Satellite observations and computer simulations can be used to understand past and future climate changes.
Satellite observations show less warming than climate model simulations in the tropics. Concerns have been raised about models overstating future temperature changes.
The model-satellite difference can be explained by natural fluctuations in Earth's climate and imperfections in climate-model forcing agents.
Stephen Po-Chedley said that natural climate variability appears to have masked warming over the satellite era.
An improved understanding of the causes of historical changes in climate and increased confidence in model simulations of continued global warming have been provided by the results of the study.
Although the Earth is warming as a result of human emissions of carbon dioxide, natural variations in the Earth's climate can temporarily accelerate or diminish this overall warming trend. Natural fluctuations in climate such as the Interdecadal Pacific Oscillation can be used to regulate the rate of warming.
The influence of natural variability on warming was quantified by these surface temperature patterns. Thousands of maps from climate model simulations were considered by the research team. The team trained machines to relate the pattern of surface warming to the overall magnitude of warming. The machine-learning approach was able to untangle the component of atmospheric warming due to natural climate oscillations versus warming from other causes.
Natural oscillations reduced the real-world tropical tropospheric warming trend by 25% over the satellite era when this approach was applied. Climate models only match the observations by chance, and the timing and sequence of the fluctuations are different in each simulation. Climate model simulations tend to be more accurate than satellite observations of tropical tropospheric temperature because of partial warming by natural variability.
Model forcing agents can affect comparisons between observations and models. Climate is influenced by external factors, such as historical changes in solar intensity, volcanic eruptions, greenhouse gas concentrations, and aerosol emissions. Climate model simulations use information on these factors. Model simulations can be affected by imperfect inputs.
Recent research published in Geophysical Research Letters and led by John Fasullo, a scientist at the National Center for Atmospheric Research and co-author, shows that biases in aerosol emissions can artificially enhance surface warming beginning in the mid 1990s.
The new study looked at whether biases in the burning of aerosols affect warming in the tropics.
The discontinuities in the burning aerosol emissions used in model simulations affect the temperature in the tropics. This result is specific to NCAR's Community Earth System Model, but it is likely that other climate models are affected as well.
The findings reduced satellite warming from natural climate variability and overestimation of model warming due to a problem in the aerosol forcing.
There are differences in the rate of tropical tropospheric warming. 10.1073/pnas.
The Spurious Late HistoricalEra Warming inCESM2 was written by J. T. Fasullo and his team. Stephen Po-Chedley and his co-authors wrote a paper titled "1029/2021GL097420."
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