Climate models

The high end of climate sensitivity in new climate models considered less plausible – ScienceDaily


A recent analysis of the latest generation of climate models – known as CMIP6 – provides a caveat on interpreting climate simulations as scientists develop more sensitive and sophisticated projections of how the Earth will react to levels. increasing amounts of carbon dioxide in the atmosphere.

Researchers at Princeton University and the University of Miami have reported that newer models with high “climate sensitivity” – meaning they predict much greater global warming from the same levels of dioxide of atmospheric carbon than other models – do not provide a plausible scenario of Earth’s future climate.

These models overestimate the global cooling effect that results from interactions between clouds and aerosols and project that clouds will moderate the warming induced by greenhouse gases – particularly in the northern hemisphere – much more than what the climate records show, the researchers reported in the journal. Geophysical research letters.

Instead, the researchers found that models with lower climate sensitivity are more consistent with the observed temperature differences between the northern and southern hemispheres and, therefore, are more accurate representations of projected climate change than the models. more recent. The study was supported by the Carbon Mitigation Initiative (CMI) based at the High Meadows Environmental Institute (HMEI) in Princeton.

These findings are potentially important for climate change policy, explained co-author Gabriel Vecchi, professor of geosciences at Princeton and the High Meadows Environmental Institute and senior researcher at CMI. Because models with higher climate sensitivity predict greater warming in greenhouse gas emissions, they also predict more serious – and imminent – consequences such as more extreme sea level rise and waves. heat.

Highly sensitive climate models predict an increase in the global average temperature of 2 to 6 degrees Celsius below current levels of carbon dioxide. The current scientific consensus is that the increase should be kept below 2 degrees to avoid catastrophic effects. The 2016 Paris Agreement sets the threshold at 1.5 degrees Celsius.

“Higher climate sensitivity would obviously require much more aggressive carbon mitigation,” Vecchi said. “Society would need to reduce carbon emissions much faster to meet the Paris Agreement targets and keep global warming below 2 degrees Celsius. Reducing the uncertainty of climate sensitivity helps us develop a more reliable and precise strategy for dealing with climate change.

The researchers found that the models of high and low climate sensitivity correspond to global temperatures observed during the 20th century. Models of higher sensitivity, however, include a stronger cooling effect of 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 careful about the outcome of a model, even if the models accurately represent past global warming,” said first author Chenggong Wang, Ph.D. candidate for Princeton’s program in atmospheric and oceanic sciences. “We show that the global average hides important details about the patterns of temperature change.”

In addition to the main findings, the study helps shed light on how clouds can moderate warming both in models and in the real world on a large and small scale.

“Clouds can amplify global warming and cause warming to accelerate rapidly over the next century,” said co-author Wenchang Yang, associate geoscience researcher at Princeton. “In short, improving our understanding and our ability to correctly simulate clouds is really the key to more reliable predictions of the future.”

Scientists at Princeton and other institutions have recently focused on the effect of clouds on climate change. Related research includes two papers by Amilcare Porporato, Professor Thomas J. Wu ’94 of Civil and Environmental Engineering from Princeton and the High Meadows Environmental Institute and a member of the CMI leadership team, which reported on the future effect of heat-induced clouds on solar energy. 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, professor of atmospheric sciences at the University of Miami. “It is encouraging that, as this study shows, there are still many treasures that we can exploit from historical climate observations that are helping to refine the interpretations we are getting of the global average temperature change. “

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Material provided by Princeton University. Original written by Morgan Kelly. Note: Content can be changed for style and length.