Climate FAQs: Regional Temperatures

Are regional temperature changes due to human activities?

Global average temperature increases in recent decades are primarily due to increasing greenhouse gas concentrations in the atmosphere resulting from human activities, such as the burning of fossil fuels. Yet, the magnitude of the anthropogenic influence on regional climate remains uncertain. A principal reason is because the effects of human activities are superimposed on the background "noise" of natural climate variability, which can be very large regionally.

Global warming does not mean that temperature increases are spatially uniform or monotonic: some places warm more than the average and some places cool. Regional changes in temperature are often associated with changes natural patterns (or modes) of the atmospheric and oceanic circulation, such as the El Niño/Southern Oscillation (ENSO) phenomenon. Changes in the climate system from human activities may affect these modes, however, so quantifying the anthropogenic and natural components of the observed warming on regional scales remains a difficult and critical research question.

Many global climate models, for instance, project changes in the statistics of ENSO variability with global warming, specifically of greater ENSO activity marked by larger interannual variations relative to the warmer mean state. More El Niño events would increase the probability of weather regimes that favor, for instance, regional cooling over the North Pacific Ocean with warming over much of northwest North America. Yet, the details of ENSO are not well enough simulated in climate models to have full confidence in these projected changes, in part because the positive atmosphere-ocean feedbacks involved with ENSO mean that small errors in simulating the relevant processes can be amplified.

Thus, while it is likely that changes in ENSO and other natural modes of climate variability will occur as a result of anthropogenic climate change, their nature, how large and rapid they will be, and their implications for regional climate change around the world remain uncertain.