Disentangling regional climate change: assessing the contribution of global- and regional-scale anthropogenic factors to observed regional warming

Abstract

While the influence of uniformly-distributed well-mixed greenhouse gas emissions on global warming is well-documented and robustly attributed through multiple lines of evidence, regional attribution remains more challenging and dependent on the performance and resolution of climate models. This study investigates the extent to which observed regional temperature trends are attributable to global-scale anthropogenic factors, mainly the direct effects of CO2, aiming to differentiate the portion of the change attributable to regional-scale drivers and local feedback mechanisms. To quantify the contribution of global– and regional–scale climate drivers to observed temperature change, we conducted regression analyses using the observed temperature change in HadCRUT4 and the Global Warming Index (GWI) derived from global radiative forcing series. Results indicate that in certain regions — specifically West Asia, East N. America, and West Africa — 62±4%, 61±12%, and 58±3% of the warming observed over 1991-2020 can be attributed to global anthropogenic warming, primarily the direct effects of CO2. The remaining portion, which represents 22±5%, 21±13%, and 27±3% of the observed warming, is attributable to regional drivers. The Mediterranean showcases high sensitivity, with regional drivers contributing 31±8% of the observed 1.2°C warming, amplifying the warming attributed to global anthropogenic drivers, estimated at 55±7% of the warming. The Arctic Ocean along with the Russian-Arctic region exhibits a substantial contribution from regional drivers and local feedback mechanisms to the observed warming amplification, quantified at 43±10% of the 3°C warming over 1991-2020. Regional cooling drivers, however, are significant in East Asia and the Tibetan Plateau, with the latter experiencing a cooling contribution of -42±11%. By breaking down the contributions of climate drivers into global and regional-scale components, we gain valuable insights into the local climate mechanisms responsible for the observed regional warming, which is a crucial factor that affects agriculture, ecosystems and societies.