Climate change is increasingly costly in the U.S. And its manmade nature is increasingly clear.

Residents of California, Puerto Rico, and Texas will need no reminder that the climate was unusually cruel in 2017. But now official statistics are putting those fires and storms in perspective. The United States was struck by 16 climate and weather disasters that each caused at least a billion dollars in damage. At that clip, 2017 now matches 2011 as having the greatest number of billion-dollar disasters.

But 2017 blew through the previous record for the cumulative cost of these events. Losses in 2017 exceeded $306.2 billion, well above the $214.8 billion in losses during 2005 (values are adjusted for inflation). For more background on the connection between climate change and extreme weather, explore C2ES resources on extreme weather.

Recent cold weather in parts of the U.S. might leave some people wondering whether the 2017 events were a fluke, as opposed to indicators of long-term trends. But the body of evidence supports a long-term warming trend, and no single event disproves that.

Since the beginning of the 20^th century, cold waves – such as the one experienced by much of the U.S. last week – have actually become less frequent while heat waves have become more frequent. Also, the coldest day of each year is warmer than it used to be (the hottest day of the year is warmer too).

Moreover, there is suggestive evidence linking the warming Arctic with the sorts of winter weather patterns that bring prolonged cold spells to parts of North America. A causal mechanism has yet to be definitively identified, though many studies are underway.

Of course, not every individual weather event or phenomenon carries the mark of climate change. Scientists can investigate this question in a statistically rigorous method known as event attribution. Since 2012, an annual special report in the Bulletin of the American Meteorological Society (BAMS) has published a collection of attribution studies of extreme weather events of the preceding year. Importantly, when the report’s editors are reviewing proposed articles for inclusion, they are not provided the findings of whether the articles determined a climate change link. This blind review process helps reduce bias in the collected findings.

In the most recent BAMS special report, released December 17, climate change was found to be a “significant driver” in 21 of 27 weather events studied, or in other words climate change made those events more likely. Importantly, three events were determined to be entirely outside the range of natural variability, meaning these events would not have occurred at all if man-made greenhouse gases were not causing the climate to change.

The unmistakable conclusion is that human-induced warming is inflicting an increasing toll.  Despite the lack of leadership from Washington, efforts by states, cities and companies are thankfully continuing to reduce U.S. emissions.  But to have any hope that 2017 retains its dubious record, we must continue ramping up those efforts and working toward comprehensive solutions that greatly accelerate the low-carbon transition.