A Washington Post analysis of more than a century of temperature data has found that much of the Northeast is in the grip of extreme warming, with winter heating up more quickly than other seasons.

The analysis, based on data from the National Oceanic and Atmospheric Administration, examines annual temperature data for the Lower 48 U.S. states and 3,107 individual counties, dating back to 1895.

The Post calculated the trend in yearly average temperature for each location over the entire 124-year period. We also comprehensively mapped the country to illustrate the varying levels of warming.

Here’s what we found:

1. Warming is very uneven. At the extreme, some regions show more than 2 degrees Celsius, or 3.6 degrees Fahrenheit, of warming. Others have barely warmed at all, or cooled slightly, over the entire period from 1895 to 2018. The average warming of the Lower 48 states, about 1 degree Celsius, obscures the severity of some of the nation’s temperature spikes.

2. Large regions show clear and strong warming signals. Scientists tell us that it is difficult to draw conclusions about temperature changes — and their causes — over small areas because of random variability and other complexities. But as The Post’s map makes clear, some large swaths of the country have seen consistent, remarkable warming. They include the Northeast, much of the U.S. border with Canada, and major parts of Utah, Colorado and Wyoming.

It’s important to note that this map merely tells us how much an individual place has changed over 124 years. It does not explain the cause. It is likely that factors other than global climate change, such as urbanization and regional air pollution, have also played a role. However, in recent years, as the pace of warming has picked up across the globe — including across the United States — the influence of human-fueled climate change has emerged as the key driver.

3. When it comes to the Northeast, the winter season has been transformed. When we examined the data more closely, it became clear that winter is the fastest-warming season in the Northeast, consistent with the expectations of climate scientists. We also found that the pace of warming over the past 60 years or so has accelerated. Once again, the Northeast led the pack, but on a state-by-state level, the Southwest also emerged with very fast warming rates in more recent decades.

4. Some of the fastest-warming regions have very few people living in them. Others, though, are highly populated. We found only a very weak relationship overall between the rate of warming in individual counties and their levels of population density. This suggests that urbanization, which is known to cause warming in local areas, cannot explain most features of this map. NOAA also tries to control for urbanization in its data set, though it cannot be ruled out as a cause.

In particular, because New York and Los Angeles are each part of larger warming regions, urban trends probably cannot fully explain their warming, although they might contribute, several experts told The Post.

Because these two highly populous regions have warmed quickly, The Post calculated that more than 30 million people live in counties that have warmed by 2 degrees Celsius or more since 1895.

5. These changes are already having major impacts, which vary depending on the location. In the Northeast, changes are being felt in agriculture — which is witnessing a strong shift of the seasons and of winter most of all — and in greater pressure from insects, such as ticks and agricultural pests, which plague humans and wildlife alike.

And that barely scratches the surface. What the data shows most of all is a portrait of very large — but uneven — change.

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