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Science
Related: About this forumJames Hansen et al: Global Warming Has Accelerated: Are the United Nations and the Public Well-Informed?
https://doi.org/10.1080/00139157.2025.2434494Original Articles
Global Warming Has Accelerated: Are the United Nations and the Public Well-Informed?
James E. Hansen, Pushker Kharecha, Makiko Sato, George Tselioudis, Joseph Kelly, Susanne E. Bauer, Reto Ruedy,Eunbi Jeong,Qinjian Jin,Eric Rignot,Isabella Velicogna,Mark R. Schoeberl,Karina von Schuckmann,Joshua Amponsem,Junji Cao,Anton Keskinen,Jing Li &Anni Pokela
Pages 6-44 | Published online: 03 Feb 2025
https://doi.org/10.1080/00139157.2025.2434494
Abstract
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. We find that most of the other half of the warming was caused by a restriction on aerosol emissions by ships, which was imposed in 2020 by the International Maritime Organization to combat the effect of aerosol pollutants on human health. Aerosols are small particles that serve as cloud formation nuclei. Their most important effect is to increase the extent and brightness of clouds, which reflect sunlight and have a cooling effect on Earth. When aerosols and thus clouds are reduced, Earth is darker and absorbs more sunlight, thus enhancing global warming. Ships are the main aerosol source in the North Pacific and North Atlantic Oceans. We quantify the aerosol effect from the geographical distribution of sunlight reflected by Earth as measured by satellites, with the largest expected and observed effects in the North Pacific and North Atlantic Oceans. We find that aerosol cooling, and thus climate sensitivity, are understated in the best estimate of the United Nations Intergovernmental Panel on Climate Change (IPCC).
Global warming caused by reduced ship aerosols will not go away as tropical climate moves into its cool La Niña phase. Therefore, we expect that global temperature will not fall much below +1.5°C level, instead oscillating near or above that level for the next few years, which will help confirm our interpretation of the sudden global warming. High sea surface temperatures and increasing ocean hotspots will continue, with harmful effects on coral reefs and other ocean life. The largest practical effect on humans today is increase of the frequency and severity of climate extremes. More powerful tropical storms, tornadoes, and thunderstorms, and thus more extreme floods, are driven by high sea surface temperature and a warmer atmosphere that holds more water vapor. Higher global temperature also increases the intensity of heat waves and at the times and places of dry weather high temperature increases drought intensity, including flash droughts that develop rapidly, even in regions with adequate average rainfall.
Polar climate change has the greatest long-term effect on humanity, with impacts accelerated by the jump in global temperature. 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. If AMOC is allowed to shut down, it will lock in major problems including sea level rise of several meters thus, we describe AMOC shutdown as the point of no return.
We suggest that an alternative perspective a complement to the IPCC approach is needed to assess these issues and actions that are needed to avoid handing young people a dire situation that is out of their control. This alternative approach will make more use of ongoing observations to drive modeling and more use of paleoclimate to test modeling and test our understanding. As of today, the threats of AMOC shutdown and sea level rise are poorly understood, but better observations of polar ocean and ice changes in response to the present accelerated global warming have the potential to greatly improve our understanding.
Global Warming Has Accelerated: Are the United Nations and the Public Well-Informed?
James E. Hansen, Pushker Kharecha, Makiko Sato, George Tselioudis, Joseph Kelly, Susanne E. Bauer, Reto Ruedy,Eunbi Jeong,Qinjian Jin,Eric Rignot,Isabella Velicogna,Mark R. Schoeberl,Karina von Schuckmann,Joshua Amponsem,Junji Cao,Anton Keskinen,Jing Li &Anni Pokela
Pages 6-44 | Published online: 03 Feb 2025
https://doi.org/10.1080/00139157.2025.2434494
Abstract
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. We find that most of the other half of the warming was caused by a restriction on aerosol emissions by ships, which was imposed in 2020 by the International Maritime Organization to combat the effect of aerosol pollutants on human health. Aerosols are small particles that serve as cloud formation nuclei. Their most important effect is to increase the extent and brightness of clouds, which reflect sunlight and have a cooling effect on Earth. When aerosols and thus clouds are reduced, Earth is darker and absorbs more sunlight, thus enhancing global warming. Ships are the main aerosol source in the North Pacific and North Atlantic Oceans. We quantify the aerosol effect from the geographical distribution of sunlight reflected by Earth as measured by satellites, with the largest expected and observed effects in the North Pacific and North Atlantic Oceans. We find that aerosol cooling, and thus climate sensitivity, are understated in the best estimate of the United Nations Intergovernmental Panel on Climate Change (IPCC).
Global warming caused by reduced ship aerosols will not go away as tropical climate moves into its cool La Niña phase. Therefore, we expect that global temperature will not fall much below +1.5°C level, instead oscillating near or above that level for the next few years, which will help confirm our interpretation of the sudden global warming. High sea surface temperatures and increasing ocean hotspots will continue, with harmful effects on coral reefs and other ocean life. The largest practical effect on humans today is increase of the frequency and severity of climate extremes. More powerful tropical storms, tornadoes, and thunderstorms, and thus more extreme floods, are driven by high sea surface temperature and a warmer atmosphere that holds more water vapor. Higher global temperature also increases the intensity of heat waves and at the times and places of dry weather high temperature increases drought intensity, including flash droughts that develop rapidly, even in regions with adequate average rainfall.
Polar climate change has the greatest long-term effect on humanity, with impacts accelerated by the jump in global temperature. 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. If AMOC is allowed to shut down, it will lock in major problems including sea level rise of several meters thus, we describe AMOC shutdown as the point of no return.
We suggest that an alternative perspective a complement to the IPCC approach is needed to assess these issues and actions that are needed to avoid handing young people a dire situation that is out of their control. This alternative approach will make more use of ongoing observations to drive modeling and more use of paleoclimate to test modeling and test our understanding. As of today, the threats of AMOC shutdown and sea level rise are poorly understood, but better observations of polar ocean and ice changes in response to the present accelerated global warming have the potential to greatly improve our understanding.
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James Hansen et al: Global Warming Has Accelerated: Are the United Nations and the Public Well-Informed? (Original Post)
OKIsItJustMe
Tuesday
OP
James Hansen and Pushker Kharecha: Global Warming Acceleration and Recovery
OKIsItJustMe
Thursday
#1
OKIsItJustMe
(21,047 posts)1. James Hansen and Pushker Kharecha: Global Warming Acceleration and Recovery
(No URL yet.)
Global Warming Acceleration and Recovery
6 February 2025
James Hansen and Pushker Kharecha
Here we make available Global Warming Has Accelerated, including the Supplementary Material (SM), in one document and the webinar discussing the paper.
The SM shows that the rate of freshwater injection on the North Atlantic Ocean assumed in Ice Melt, Sea Level Rise, and Superstorms was realistic, averaged over the past two decades, but the rate of ice melt did not increase in the past decade. The present acceleration of global warming, which is especially great in the North Atlantic and North Pacific, makes it likely that the rate of ice melt will now accelerate, thus affecting the likelihood of shutdown of the Atlantic Meridional Overturning Circulation (AMOC) and, in turn, the threat of large sea level rise.
The SM, see below, also addresses reactions to our paper. One more comment may be helpful. Why do we say that global temperature will not go down much (i.e., the world is already at +1.5°C and 2025 will be warmer than the kibitzers expect) is only partly due to the ship aerosol forcing it is due more to high climate sensitivity. We evaluated the 1.7 W/m² darkening of Earth as about 0.5 W/m² ship aerosols, 0.15 W/m² sea ice albedo, but mostly cloud feedback. The cloud feedback operates in both hemispheres and is the main reason that global SST will not fall much and will soon be rising further. The ship aerosol forcing and cloud feedback work together in the North Pacific and North Atlantic, so warming is fastest there, but warming is a global phenomenon.
We have been cooperating with David Beerling and colleagues for years on one the many things that eventually may help restore a propitious climate: actions to accelerate weathering removal of atmospheric CO₂. A new paper on that is just published; we briefly discussed this once and will try to write more soon, but further information is available from the University of Sheffield.
6 February 2025
James Hansen and Pushker Kharecha
Here we make available Global Warming Has Accelerated, including the Supplementary Material (SM), in one document and the webinar discussing the paper.
The SM shows that the rate of freshwater injection on the North Atlantic Ocean assumed in Ice Melt, Sea Level Rise, and Superstorms was realistic, averaged over the past two decades, but the rate of ice melt did not increase in the past decade. The present acceleration of global warming, which is especially great in the North Atlantic and North Pacific, makes it likely that the rate of ice melt will now accelerate, thus affecting the likelihood of shutdown of the Atlantic Meridional Overturning Circulation (AMOC) and, in turn, the threat of large sea level rise.
The SM, see below, also addresses reactions to our paper. One more comment may be helpful. Why do we say that global temperature will not go down much (i.e., the world is already at +1.5°C and 2025 will be warmer than the kibitzers expect) is only partly due to the ship aerosol forcing it is due more to high climate sensitivity. We evaluated the 1.7 W/m² darkening of Earth as about 0.5 W/m² ship aerosols, 0.15 W/m² sea ice albedo, but mostly cloud feedback. The cloud feedback operates in both hemispheres and is the main reason that global SST will not fall much and will soon be rising further. The ship aerosol forcing and cloud feedback work together in the North Pacific and North Atlantic, so warming is fastest there, but warming is a global phenomenon.
We have been cooperating with David Beerling and colleagues for years on one the many things that eventually may help restore a propitious climate: actions to accelerate weathering removal of atmospheric CO₂. A new paper on that is just published; we briefly discussed this once and will try to write more soon, but further information is available from the University of Sheffield.