Our tour through last summer’s United States Department of Energy “red team” report on climate science brings us this week to Chapter 6.4 on extreme precipitation. It’s one of those topics we’ve discussed many times here at CDN so it comes as no surprise to us to learn that claims about increasing extreme rainfall in the US rely on cherry-picking just the right interval to examine, whereas the long term records show a distinct lack of trends. The section begins with a remarkable example of how short samples can create not only a misleading picture of how the climate has apparently changed, but can also lead disaster planners to underestimate what nature is capable of unleashing all on its own.
In a box on page 60 the report presents a table of extreme precipitation events (3-day, 5-day, 14-day and 30-day totals) for San Francisco back to 1895. The heaviest rainfall events all happened in 2023 except for the 30-day total which was in 1998. So recent years are wetter, climate change, your fault, etc. etc.
Since the IPCC and the US National Climate Assessment discuss US rainfall records only back to the 1950s this already draws on a much longer sample. But the DoE team don’t stop there and nor does the story.
The “red team” got San Francisco rainfall records back nearly another half-century, to 1850. And suddenly the picture changes dramatically. Now the heaviest rainfall events were all in the 1860s, especially 1862. 2023 isn’t even in 2nd place now, it falls to 3rd or 4th place. And the heavy rainfall events in the 1860s weren’t just worse than 2023, they were far worse. In fact the so-called ARkStorm of December 1861 through January 1862 dumped nearly 10 feet of water on parts of California and turned the entire Central Valley into a lake.
It gets worse. Going even further back, paleoclimate evidence has shown that the 1862 event was mild compared to flooding storms that have happened about every 300 years for the past 1,800 years and make 2023 look like a mere shower.
So, going back to the IPCC and NCA, when they look at changes since the 1950s and confidently declare we are seeing unprecedented increases in rainfall it must be climate change Gotcha!, we should ask them to show us what the data looked like over the previous 200 years or more. And if they reply that haven’t bothered to dig it up, then they’re not in a position to draw conclusions. Or not desirous of drawing valid ones.
The DoE team then widen their lens beyond California, and report on long-term rainfall records, a term here meaning from the late 1800s to 2024, from regions around the US. Only in the Northeast do they find evidence of an increasing trend, but it is linked to a cluster of years (1995-2014) during which hurricanes and tropical cyclones in the Atlantic drifted north before making landfall, which you can only blame on “climate change” if you blame everything on climate change.
In which case you’ll still be stumped by the fact that since 2014 the amounts of rain in the Northeast have returned to historical norms. The “red team” did look at research on whether that change might be attributable to greenhouse gases and found that it probably wasn’t. But it’s the usual Rorschach inkblot where people determined to see something will see it.
The DoE Report authors conclude:
“In summary, some U.S. regions show short-duration increases in extreme precipitation events, consistent with natural variability. But analysis of long term, nationwide historical records that considers the autocorrelation properties of precipitation data does not support the claim that extreme short-duration rainfall events are becoming more frequent or intense.”
Next week: tornadoes and flooding.
