Thomas Fire (IMAGE) University of Colorado at Boulder Caption The Thomas fire burned >113,000 hectares from early December 2017 to late January 2018, making it the largest fire in California's modern history. While large fires such as the Thomas fire gain much media attention, proportionally large fires in less fire-prone ecoregions can also be ecologically and economically costly. Nagy et al. defined large fires by ecoregion across the United States (U.S.) using government records of wildfires from 1992-2015 (~175,000 large fires). Of these large fires, humans started 92% and 65% of fires in the eastern and western U.S., respectively. Large human-caused fires occurred in wetter and windier locations and months on average than large lightning-caused fires and included >80,000 large fires in seasons when lightning-ignited fires were rare (i.e., spring, fall, and winter.) Credit NASA Earth Observatory Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.