A recent analysis of the latest generation of climate models – known as CMIP6 – provides a cautious history for interpreting climate simulations as scientists develop more sensitive and sophisticated predictions about how the Earth will respond to rising levels of carbon dioxide in the atmosphere.
Researchers at Princeton University and the University of Miami report that newer models with high “climate sensitivity” – meaning they predict much greater global warming from the same levels of atmospheric carbon dioxide as other models – do not provide plausible scenario for the future climate of the Earth.
These models overestimate the global cooling effect that results from cloud-aerosol interactions and predict that clouds will control greenhouse gas warming – especially in the northern hemisphere – far more than climate records show. reported in the magazine Geophysical research letters.
Instead, the researchers found that models with lower sensitivity to climate were more compatible with the observed temperature differences between the northern and southern hemispheres, and thus were more accurate images of projected climate change than newer models. The study is supported by the Carbon Reduction Initiative (CMI), based at the High Meadows Environmental Institute in Princeton (HMEI).
These findings are potentially significant in terms of climate change policy, explained co-author Gabriel Vecky, a professor of geology at Princeton and the High Meadows Institute for the Environment and principal investigator at CMI. As models with higher climate sensitivity predict greater warming from greenhouse gas emissions, they also project more dire and immediate consequences such as more extreme sea level rise and heat waves.
Models with high sensitivity to climate predict an increase in the average global temperature of 2 to 6 degrees Celsius at current carbon dioxide levels. The current scientific consensus is that the increase should be maintained below 2 degrees to avoid catastrophic effects. The 2016 Paris Agreement sets the threshold at 1.5 degrees Celsius.
“Higher climate sensitivity will obviously require much more aggressive carbon mitigation,” Veki said. “Society will need to reduce carbon emissions much faster to achieve the goals of the Paris Agreement and keep global warming below 2 degrees Celsius. Reducing uncertainty about climate sensitivity helps us make a more credible and accurate strategy for tackling climate change. “
Researchers have found that both high and low climate sensitivities correspond to global temperatures observed in the 20th century. However, the higher sensitivity models include a stronger cooling effect from the aerosol-cloud interaction, which compensates for the greater warming due to greenhouse gases. In addition, the models have aerosol emissions occurring mainly in the northern hemisphere, which is not consistent with the observations.
“Our results remind us that we need to be cautious about the results of the model, even if the models accurately represent past global warming,” said first author Chenggong Wang, MD. candidate in the Princeton program in atmospheric and ocean sciences. “We show that the global average hides important details about temperature change patterns.”
In addition to the main findings, the study helps shed light on how clouds can moderate warming in both large and small-scale models in the real world.
“Clouds could increase global warming and could accelerate global warming in the next century,” said co-author Wenchang Young, an associate geologist at Princeton. “In short, improving our understanding and ability to properly simulate clouds is really the key to more reliable forecasts for the future.”
Scientists from Princeton and other institutions have recently turned their attention to the effect that clouds have on climate change. Related research includes two papers by Amilcare Porporato, Professor of Civil and Environmental Engineering Thomas J. Wu ’94 of Princeton and the High Meadows Institute for the Environment, and a member of CMI’s management team that report on the future effect of heat-induced clouds. on solar power and how climate models underestimate the cooling effect of the daily cloud cycle.
“Understanding how clouds modulate climate change is at the forefront of climate research,” said co-author Brian Soden, a professor of atmospheric science at the University of Miami. “It is encouraging that, as this study shows, there are still many treasures we can use from historical climate observations that help improve the interpretations we get from global average temperature change.”
The report “Compensation between cloud feedback and aerosol-cloud interaction in CMIP6 models” was published in the February 28 issue of Geophysical research letters
Ice Age tests reveal challenges in the sensitivity of the climate model
Chenggong Wang et al, Compensation between cloud feedback and aerosol-cloud interaction in CMIP6 models, Geophysical research letters (2021). DOI: 10.1029 / 2020GL091024
Provided by Princeton University
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