2021 was the hottest year in more than 1000 years

As I sit here writing this post, we are experiencing unseasonably hot (not warm) temperatures and are blanketed by smoke from an unprecedented fire season. As a result, this research by Heeter and colleagues (2023) is sadly not surprising. But it is still important to consider and pretty cool how it was done.

We don’t have temperature records for this long, but trees do. Trees, with their annual growth rings showing how much a tree grew each year, are records of historical temperatures. Typically, weather is determined by the width of a tree ring. Wetter years result in greater growth. But Heeter et al used a different approach that is more directly reflective of hot temperatures.

Plant cells have a cell wall around the outside. This wall is thicker when the weather is hotter. And that thickness shows up in how much blue light is reflected when a visible light source is shone on a tree core. The thicker cell walls reflect less blue light. This gives a means of determining the temperature when those cell walls were built.

The results match what has been reported through other studies. The hot temperatures on the western side of North America between 1979 and 2021 are hotter than any seen in more than 1000 years. The next closest was 1028-1096. But, it’s not even really close. 2021 saw an average temperature of 18.9°C, which is two degrees warmer than the warmest year in the medieval heat wave.

There’s not too much more to say at this point. We know that serious changes need to happen if we want to change the current direction. From personal to societal changes we need it all. What can you do to change the direction we’re heading?