Comparing model simulations of recent Earth warming with real-world observations may reveal differences resulting from a variety of factors, including model errors in the simulated response to increasing greenhouse gases and natural fluctuations in the climate system.
Natural climate variability, also called internal variability, can change regional and global atmospheric temperatures by moving heat within the climate system. Diagnosing the role of natural climate variability in recent decades is extremely important for both model validation and predictions of future warming.
To quantify the role of natural fluctuations in model observation differences, Livermore National Laboratory scientist Stephen Poe-Cheadley and colleagues discovered unique patterns of temperature trends associated with natural climate variability over the period 1980-2022. The research was published in the journal Geophysics Research Letters.
“The relative role of different drivers of model-observation differences in the warming pattern has important implications for our understanding of climate sensitivity and regional climate change,” said Poe-Cheadley, co-author of the study. “This study shows that natural changes in Earth’s climate likely contribute to significant differences in simulated and observed surface air temperature patterns.”
Previous studies by this research group have shown that natural climate variability reduces global warming and increases warming in the Arctic. The team analyzed multi-year trend patterns from hundreds of CMIP6 simulations (Phase Six of the Coupled Model Intercomparison Project, a global collaboration of climate modelers) in which natural variability warms the Arctic but has a global cooling effect. They found that most of these model simulations resulted in increased warming in the Barents Sea (off Norway) and the Kara Sea (north of Siberia) and cooling in the tropical eastern Pacific and Southern Ocean due to natural variability.
“Since these are the exact features reflected in the observed changes in surface temperature between 1980 and 2022, our study suggests that natural variability is an important component of many significant differences between models and observations,” said graduate student and lead author Aodhán Sweeney. A study conducted at the University of Washington (UW).
“The reason for the observed cooling in the tropical eastern Pacific and Southern Ocean over the past few decades is a hot topic in climatology. This study provides compelling evidence that natural variability may be largely responsible for the observed cooling in these regions,” said Qiang Fu, a UW professor and co-author of the paper.
The team found that a rare configuration of natural climate variability (<3%) contributes to increased warming in the Arctic and simultaneous cooling of the tropical eastern Pacific and Southern Oceans, exactly mimicking the features reflected in observational records. Although this pattern of temperature change is not observed in the average simulations of CMIP6 models, each of the climate models considered in the study rarely (0.4-2.8%) produces a pattern similar to observations.
“By linking model biases in surface heating patterns to natural climate variability, our study restores confidence in the ability of climate models to produce realistic predictions of future climate change,” said co-author and Pacific Northwest National Research Fellow Hailong Wang. Laboratory (PNNL).
Although further research is needed to fully determine the causes of modeled and observed differences in the global surface air temperature change model, the team concluded that the identified internal variability pattern and its similarity to features reflected in observational records indicate that natural climate variability did indeed reduce global warming and reduce Arctic warming over the period 1980-2022. increased.
Source: Port Altele
