NOAA reported today that whis winter turned out to be the 4th warmest on record in the contiguous United States. That’s not surprising given how much the world has warmed over the past few decades. In fact, all of the seven warmest years in over 100 years of climate data have occurred since 1992, and over the past three decades, a warmer-than-average winter has been twice as likely as a cool one. These data are consistent with how scientists say global warming affects the weather. The risk of warm winters is increasing over time, but that doesn’t mean that cold winters disappear, similar to the way that loaded dice change the probability of a particular roll but don’t eliminate other possibilities.
In recent years, climate skeptics have seized upon cold winters as evidence that the climate is not changing, but single data points cannot provide evidence for or against global warming. Similarly, this past winter was unusually warm, but on its own, it does not constitute compelling evidence for a changing climate. Instead, long-term trends are the only way to discern if the climate is changing. NOAA provides an updated graph that shows the average winter temperature for the contiguous United States. The graph shows an upward trend in winter temperatures, and notably, the trend is not greatly affected by recent colder years like 2011 or 2010, or recent warm years like 2012 or 2006.
The warming trend is not confined to winters. Trends over the past century have also pointed to warmer springs, summers and falls, indicating an increased probability of warmer-than-normal conditions year round. This increase in the frequency of warm seasons increases the risk of extreme weather events including extreme heat, extreme precipitation, drought and wildfires.
Residents across the country should prepare for more warm winters in the future, which can mean less natural water storage because of reduced snowpacks in the west and the northward migration of pests across the country. However, the increased risk of a warm winter does not mean that cold weather will disappear. As recent winters have shown, unusually cold weather can still make an appearance, even resulting in colder than normal winters, during this abnormally warm decade. Preparing for increasingly extreme weather is an important part of resilience and adaptation to a shifting and more unpredictable climate.
Dan Huber is Science & Policy Fellow at C2ES.