New method predicts 2 to 5 degrees more at the end of the century globally

2023-11-16 18:08:20

A new method for analyzing climate models brings together information from several lines of evidence to represent the Earth’s climate sensitivity. – JASON SMITH, OAK RIDGE NATIONAL LABORATORY

MADRID, 16 Nov. (EUROPA PRESS) –

A new method for statistically analyze climate models with greater fidelity estimates that global temperatures will rise between 2 and 5 degrees Celsius by the end of the century.

This projection, published in Nature Communications Earth & Environmentaligns with previous projections, although this novel framework is more inclusive and avoids model rejection, which was common practice in previous methods.

“We do not judge models individually“said Elias Massoud, a computational ecohydrologist at ORNL (Oak Ridge National Laboratory). “Instead, we look at how they can be combined, using their combined information to get projections of the future.”

A key parameter for these models, known as equilibrium climate sensitivity or ECS, describes the relationship between the change in carbon dioxide and the corresponding warming. Although the Earth system has a true ECS, it is not a measurable quantity. Different lines of evidence can provide a plausible picture of the Earth’s true ECS, which can alleviate the uncertainty of simulation models.

However, many models assume a high ECS and predict higher temperatures in response to more atmospheric carbon dioxide than occurs in the real Earth system. Since these models provide estimates about future conditions to scientists and policymakers, It is important to ensure that they represent conditions on Earth as closely as possible.

The above methods mitigated this problem by removing models with a high ECS value. “That was a heavy-handed approach,” Massoud said. “The models that were discarded could have good information that we need, especially to understand the extremes of things.”

“Instead, we adopted a tool called Bayesian Model Averaging, which is a way to combine models with variable influence when estimating their distribution,” Massoud said. “We used this to constrain the ECS in these models, which allowed us to project future conditions without the ‘hot model problem'”.

Many models come from similar code or have the same parameters, raising concerns about model independence. “If two models are dependent, they give the same information,” said Massoud it’s a statement. “Our work uses the results of the weights to estimate how much independence each shows and then factors it into their influenceso that the same information is not counted twice.”

This new method provides a framework for how to better understand a collection of climate models. The model weights included in this research informed the Fifth National Climate Assessment, a report released Nov. 14 that measures the impacts of climate change in the United States.

“Our work integrates model data with observed data to obtain the best estimate of the state of the Earth system“Massoud said. “This allows scientists to make more accurate and precise projections about how the Earth and climate are changing.”