How do we know what past megadroughts were like?
Trees grow annual tree rings every year.
How do tree rings help compare past megadroughts to drought today?
So we took advantage of this really high density of drought-sensitive tree ring records to reconstruct how soil moisture has varied over the last 1,200 years.
In 2012 I did a study using tree records across the Southwest.
And that’s what we’ve seen in western North America, where the last century … has not seen really big trends in precipitation.
And climate models say that all of that warming is due to human-caused climate change.
We can retroactively calculate how soil moisture would have been impacted if the long-term warming trends that were caused by humans had never occurred.
It would still have been bad; it would compete with the worst droughts of the last century.
But it wouldn’t be able to compete with the droughts of the last millennium [without climate change].