Warm nights more common in Maine as Summer nighttime temperatures rise significantly
PORTLAND (WGME) — As summer sets in, we expect hot days, but increasingly, the nights aren’t bringing the relief they once did.
Across the U.S., and here in Maine, summer nights are getting noticeably warmer, and climate change is playing a major role.
One tool that helps scientists measure this impact is the Climate Shift Index (CSI). This index estimates how much more likely a specific temperature has become due to human-driven climate change. For instance, a CSI of 2 means a particular temperature is now twice as likely to occur because of global warming.
While daytime temperatures are certainly rising, nighttime warming is happening even faster in many areas. In parts of the Southwest, some locations have experienced more than 60 summer nights per year that are at least twice as likely to happen due to climate change.
Here in Maine, the trend is clear. Summer nighttime temperatures have climbed significantly over the last few decades. Since 1970, average summer nights are now nearly 4F warmer. This has resulted in more than 30 nights per year with temperatures classified as above normal and at least twice as likely because of climate change.
To put this into perspective, consider what we might call an “uncomfortably warm night” in Maine, when temperatures don’t dip below 70F. In the 1970s, 1980s, and 1990s, Portland typically saw about 8 of these nights per decade. But the numbers have climbed rapidly:
- 15 nights in the 2000s
- 21 nights in the 2010s
- And in just the first half of the 2020s, we’ve already recorded 24 such nights.
This sharp increase in warm nights is more than just a statistical trend as it affects sleep quality, public health and even energy demand. With climate change continuing to drive warming, warm summer nights are becoming the new normal in Maine.