (the ocean is the largest of our global carbon pools). Their loss could lead to the spread of “marine deserts” devoid of the base of their food chain.[109]

Beavers have been reported in the Yukon tundra for first time as the ‘shrubification’ of the Arctic draws herbivore species further north.[110] In Colombia, butterflies and flowers are migrating up mountains in search of a climactic refuge.[111]

Sea level rise

The National Climate Assessment, a November 2017 (congressionally mandated and approved by the White House) report by scientists from 13 U.S. government agencies predicts a rate of 1 foot of sea level rise per decade after 2050 and 2 feet per decade after 2100. Rate of sea level rise is hugely dependent on rate of melting of Greenland and Antarctic ice, as noted above, and could reach several meters by 2100.

Agricultural Impacts

Food prices are project to rise by as much as 84% this century.[112] Declines of agricultural productivity of 15 to 30 percent are projected by 2080 in Africa, South Asian, and Central America.[113]

While it is possible at 1 - 2°C to shift to other crops, changing the staple food of whole regions and countries is difficult. While wealthy people can “buy” food security, poor families and countries will be hit hard by climate change.[114]

Sea level rise will result in increased salinization of rivers in coastal regions, leading to shortages of drinking and irrigation water.

“Here we develop a new data set of more than 1,700 published simulations to evaluate yield impacts of climate change and adaptation. Without adaptation, losses in aggregate production are expected for wheat, rice and maize in both temperate and tropical regions by 2°C of local warming. Crop-level adaptations increase simulated yields by an average of 7–15%, with adaptations more effective for wheat and rice than maize. Yield losses are greater in magnitude for the second half of the century than for the first. Consensus on yield decreases in the second half of the century is stronger in tropical than temperate regions, yet even moderate warming may reduce temperate crop yields in many locations.[115] The International Rice Research Institute reports that grain (rice, wheat, maize) yields are predicted to decrease by 10% for every degree increase over 30°C. Many areas in the tropics are close to the 30°C threshold.

A recent paper addresses how much larger are the impacts of climate change on food security at 2°C compared to 1.5°C world. The figure below is their “Hunger and Climate Variability Index,” shown for a 2°C warmer world, looking at predicted rainfall and drought (not sea level rise or other factors). The image is scaled according to how vulnerable countries are to food insecurity. Countries with a larger value are more vulnerable than countries with a smaller number. Any country with a vulnerability greater than 1 is more vulnerable than any country today.



Global warming increases the conditions for wildfires in many regions of the world. When trees and vegetation burn, they not only stop being a carbon sink, they also release their carbon back into the atmosphere causing further warming, resulting in more wildfires. Sharp declines in summer rainfall could be a “primary driver” of the record-breaking wildfires ripping across the western US, research shows. The study finds that there have been “previously unnoted” declines in summer rainfall across close to a third of forests in the western US over the past four decades. These declines are “strongly correlated” with wildfire increases, the study shows.[116]

Northern boreal forests store 30% of all the carbon stored on land, and many rest on permafrost and peatland. Fires blacken the area above the permafrost, speeding up the defrosting and loss of soil carbon to the atmosphere. Most of the world’s wetlands are peat, which are drying out and will dry faster (from both atmospheric heat and lowering of the water table, as well as for conversion to crop land) as the world warms. Peatlands store 25% of the earth’s soil carbon.[117] “Smouldering peat fires already are the largest fires on Earth in terms of their carbon footprint.”[118] By the end of the century, Arctic burning is likely to quadruple, according to a study in Environmental Research Letters.[119]

Heat Waves

A 2°C warming would double the land area subject to deadly heat and expose 48% of the population.[120] Heat related problems include heat-stroke, increase in urban smog, lack of access to water (and poor sanitation impacts) and malnutrition (caused by reduced nutrition from rising CO2 levels[121] as well as reduced food quantities from rising temperatures), changing patterns of infections and insect-borne diseases. Reduction in human productivity will also result as people are simply unable to work outside.

Recent studies indicate that heat waves may also pose a more significant threat than anticipated, rendering parts of the world uninhabitable by 2070 to 2100. North China, the Persian Gulf area, and South Asia are particularly at risk.[122] It also looks like we’re in for at least a meter of sea level rise by 2070.


Drought is caused by lower precipitation or higher temperatures (baking the land and leading to higher rates of evaporation) over an extended period of time. If a region gets hit by both, it will have an unusually extreme drought. As much as one third of the Earth’s currently habited and arable land faces a near-permanent drying this century.[123] Unless we reverse emissions trends soon, we risk having a situation by the 2060s where large swaths of the U.S., Brazil, Africa, the Mideast, Australia, Southeast Asia, and Europe are routinely in severe drought.[124]

As extremely dry conditions impact water availability, African nations are being urged to study the impact of drought on hydropower, questioning the wisdom of continuing to invest in major hydropower projects. The electricity security of whole regions of Africa is at risk.[125]

Access to water

The Proceedings of the National Academy of Sciences (2004) predict snowpack declines of between a third and three-quarters in a 2°C world. Air temperatures in the highlands regions are rising at twice the global average, accelerating glacial retreat. While river flows from the glaciers will initially increase (causing flooding), with the disappearance of snowpack and glaciers, water supplies will decrease up to 90%. Many communities globally are dependent on cyclical melting snowpack and glacial ice for year round water supply.[126]

Glaciers are already melting at rates not seen in more than 11,000 years. The loss of steady glacial melt-water would mean water shortages for one to two billion Chinese people this century.[127]

Other human impacts

At 2°C scientists anticipate 200 million refuges on the move annually by 2050.[128] A Cornell study predicts there could be 2 billion climate refugees by 2100.[129]

The IPCC warns, “Human security will be progressively threatened as the climate changes… Climate change is an important factor threatening human security through: (1) undermining livelihoods, (2) compromising culture and identity, (3) increasing migration that people would rather have avoided, and (4) challenging the ability of states to provide the conditions necessary for human security. Human rights to life, health, shelter and food are fundamentally breached by the impacts of climate change.[130]

Researchers estimate that at 2°C, climate change will endanger 2.7 billion people in 46 countries by fueling violent conflict.[131]

“The real horror of climate change isn’t that there’s something inherently monstrous about hurricanes, forest fires or sea level rise, but that the ways governments respond to them (or don’t) could be totally disastrous for a supermajority of the world’s population. Christian Parenti calls this the “politics of the armed lifeboat: the preparations for open-ended counterinsurgency, militarized borders, aggressive anti-immigrant policing and a mainstream proliferation of right-wing xenophobia.”[132]

Renewable Energy

In the United States, about 29 percent of global warming emissions come from our electricity sector. Most of those emissions come from fossil fuels like coal and natural gas. In contrast, most renewable energy sources produce little to no global warming emissions. Even when including “life cycle” emissions of clean energy (ie, the emissions from each stage of a technology’s life—manufacturing, installation, operation, decommissioning), the global warming emissions associated with renewable energy are minimal.

Renewable energy is providing affordable electricity across the country right now, and can help stabilize energy prices in the future. Although renewable facilities require upfront investments to build, they can then operate at very low cost (for most clean energy technologies, the “fuel” is free). As a result, renewable energy prices can be very stable over time.

Moreover, the costs of renewable energy technologies have declined steadily, and are projected to drop even more. For example, the average price to install solar dropped more than 70 percent between 2010 and 2017. The cost of generating electricity from wind dropped 66 percent between 2009 and 2016. Costs will likely decline even further as markets mature and companies increasingly take advantage of economies of scale. [133]

It’s Not Too Late

James Hansen writes: “If humanity wishes to preserve a planet similar to that on which civilization developed and to which life an Earth is adapted… CO2 will need to be reduced… to at most 350ppm, but likely less than that.” “An initial 350ppm target may be achievable by phasing out coal use, reducing GHG emissions 6% a year starting in 2012 (if we wait until 2020, must reduce CO2 by 15% a year),… and adopting agricultural and forestry practices that sequester carbon.”[134] These changes must be achieved in a few short decades in order to step back from tipping points and avoid catastrophic changes.[135] As of 2009, the total excess carbon dioxide in the atmosphere was 200 billion tons.[136]

Plans for Rapid Reductions in Emissions

Get the U.S. back in the Paris Agreement

The U.S. out of the Paris Agreement hinders initiatives in terms of meeting emissions goals and also solutions for carbon storage, reducing energy use, advancing renewables, and so on.

Exponential Climate Action Roadmap

Aiming to limit temperature rise to well below 2°C will require unprecedented action in four areas:

– Greenhouse gas emissions peaking by 2020 at the latest, and approximately halving every decade afterwards in a trajectory known as the Global Carbon Law. This translates to around a 7% reduction per year. Many companies can reduce emissions significantly faster.

– Farming and other land use must stop expanding and adopt solutions to store carbon rather than emit it.

– Large-scale reforestation and forest, wetland and peatland management to protect the resilience of these vital systems.

– Develop and scale robust solutions for storing carbon safely.

Necessary for emissions to turn down after 2020, from Three Years to Safeguard Our Planet. By 2020, we must achieve the following:[137]

Energy. Renewables make up at least 30% of the world’s electricity supply—up from 23.7% in 2015. No coal-fired power plants are approved beyond 2020, and all existing ones are being retired.

Infrastructure. Cities and states have initiated action plans to fully decarbonize buildings and infrastructures by 2050, with funding of $300 billion annually. Cities are upgrading at least 3% of their building stock to zero- or near-zero emissions structures each year.

Transport. Electric vehicles make up at least 15% of new car sales globally, a major increase from the almost 1% market share that battery-powered and plug-in hybrid vehicles now claim. Also required are commitments for a doubling of mass-transit utilization in cities, a 20% increase in fuel efficiencies for heavy-duty vehicles, and a 20% decrease in greenhouse-gas emissions from aviation per kilometer traveled.

Land. Land-use policies are enacted that reduce forest destruction and shift to reforestation and afforestation efforts. Current net emissions from deforestation and land-use changes form about 12% of the global total. If these can be cut to zero next decade, and afforestation and reforestation can instead be used to create a carbon sink by 2030, it will help to push total net global emissions to zero, while supporting water supplies and other benefits. Sustainable agricultural practices can reduce emissions and increase CO2 sequestration in healthy, well-managed soils.

Industry. Heavy industry is developing and publishing plans for increasing efficiencies and cutting emissions, with a goal of halving emissions well before 2050. Carbon-intensive industries—such as iron and steel, cement, chemicals, and oil and gas—currently emit more than one-fifth of the world’s CO2, excluding their electricity and heat demands.

Finance. The financial sector has rethought how it deploys capital and is mobilizing at least $1 trillion a year for climate action. Most will come from the private sector. Governments, private banks and lenders such as the World Bank need to issue many more ‘green bonds’ to finance climate-mitigation efforts. This would create an annual market that, by 2020, processes more than 10 times the $81 billion of bonds issued in 2016.


Book outlining “the 100 most substantive solutions to global warming: See PDF “Top 10 Solutions

Earth’s Future: The World’s Biggest Gamble

Guided especially by the latest scientific evidence about natural, economic, and societal nonlinearities, eight key requirements were formulated:

  1. Aim to keep global warming as far below 2°C as possible.
  2. Restrict cumulative carbon dioxide emissions to an overall carbon budget of less than one trillion tons after 2011, with net negative carbon emissions from 2050 onwards winding the cumulative emissions back well below one trillion tonnes of CO2.
  3. Phase‐out greenhouse gases completely by 2050 or shortly thereafter, through political measures such as carbon pricing and abolition of fossil‐fuel subsidies.
  4. An equitable sharing of the remaining global carbon budget, with developed nations decarbonizing well before 2050.
  5. Stimulate a wave of innovations, with a special emphasis on energy systems, transportation, and land use.
  6. Develop a global strategy to reduce vulnerability and build resilience to deal with loss and damage.
  7. Safeguard carbon sinks in the biosphere by maintaining ecosystems and critical biomes.
  8. Finally, secure $100 billion USD per annum in climate finance for developing countries.

The Climate Mobilization

Restore a Safe & Stable Climate

Overview. In order to restore a climate that is safe, stable, and supportive of human civilization, humanity must:

  • Drive the economy to net zero greenhouse gas emissions as rapidly as possible using emergency economic measures. The U.S. must reach net zero greenhouse gas emissions by no later than 2025, and the entire world community must reach net zero greenhouse gas emissions by no later than 2030.
  • Drastically slash annual global greenhouse gas emissions immediately. Indeed, global emissions must “drop off a cliff.”
  • Mount a large-scale carbon dioxide or greenhouse gas drawdown (or sequestration) effort immediately to restore pre-industrial greenhouse gas concentrations and cool the planet back to safe levels. Such an effort could take decades or even multiple centuries, depending on its scale and scope.
  • Calmly consider whether a near-term cooling of the planet is required to combat positive feedbacks such as thawing permafrost and dying tropical rainforest that could take global warming out of humanity’s control. If needed, figure out if

Reverse Overshoot

Overview. In order to reverse overshoot and stop the 6th mass extinction of species, humanity must:

  • Slow down and reverse global population growth.
  • Phase out consumerism and planned obsolescence.
  • Considerably shrink the physical resource consumption levels of the global economy, and drastically increase efficiencies of production.
  • Set aside at least half the Earth’s land surface and oceans for preservation.
  • Halt the further expansion of agricultural land and restore degraded lands.

See “The Victory Plan” for more:

 [1] Tipping points are points at which positive feedback loops would trigger additional warming.

[2] How can climate policy stay on top of a growing mountain of data?, The Guardian, June 2018,

[3] Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 ◦C global warming is highly dangerous,

[4] Steffen, et al., Trajectories of the Earth System in the Anthropocene. Proceedings of the National Academy of Sciences (2018),

[5] IPCC Synthesis Report, November 2014.

[6] The IPCC says global mean surface temperature change for the period 2016–2035 relative to 1986–2005 is similar for the four RCPs and will likely be in the range 0.3°C to 0.7°C (medium confidence). (Note that it has already surpassed 1°C since I started this paper in June 2018.) Relative to 1850–1900, global surface temperature change for the end of the 21st century (2081–2100) is projected to likely exceed 1.5°C for RCP4.5, RCP6.0 and RCP8.5 (high confidence). Warming is likely to exceed 2°C for RCP6.0 and RCP8.5 (high confidence), more likely than not to exceed 2°C for RCP4.5 (medium confidence), but unlikely to exceed 2°C for RCP2.6 (medium confidence). The increase of global mean surface temperature by the end of the 21st century (2081–2100) relative to 1986–2005 is likely to be 0.3°C to 1.7°C under RCP2.6, 1.1 - 2.6°C under RCP4.5, 1.4 - 3.1°C under RCP6.0 and 2.6 - 4.8°C under RCP8.5.

[7] What Lies Beneath,


[9] World Meterological Association, Greenhouse Gas Bulletin, October 2017

[10] Global atmospheric CO2 levels hit record high,

[11] IPCC Special Report: Global Warming of 1.5°C,

[12] Media report:

[13] Exponential Climate Action Roadmap ,

[14] Ibid. Executive Summary

[15] IPCC 5th Assessment report, September 2013

[16] World Meterological Association, Greenhouse Gas Bulletin, October 2017

[17] U.S.EPA. (2014) Greenhouse gas emissions

[18] World Meterological Association, Greenhouse Gas Bulletin, October 2017

[19] Romm, J., Climate Change: What everyone needs to know

[20] Solomon, S. et al. (2009). Irreversible climate change due to CO2 emissions. Proceedings of the National Academy of Sciences

[21] IPCC 2014, Climate Change Report, Synthesis report for policymakers, 8

[22] NOAA, Arctic Report Card, Update for 2017,

[23] Methane leaks from U.S. gas fields dwarf government estimates,, June 2018

[24] Earth’s Future, the World’s Biggest Gamble,

[25] Boden, T., G. Marland, and B. Andres, 2012: Global CO2 Emissions from Fossil-Fuel Burning, Cement Manufacture, and Gas Flaring: 1751-2009. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory,

[26] Drivers for global agricultural land use change: the nexus of diet, population, yield and bioenergy, Lund University Publications,

[27] Why cement emissions matter for climate change, September 13, 2018,

[28] Flannery, Now or Never, 34;

[29] Lynas, Six Degrees,

[30] World Meterological Association, Greenhouse Gas Bulletin, October 2017

[31] Romm, J. Climate Change: What everyone needs to know

[32] Hansen, Ice melt, sea level rise and superstorms,

[33] Earth’s Future, the World’s Biggest Gamble, Three Years to Safeguard Our Planet, Only 5 years left before 1.5 degree carbon budget is blown

[34] IPCC 2018 Special Report

[35] Less than 2C warming by 2100

[36] IPCC 2018 Draft Report,

[37] Global CO2 Emissions Rise after Paris Climate Agreement Signed, Scientific American, March 2018

[38] Energy and Climate Change, No Progress for 20 Years, (quoting from BP Statistical Review of World Energy 2018)

[39] Four years left 1.5C carbon budget

[40] Howarth video

[41] Debunked: The G20 Clean Gas Myth

[42] Climate Impact in Europe Under 1.5C Global Warming, (also in climatecodered)

[43] Trajectories toward the 1.5 degree target, Modulation by the Interdecadal Pacific Oscillation

[44] What Genuine No Bullshit ambition on climate change looks like,

[45] Hawkens, P., Drawdown, Top Ten Solutions

[46], December 2011

[47] Published in the Proceedings of the National Academy of Sciences (U.S.)

[48] What Lies Beneath,

[49] 1.5C of warming is closer than we imagine, just a decade away (April 2018); 2018 IPCC Draft Report

[50] Less than 2 °C warming by 2100 unlikely,

[51] Well below 2C: Mitigation strategies for avoiding dangerous to catastrophic climate changes

[52] Six Degrees

[53] Ibid.

[54] Steffen, et al., Trajectories of the Earth System in the Anthropocene. Proceedings of the National Academy of Sciences (2018),

[55] Hansen, J. Target Atmospheric CO2: Where Should Humanity Aim?

[56] Hansen, Ice Melt, 20119-21, 20061

[57] American Association for the Advancement of Science, “What We Know,”; Klein, This Changes Everything, 1

[58] Romm, J., Climate Change: What everyone needs to know; NOAA’s annual Arctic report card, December 12, 2017.

[59] Hansen,, “Target atmospheric CO2, Where should humanity aim?”

[60] Steffen, Trajectories of the Earth System.

[61] Romm, J., Climate Change: What everyone needs to know

[62] Rignot, E., 2014 study, NASA/UC Irvine, reported in Romm, J., Climate Change: What everyone needs to know

[63] Guardian, Antarctic ice melting faster than ever, studies show, June 13, 2018

[64] Hansen et al., “Ice melt, sea level rise and superstorms,”, 20119

[65] Lynas, 6 Degrees, 86-92

[66] Multistability and critical thresholds of the Greenland ice sheet,, March 2012

[67] Hansen, Ice Melt, 20120

[68] The Atlantic Ocean and an Actual Debate in Climate Science,, citing

[69] Scientific American, Slow-Motion Ocean: Atlantic’s Circulation Is Weakest in 1,600 Years,

[70] IPCC, Contribution of Working Group II, 16

[71] IPCC, Climate Change 2013, 70-71

[72] 1.5C rise in temperature enough to start permafrost melt, scientists warn,, study in Science Express

[73] Increased water-use efficiency and reduced CO2 uptake by plants during droughts at a continental scale,

[74] Howarth video; World Meteorological Organization (September 2014); Romm, J., Climate Change: What everyone needs to know

[75] Romm, J., Climate Change: What everyone needs to know

[76] IPCC 2018 Draft Report

[77] Earth’s Future, the World’s Biggest Gamble

[78] Don’t deploy negative emissions technologies without ethical analysis, Nature, September 19, 2018,

[79] Ibid.; Howarth video

[80] Climate change to become greatest pressure on biodiversity by 2070,, June 2018

[81] Alternative pathways to the 1.5C target reduce the need for BECCS

[82] Carbon Brief, World can ‘safely’ store billions of tonnes of CO2 underground,, June 2018

[83] Drawdown

[84] Hansen, Climate forcing growth rates; doubling down our Faustian bargain,” 2013 Environmental Research Letters,

[85] Climate Finance,

[86] Clean Energy investment must be 50% higher to limit warming to 1.5C,, June 2018

[87] Innovative finance needed to find $300 billion a year for climate losses, Thomas Reuters Foundation News,

[88] IPCC, Climate Change 2014: Impacts, Adaptation, and Vulnerability, 12; IPCC 2018 Draft Report

[89] Klein, “Why Black Lives Matter should transform the climate debate,” 1

[90] IPCC 2018 Draft Report,

[91] Exceeding 1.5 of global warming will hit poorest the hardest

[92] IPCC 2018 Draft Report

[93] Pests to eat more crops in warmer world, Science, August 2018

[94] Than, “Causes of California drought linked to climate change,” 1

[95] Proceedings of the National Academy of Sciences paper, “Projected Atlantic Hurricane Surge Threat from Rising Temperatures” (2013)

[96] Global warming is intensifying El Niño weather, Guardian, August 29, 2018

[97] Trenberth, K. Climatic Change, “How to Relate Climate Extremes to Climate Change”

[98] Tokar, Toward Climate Justice, 14

[99] Lynas, 6 Degrees, 66-67

[100] Lynas, 6 Degrees, 45

[101] Ibid. 30

[102] Than, “Causes of California drought linked to climate change,” 1

[103] Ibid.

[104] Romm, J., Climate Change: What everyone needs to know

[105] IPCC, Climate Change 2014, Mitigation of Climate Change, 178

[106] Carbon Brief, Biodiversity

[107] Six Degrees

[108] IPCC, Contribution of Working Group II, 16

[109] Lynas, 6 Degrees, 78

[110] Beavers reported on the Yukon tundra for the first time, Canadian Geographic, May 2917,

[111] Butterflies and flowers climb mountains in search of a climate refuge, EFE: Verde, May 2017,

[112] IPCC, Climate Change 2014: Impacts, Adaptation, and Vulnerability, 4

[113] Hoffman, “Agriculture at the Crossroads,” 3

[114] Hoffman, “Agriculture at the Crossroads,” 5

[115] A meta-analysis of crop yield under climate change and adaptation,, March 2014

[116] Summer rainfall declines ‘primary driver’ of surge in U.S. wildfires, Carbon Brief, August 2018,

[117] Science News, “Smoke Signals,” p. 20, March 2018

[118] Rein, G. Nature Geoscience, “Global Vulnerability of Peatlands to Fire and Carbon Loss,” 2015

[119] Science News, “Smoke Signals,” p. 24

[120] Well below 2C: Mitigation strategies for avoiding dangerous to catastrophic climate changes,



[123] Nature, “The Next Dust Bowl,” 2011

[124] National Center for Atmospheric Research, 2012, cited in Romm, J., Climate Change: What everyone needs to know

[125] Africa to suffer major blackouts as climate change dries up hydropower, scientists warn, The Independent, August 30, 2018

[126] Six Degrees

[127] Oxfam International, Suffering the Science, i-ii

[128] Ibid.

[129] Rising seas could result in 2 billion refugees by 2100, Cornell University,

[130] Anderson, “Climate change going beyond dangerous”

[131] Oxfam International, Suffering the Science, i-ii

[132] Why Abolishing ICE Is Good Climate Policy,

[133] Benefits of Renewable Energy Use, Union of Concerned Scientists, December 2017,

[134] Hansen,, “Target atmospheric CO2, Where should humanity aim?”; Hansen,

[135] Ibid.,16

[136] Flannery, Now or Never, 82

[137] Three years to safeguard our planet,

Last modified: 2019-05-02 14:41:35+00