When it comes to climate change, scientists agree there are still many unknowns that can affect local weather patterns. One thing that’s universally agreed upon, however, is that the planet is heating up and will continue to do so until humans drawdown greenhouse gases in the atmosphere.
So when a team of IU researchers noticed that observational data collected from weather stations along the coast of California showed cooling trends over the late 20th century, they suspected something was wrong with the data. The ensuing investigation led to findings that can help inform future climate modeling efforts relevant to regions, states, and cities. The results of the study have been published in the journal Geophysical Research Letters.
Climate researchers and policymakers rely on climate models to predict temperature and weather trends and the anticipated impacts of climate change. Downscaled models are particularly useful, as they derive finer-scale projections from global models. Therefore, it is vital to determine which downscaled models are most accurate.
To investigate the apparent cooling in coastal California, IU postdoctoral research fellow Alexander Charn and his colleagues took 32 downscaled simulations of the California coast and compared them to six different observational datasets of temperature trends in the same area. They found that of the four datasets that showed cooling, all had failed to take into account artificial jumps in temperature caused by historical changes in the instruments, such as weather stations and satellites, recording the data. The two datasets that did account for these changes showed coastal warming trends.
Though this research focused on California, Charn said that the lesson can be applied anywhere.
“Observational records anywhere, not just in California, have to be careful when calculating trends,” he said. “They have to account for artificial jumps in station records, caused, for example, by changes in station location. Datasets that do not take into account how the data is collected can ultimately distort the analysis of downscaled climate models.”
Charn and his colleagues also investigated how best to ensure that downscaled models predicted trends accurately. While models can be tuned to match historical observations of weather, Charn said it usually isn’t that simple.
“You can have a model that does really well in the past, but that doesn’t mean it will perform well in the future,” he said.
One source of inaccuracy identified by the team is the past and future factors fueling climate change. Aerosols in the atmosphere were once a major driver of climate change; moving forward, researchers predict that greenhouse gases will be the more dominant force. Models that fail to account for this fact likely won’t continue to predict climate trends with the same level of accuracy.
For this reason, Charn said he plans to continue investigating the best way to use downscaled models. Charn and his colleagues are working on improving the method of determining which models are more accurate than others, and they plan to test out their approach on the newest set of simulations released by the climate modeling community. Further down the road, he hopes to develop a means of testing models’ predictive capabilities for the effects of aerosols and greenhouse gases separately.
Though he emphasized the importance of downscaled models in local decision making, Charn also recommended caution when it comes to interpreting model results, as so many variables, both known and unknown, can affect the climate.
“Be wary if someone hands you a very precise estimate of what’s going to happen in the future,” Charn said. “Even if the estimate is good, the precision is probably unfounded.”
About the Environmental Resilience Institute
Indiana University’s Environmental Resilience Institute brings together a broad coalition of government, business, nonprofit, and community leaders to help Indiana and the Midwest better prepare for the challenges of environmental change. By integrating research, education, and community, ERI is working to create a more sustainable, equitable, and prosperous future. Learn more at eri.iu.edu.