Effects of climate warming on natural and human systems are becoming increasingly visible across the globe. For example, the shattering of past yearly records for global high temperatures seems to be a near-annual event, with the five hottest years since 1880 all occurring since 2005 (1). Not coincidentally, the single hottest year on record, 2015, also broke records for area burned by wildfire in the United States (Fig. 1 A and B), eclipsing the previous high mark set just one decade prior (2). Scientists have known for some time that climate is a key driver of forest fires; records from the past and present (3⇓–5) provide strong evidence that warmer temperatures are associated with spikes in fire activity. Therefore, recent increases in wildfire activity as the planet warms are not a surprise. However, just how much of the recent increases in forest fire activity can be attributed to human-caused climate change vs. natural variability in climate? This question has profound scientific, management, and policy implications, yet answers have thus far remained elusive. In PNAS, Abatzoglou and Williams (6) present strong evidence that human-caused climate change is increasing wildfire activity across wide swaths of forested land in the western United States. They demonstrate that human-caused climate change has lengthened the annual fire season (i.e., the window of time each year with weather that is conducive to forest fires) and, since 1984, has doubled the cumulative area in the western United States that would have otherwise burned due to natural climate forcing alone.