Study Maps How Human-Caused Warming Shows Up Differently Across Regions

There is no question that the current rise in global temperature is caused by human activity, but how that warming shows up in different regions has remained harder to pin down, and observations do not always match climate model predictions. The southeastern Pacific and parts of the Southern Ocean have cooled, for example, and the subpolar North Atlantic has not warmed as much as expected. Researchers at the Max Planck Institute for Meteorology (MPI-M) have now developed an empirical tool to test how reliable the models' regional warming patterns really are.

The team, led by Aruhasi along with Dirk Olonscheck, Jochem Marotzke and Chao Li, used global surface temperature datasets from 1850 to 2022 to link regional observed temperatures with the globally averaged temperature rise, a value on which models and observations agree closely, in a study published in Science Advances. Comparing this "observed fingerprint" with the pattern predicted by climate models let the researchers pinpoint where model uncertainty is highest: the southeastern Pacific, the Southern Ocean, the subpolar North Atlantic, and the Arctic, a region famous for warming rapidly since the mid-20th century, with a temporary slowdown from the late 1990s to the early 2010s.

The study found that slowdown was due to natural variability, though a human influence was still evident, and the same held for the southeastern Pacific. In parts of the Southern Ocean and the subpolar North Atlantic, however, human-induced warming has not yet clearly emerged from the background noise of natural climate fluctuations. "The time it takes for the human signal to emerge from the noise varies by region," said lead author Aruhasi. "This 'emergence timescale' is often underestimated by models."

The method builds on the "detection and attribution" approach developed by Nobel laureate Klaus Hasselmann, founding director of MPI-M, and used by the Intergovernmental Panel on Climate Change. "The current period of satellite observations, at around 45 years, is sufficient to provide purely empirical evidence of human-induced warming in most regions," said MPI-M group leader and co-author Chao Li.