Image: Yale Climate Connections
The Warming Rate for the Last Two Years Has Been 25 Times the Warming Rate of the Last 150 Years
A review of Hansen 2025.
In the last two years, Earth has warmed 0.4 degrees C, compared to 1.2 degrees C warming in the previous 100 years. This warming rate is 0.2 degrees C per year, compared with the previous 150 year’s warming rate of 0.008 degrees C per year. In other words, the warming rate of the last two years has been 25 times the warming rate of the previous 150 years. Half of this likely from loss of cooling sulfate aerosols from the reduction of sulfur in ship fuels mandated by new International Marine Organization’s (IMO) new regulations limiting sulfur in fuels, and the other half being from accelerated warming via increasing greenhouse gasses accumulated in our atmosphere and, failing Earth sinks that formerly absorbed greenhouse gases like our failing forests, oceans, permafrost, and ocean currents that bury heat and greenhouse gases absorbed by oceans. Some of this warming has been caused by our previous El Nino, but Hansen and team say not much.
It is good to see Hansen talking about direct cooling and carbon dioxide removal more and with greater emphasis. The IMO regulation-caused aerosol warming will last for generations and the acceleration of warming from degradation of Earth sinks and corresponding feedback emissions is extremely concerning. The paper screams for both emergency cooling and carbon dioxide removal, over and over again, but Hansen and team continues to focus on consensus reviews of the two that are biased low and lack details on both timelines and costs, and counterintuitive to the content of this lengthy paper, says they (the authors) are not supporting engineered solutions and carbon dioxide removal cannot get the job done. His reasoning mirrors challenges with published findings and proprietary processes concerning carbon dioxide removal, and with IPCC’s scenario bias, that are all understated because they are academic findings and or reviews. It also does not acknowledge the IRA’s IRS 45Q Carbon Sequestration Incentive’s contribution to implementation with no pay cap individually or cumulatively, and over 200, 1-million ton per year CO2 removal units committed under IRS 45Q already, that is a very robust start to implementing the carbon removal infrastructure required for climate restoration.
And a note on the illegitimate administration’s bent on climate destruction… They absolutely will not destroy IRS 45Q because this is literally unlimited revenues to removal entities, and trump tripled Obama’s original 45Q pay, with the IRA tripling trump’s tripling.
On engineered cooling solutions… Like Hansen says, we have been geoengineering our world for 200 years with greenhouse gases. So, how do we fix large complicated problems in our world today? With engineering of course. Is engineering dangerous? Generally, yes, but we have existing rules and regulations (or we once did…) that ensure we remain safe despite the dangers of engineered solutions to anything. I will put my seal on that.
Significance of IMO’s regulations… Hansen talks about aerosol cooling being an order of magnitude low with IPCC reviews and gives a lot of time to ship fuels. In other words, aerosol cooling from burning natural sulfur in fossil fuels is ten times greater than what IPCC suggests.
Aerosol cooling understated by ten times… One of the most important things I think the authors said beyond supporting, sort of, engineered solutions and carbon dioxide removal, is that stratospheric aerosols in pristine air over the oceans have a much greater cooling capacity than in polluted air over land. The reason is simple. In polluted air, where air pollution is far more predominant over land, this pollution includes dark aerosols, or dust and soot, that when struck by light energy, capture that light energy and warms, creating heat, where in the absence of these dark aerosols, the “bright aerosols,” or reflective aerosols like sulfates from burning sulfur in ship’s fuels, reflect light harmlessly back into space where it cannot strike something solid (like dark aerosols, or water, dirt, plants, etc., ) and turn into heat.
Another staggering conclusion of this paper is that shutdown of the AMOC, the Atlantic meridional overturning circulation, of which the Gulf Stream plays a major role, is likely to shut down by 2050.
If I had to cite one takeaway, it would be the quotation below from his Moral Hazard section.
“The environmental movement and academia have a huge responsibility in steering public debate on SRM, which they have largely shunned to date.”… “There is a need for analysis that compares the risks and benefits of purposeful global cooling scenarios against scenarios with no such cooling. This comparative risk analysis is typically absent in objections to SRM research; in a similar vein, proponents of SRM research should appreciate valid concerns about the moral hazard hypothesis and deal with it in a comparative “risks vs. risks” framework.”
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Hansen 2025 – review by Bruce Melton, Climate Change Now Initiative
Hansen et al., Global Warming Has Accelerated: Are the United Nations and the Public Well-Informed?, Environment, Science an Policy for Sustainable Dev, February 3, 2025.
https://www.tandfonline.com/doi/full/10.1080/00139157.2025.2434494
Global temperature spike 25 times greater than the previous 150 years… Global temperature leaped more than 0.4°C (0.7°F) during the past two years, the 12-month average peaking in August 2024 at +1.6°C relative to the temperature at the beginning of last century (the 1880-1920 average). This temperature jump was spurred by one of the periodic tropical El Niño warming events, but many Earth scientists were baffled by the magnitude of the global warming, which was twice as large as expected for the weak 2023-2024 El Niño.
Temperature response to shipping fuels sulfur regulations… “warming from the 2020 reduction of ship aerosols is one-third complete after five years; the next third requires a century and the final third requires millennia.
Tipping is real… “Tipping pointsFootnote92 are also real. Some feedbacks can pass a point such that the process accelerates and causes amplifying climate feedback. For example, global warming may melt Arctic permafrost, releasing large amounts of greenhouse gases to the atmosphere. Or heating and drying of the Amazon rainforest may reach a point that the rainforest is not self-sustaining, with fires releasing much of the carbon stored in the forest. Many tipping point processes are reversible if Earth cools, but the recovery time varies and may be long for some feedbacks.”
Restore our climate to the relatively stable Holocene… “Late Eemian climate also featured shutdown of the North Atlantic overturning circulation, as revealed by ocean cores of seafloor sediments.Footnote105 Shutdown of this ocean circulation short-circuits inter hemispheric transport of heat by the global ocean conveyor,Footnote106,Footnote107 which normally transports a huge amount of heat – 1,000 trillion watts – from the Southern Hemisphere into the Northern Hemisphere. That heat amounts to 4 W/m2 of energy averaged over the Northern Hemisphere, but it is mostly concentrated in the North Atlantic region, which is thus warmer than expected for its latitude. When the ocean conveyor shut down, that heat stayed in the Southern Ocean, where it may have contributed to collapse of the West Antarctic ice sheet. Meanwhile, in the North Atlantic region, there was evidence of powerful storms. This picture of the Eemian, if filled out in finer detailFootnote108 including the sequencing of events, may help us anticipate where our present climate is headed, if effective actions are not taken to halt and reverse human-made climate change, restoring relatively stable Holocene climate.”
Shutdown of AMOC by 2050… (abstract) “We find that polar ice melt and freshwater injection onto the North Atlantic Ocean exceed prior estimates and, because of accelerated global warming, the melt will increase. As a result, shutdown of the Atlantic Meridional Overturning Circulation (AMOC) is likely within the next 20-30 years, unless actions are taken to reduce global warming – in contradiction to conclusions of IPCC.”
“Our climate simulations led to the staggering conclusion that continued growth of ice melt will cause shutdown of the North Atlantic and Southern Ocean overturning circulations as early as midcentury and “nonlinearly growing sea level rise, reaching several meters in 50-150 years.” (authors emphasis, page 28)
Geoengineering recommended but, not … Hansen presents a powerful argument for geoengineering, very specifically stating that geoengineering and only geoengineering can avoid the point of no return. Yet, he purposefully states that in their section on Purposeful Global Cooling (below), “We do not recommend implementing climate interventions, but we suggest that young people not be prohibited from having knowledge of the potential and limitations of purposeful global cooling in their toolbox.”
Ship’s Fuels Forcing 10X Greater than IPCC… “Review41 of five ship aerosol modeling studies finds a range 0.07 to0.15 W/m2, with mean 0.12 ± 0.03 W/m2. A recent model result42 of 0.2 W/m2refers to ocean area and is thus a global forcing of 0.14 W/m2. None of these modeled Ship Aerosol Forcings would have much effect on global temperature because GHG forcing currently is increasing 0.4-0.5 W/m2 per decade. However, if the aerosol effect is highly nonlinear (i.e., if aerosols emitted into polluted air have much less effect on clouds than aerosols emitted into a pristine atmosphere), decreased ship emisions may have a large effect on Earth’s albedo (reflectivity). The largest effect should be in the North Pacific and North Atlantic, where ship emissions dominate over natural sulfate aerosols (Sidebar 5). Fortunately, Earth’s albedo has been monitored for almost a quarter of a century by the CERES (Clouds and the Earth’s Radiant Energy System) satellite instrument,44 which reveals a stunning darkening of Earth (Figure 6).45 Earth’s albedo decreased about 0.5%(of 340 W/m2), which is 1.7 W/m2 additional heating of Earth since 2010! Such albedo change is equivalent to an increase of CO2 by 138 ppm, from the 419 ppm actually measured at the beginning of 2024 to 557 ppm.”
“How can we reconcile our estimate of 0.5 W/m2 for ship aerosol forcing with the six aerosol modeling studies mentioned above,41,42 which are in mutual agreement that the global ship aerosol forcing is small, in the range 0.07-0.15W/m2? Let’s first summarize our alternative analysis of the aerosol forcing and then suggest an approach to resolve the large difference. Our initial estimate of the ship aerosol forcing was based on the precise CERES satellite data, calibrated absolutely with Argo float data.44,55 The CERES data show that Earth’s albedo (reflectivity) decreased 0.5% since 2010, corresponding to a 1.7 W/m2 global average increase of Absorbed Solar Radiation. Based on the spatial and temporal coincidence of the increased absorption with regions where the effect of ship aerosols should be largest –the North Pacific and North Atlantic –we infer a Ship Aerosol Forcing of ∼0.5W/m2, an order of magnitude larger than follows from the IPCC aerosol for-mulation.”
Purposeful Global Cooling Section
“Today’s older generations – despite having adequate information – failed to stem climate change or set the planet on a course to avoid growing climate disasters. And they tied one arm of young people behind their back by supporting only renewable energies as an alternative to fossil fuels. Now, as it has become clear that climate is driving hard toward the Point of No Return, there are efforts to tie the other arm of young people behind their back. We refer to efforts to prohibit actions that may be needed to affect Earth’s energy balance, temporarily, while the difficult task of reducing greenhouse gases is pursued as rapidly as practical – namely Solar Radiation Modification (SRM). Purposeful global cooling with such climate interventions is falsely described as “geoengineering,” while, in fact, it is action to reduce geoengineering. Human made climate forcings are already geoengineering the planet at an unprecedented, dangerous, rate.
We, the authors – who range in experience from young people just beginning our careers to older scientists who have spent half a century in research aimed at better understanding of Earth’s climate – are concerned about the danger of again “being too late” in informing the public about actions that may be needed to preserve the marvelous world we inherited from our parents. We do not recommend implementing climate interventions, but we suggest that young people not be prohibited from having knowledge of the potential and limitations of purposeful global cooling in their toolbox. We do not subscribe to the opinion that such knowledge will necessarily decrease public desire to slow and reverse growth of atmospheric greenhouse gases; on the contrary, knowledge of such research may increase public pressure to reduce greenhouse gas amounts.”
The Point of No Return… “The Point of No Return – The greatest climate threat is probably the danger of the West Antarctic ice sheet collapsing catastrophically.”
“The problem of West Antarctic ice sheet collapse is complicated because it may be related to – spurred by – shutdown of the North Atlantic overturning circulation, which is part of a global ocean conveyor that normally transports heat from the Southern Ocean into the Northern Hemisphere. When the North Atlantic Overturning circulation shuts down, that heat stays in the Southern Hemisphere where it can contribute to Antarctic ice melt.”
“Point of No Return research deserves greater attention than it has received. There is evidence that global climate models IPCC has relied on do not realistically represent the possibility of shutdown of the North Atlantic Overturning Circulation,1,96 nor do they simulate the rapid sea level changes that occur in the paleoclimate record.49 A more powerful research approach would give emphasis to paleoclimate analysis and to observations of ongoing climate changes at least comparable to global climate modeling.”
(Editor’s note: While I do agree that Antarctic collapse is mightily important, Hansen and team do not significantly acknowledge the global degradation of our other Earth’s systems, that does not self-restore as long as the temperature remains above the level which allowed the degradation to begin, and almost always results in nonlinearly increasing degradation even with a stable temperature, because of the positive feedbacks of heat in the environment. This is one of Hansen’s main justifications for climate restoration back to less than 1 degrees C warming above normal, that he repeats over and over again in his publications since 2007. This is the primary justification Sierra Club used to lower our warming target from 1.5 C to “less than 1 C.”)
Geoengineering to avoid the point of no return… “Sidebar 11. Ice shelves adhered to the Antarctic continent extend down the side of the continent to depths as great as 2 km in the Southern Ocean, where they provide the strongest buttressing force Footnote130 holding the ice sheet in place. Ice shelves are the “cork” that prevents rapid expulsion of Antarctic ice into the Southern Ocean – especially the vulnerable West Antarctic ice, which rests on bedrock below sea level. Footnote131 The rapid Eemian sea level rise likely was preceded by melting of Antarctic ice shelves. Today, ice shelves around Antarctica are again melting, with the melting accelerated by slowdown of the ocean overturning circulation. The overturning is driven by cold, salty water near the Antarctic coast that sinks to the ocean floor, compensated by rising, warmer water; this circulation is an escape valve for deep ocean heat. Global warming today is increasing ice melt around Antarctica, freshening and reducing the density of the upper ocean, thus reducing the overturning circulation Footnote49 and escape of ocean heat to space during the cold Antarctic winter. Based on a conservative estimate Footnote110 of observed ice melt in 2011 and a 10-year doubling time for the melt rate, a global climate model yields a 30% slowdown of the overturning circulation in 2025, Footnote132 consistent with observational data. Footnote133 Thus, today the ocean surface layer around Antarctica is freshening and cooling (Figure 3, Cheng et al.), Footnote134 but the ocean below is warming. Purposeful aerosol cooling recharges this overturning Antarctic circulation, allowing deep ocean heat to escape to the atmosphere and space and cooling the ocean at depth while warming much of the thin surface layer as the upwelling deep-ocean heat melts sea ice (Figure 24).”
IPCC Approach is insufficient… “the United Nations IPCC approach, heavily emphasizing global climate modeling, is insufficient.”
Carbon capture at the gigaton scale does not exist – Of course it doesn’t, we haven’t built it yet… “Carbon capture at the gigaton scale does not exist; the estimated annual cost of CO2 extraction is now $2.2-4.5 trillion dollars per year,116”
Carbon Capture Costs Four Times Reality at $2.2-4.5 trillion dollars per year – Reference 116… Hansen uses unrealistically high costs for carbon removal. Hansen’s assumption on removal costs are are in direct conflict with Keith 2018’s $94 ton with natural gas energy, interpreted for using renewable energy at $0.01 kWh at ~ $54 ton and much less with almost free natural gas energy to the provider.
…Reference 116 – “Assuming empirical cost estimates of 451-924 TnUS$/tC, based on a pilot direct-air CO2 capture plant. See J. Hansen, P. Kharecha, “Cost of carbon capture: Can young people bear the burden?” Joule2 (2018): 1405-7”
Here is Hansen’s error and the reason why he continues to insist that carbon capture costs are exorbitant. The above paper, Cost of Carbon Capture… assumes, “costs are often discussed in units of $/tC, where tC is tons of carbon. A ton of CO2 is 44/12 times heavier than a ton of C. Thus, the Keith study implies a removal cost of $451–$924/tC.” Keith 2018 definitively does not calculate his $94 ton removal cost as tons of carbon. He calculates it appropriately as tons CO2.
Geoengineering reverses fast feedbacks… Modeling understates fast feedback response to geoengineering… “Modeling limitations are why we suggest comparable emphasis on paleoclimate studies, climate modeling, and modern observations of ongoing changes. In the latter category, there is the global, natural experiment of cooling by stratospheric aerosols provided by the 1991 Pinatubo volcanic eruption, which spread aerosols into both hemispheres. The maximum negative forcing was about −3 W/m2, more than enough to offset Earth’s present energy imbalance of 1-1.5 W/m2 and cause global cooling. Such negative forcing, if maintained for years, would cause reversal of fast feedbacks, including regrowth of sea ice area. Major effects of the brief Pinatubo forcing included global cooling in the next two years that peaked at 0.3 °C and a 50% reductionFootnote138 in the growth rate of atmospheric CO2 that lasted about three years. Negative effects included a temporary reduction of stratospheric ozoneFootnote139 in the tropics and adverse changes of precipitation patterns.Footnote140”
Geoengineering fails at high GHG concentrations, but needed to prevent overshoot, and can reduce Antarctic ice loss and sea level rise… “high greenhouse gas scenario such as RCP8.5 creates such great warming and melting that aerosol intervention will almost surely be fruitless in the end. Our Figure 15 is a shocking revelation that real-world greenhouse gases are increasing at nearly the RCP8.5 rate. Policy must focus on reducing actual greenhouse gas emissions to a steeply declining growth rate relative to RCP8.5(Figure 15). Solar Radiation Modification (SRM) – whether via stratospheric aerosols or otherwise – should be considered only as a possibility to address temporary overshoot of safe global temperature while atmospheric greenhouse gases are reduced as rapidly as practical. With that caveat, numerous studies, e.g., 136,137 suggest that stratospheric aerosols have potential to reduce the risks of Antarctic ice loss and sea level rise.”
Greenhouse gas (carbon dioxide) removal indicated in the Purposeful Global Cooling section… “Solar Radiation Modification (SRM) – whether via stratospheric aerosols or otherwise – should be considered only as a possibility to address temporary overshoot of safe global temperature while atmospheric greenhouse gases are reduced as rapidly as practical.”
Purpopseful cooling actions… Hansen only says “purposeful cooling actions,” but both geoengineering and carbon removal are purposeful cooling actions. “The gap between reality and the growth rate required to keep global warming less than +2 °C is so great (see Figure 15) that it is now implausible to keep warming under that target without purposeful cooling actions, in additionto reducing greenhouse gas amounts.”
Moral hazard… “whether moral hazard plays out should depend on how SRM is framed, e.g. as a panacea or get-out-of-jail card vs. a complementary measure. SRM must be presented as an auxiliary tool that could help reverse some of the damage already set in motion by the fossil fuel industry and irresponsible politics. The environmental movement and academia have a huge responsibility in steering public debate on SRM, which they have largely shunned to date.”
“There is a need for analysis that compares the risks and benefits of purposeful global cooling scenarios against scenarios with no such cooling. This comparative risk analysis is typically absent in objections to SRM research; in a similar vein, proponents of SRM research should appreciate valid concerns about the moral hazard hypothesis and deal with it in a comparative “risks vs. risks” framework.”