Many Scientists Are Skeptical of the Extreme Warming Predicted by Next-Generation Climate Models
Early runs of some next-generation climate models to be included in the next United Nations report predict way more warming than their predecessors.
While modelers are trying to understand exactly why this happened, many scientists are skeptical there’s enough estimates to justify the new warmed-up models.
“These new climate model runs are basically gifts to skeptics, since they clearly reduce the credibility of the climate models for attributions of recent warming and also for 21st century projections,” climate scientist Judith Curry told The Daily Caller News Foundation.
So far, at least eight of the 15 models have extremely high estimates of climate sensitivity. Climate sensitivity refers to the long-term warming from a doubling of carbon dioxide concentrations in the Earth’s atmosphere.
Climate sensitivity is a hotly debated topic, but nailing down a central estimate is crucial for U.N. Intergovernmental Panel on Climate Change assessments that try to forecast long-term climate warming.
A higher climate sensitivity measure will yield more alarming results, but not all scientists are convinced there’s enough evidence for high climate sensitivity estimates.
Curry said models with climate sensitivity above 4 degrees Celsius don’t do a good job of replicating past temperatures. For example, early runs of the U.S. Energy Department’s climate model, called E3SM, doesn’t capture the current warming trend very well.
The latest E3SM runs peg climate sensitivity at 5.3 degrees Celsius. That’s well outside the range of what the IPCC considers to be likely — which is somewhere between 1.5 and 4.5 degrees Celsius.
The U.K. Met Office’s two new models both put climate sensitivity well above 5 degrees Celsius. Part of the advances the Met Office says it’s made in the latest suite of climate models is to more detailed simulation of cloud coverage.
New models give a “more detailed representation of sea-ice,” “a more accurate representation of heat exchange between ocean and atmosphere,” and ocean and atmospheric temperature structure, the Met Office says.
“One cannot take such results seriously,” Cliff Mass, an atmospheric scientist at the University of Washington, told TheDCNF. “Sometimes when you add detail and complexity to models their predictions degrade; this is certainly the case with weather forecasting models.”
“It appears that these new parameterizations have introduced a bunch of positive feedbacks, while not including some negative feedbacks,” echoed Curry.
However, Mass noted that models predicting extreme warming were only a subset of what’s called the Coupled Model Intercomparison Project Phase 6 (CMIP6), which will be used in the next IPCC report due out in 2021.
“All the models don’t show such increased sensitivity to greenhouse gas increases,” Mass said.
More than 100 climate models from scientific institutions around the world have been registered for CMIP6, including the Energy Department and National Aeronautics and Space Administration.
Scientists have been working for decades to give a more accurate picture of climate sensitivity, but without much success. In fact, the likely range of the atmosphere’s response to a doubling of CO2 has increased in recent years.
The IPCC’s latest assessment, released in 2014, lowered the bottom range of climate sensitivity from 2 degrees to 1.5 degrees Celsius — a not to studies that show climate sensitivity may actually be pretty low.
Curry’s research has suggested that climate sensitivity is quite low, about 1.6 degrees Celsius. She’s skeptical of higher estimates of climate sensitivity that are often seized upon by activists and the media to make dire predictions of climate catastrophe.
“These new simulations with high climate sensitivity may result in climate models being put back into their rightful place as tools to try to understand how the climate system works,” Curry said.
However, climate scientists caution that climate models are still in the early stages of development and will be fine-tuned before the next IPCC report is released.
“It’s still early stages of model result analysis to say anything definitive,” Olivier Boucher, a scientist at France’s Laboratoire de Météorologie Dynamique, told TheDCNF.
Boucher says further investigation is needed to figure out why climate models seem to be generating higher climate sensitivity ranges. He also said transient climate response, not climate sensitivity, might be a more relevant measure.
Transient climate response is the immediate warming once atmospheric CO2 levels are doubled. Boucher says this might be a more useful measurement for warming predictions for this century.
“The fact that models have large [equilibrium climate sensitivity] is one line of evidence, which has to be balanced by other lines of evidence, of course,” Boucher said.
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