It’s one thing to say the Northern Hemisphere summer of 2023 was the hottest of the 150 years people have been making measurements. This well-documented claim is often dismissed by skeptics of global warming who point out that the Earth has a long history of temperature fluctuations. That’s why it’s important that a new paper shows last summer was actually the hottest in the last 2,000 years — and that our current temperatures are even more of an outlier than we realized.
If all we had were the few decades of temperature readings to understand the past climate, we wouldn’t know whether our current warming was a major shift or a run-of-the-mill blip. Tree rings hold records that can go back thousands of years, giving us the perspective we need to understand what’s happening today.
In a paper published in Nature this week, scientists used tree rings not only to show long-term trends, but to plot Northern Hemisphere summer temperatures year by year for the last two millennia. 2023 was the hottest of them all. The next hottest 25 have all occurred since 1996. The next runner-up was way back in 246 CE.
The world’s understanding of global warming changed dramatically when scientists started to document long-term temperature trends using tree rings, ice cores, sediment layers and other natural temperature monitors. In 1998, scientists published the famous “hockey stick graph” covering the last 600 years. It showed that global temperatures rose and fell like gently rolling hills until the mid-20th century, when they suddenly soared.