One challenge in climate research is determining exactly when the effects of human-caused climate change become distinguishable from natural climate variability. Detection of climate changes often indicates a need for adaptation. New research led by CIRES graduate student Jonah Shaw finds human-caused warming was detected over more than half of Earth’s land area by the year 2000 and more than 90 percent of the globe by 2020. 

Shaw and co-author Nathan Lenssen (Colorado School of Mines) combined data from hundreds of long-term observing sites with four climate models to ensure the accuracy of their results. They found that on regional scales (looking at areas roughly the size of Colorado), climate warming became statistically detectable during the late 20th century. There are large regional discrepancies due to uncertain and incomplete observations, however, and many of the regions most impacted by observational uncertainty lie in under-studied regions in the Global South. This work increases the confidence of key findings reported by the Intergovernmental Panel on Climate Change (IPCC).

“The reason we’re doing this regionally rather than globally is that regionally is where the impacts of climate change happen,” Shaw said.“Even when we’re as conservative as possible, we can detect these regional local changes just about everywhere over the land surface.” 

Read the paper in Environmental Research Letters.