NOAA scientist: natural phenomenon principal cause; no link found to global warming
As a followup to my earlier post on the possible connection between global warming and the Russian heat wave, I’ve been trying to catch up with Martin Hoerling. Marty is a research meteorologist, specializing in climate dynamics, in NOAA’s Earth System Research Laboratory located here in Boulder, Colorado.
Today, we finally connected. My interview with Hoerling will air on KGNU FM’s “How on Earth” science show at a later date. But for now, I thought I would share some of the essential highlights.
First, though, I must give credit where credit is due: This morning, Andrew Revkin wrote about a report from the Climate Science Investigation team, or CSI, a group at NOAA that Hoerling heads. As Revkin reported today, back on August 13 CSI published a draft report online concluding that a natural phenomenon called “atmospheric blocking” was the principal cause of the extreme heat in western Russia. The CSI group found no evidence that the long-lasting and astonishingly intense heat wave was caused by global warming.
[UPDATE 8/25 11:30 a.m.: Kevin Trenberth of the National Center for Atmospheric Research emailed me today to say that he disagreed with Hoerling on this issue. I will try to interview him soon. In the meantime, check out this document from a recent workshop on attribution of climate events.]
In my interview with Hoerling today, I asked him to elaborate on that conclusion.
When we say ‘principally’ we’re certainly not saying that [the blocking phenomenon] was the only cause. And rarely in climate and weather is there a single silver bullet that says this is caused by that . . . So principally what we’re saying when we use that word is that this event, the block, explains the majority of the temperature conditions that developed at the surface, but it may not explain all of it . . . So this would be your 800 pound gorilla, but there are still some other weights to be thrown around.
What is this blocking phenomenon?
“It puts the kabosh on the normal west to east movement of storms,” Hoerling said. In summer, those storms typically bring cool air to western Russian. With an atmospheric block, the storms become less frequent. “So the air becomes stagnant. If you’re underneath the block, it progressively becomes drier and warmer.”
Typically, a block like this last 10 days or so. But this one lasted much longer — basically from early July until middle of August. “It was very unusual for its persistence,” Hoerling said. “On top of it, it was strong, so it was very effective in shunting storms away.”
The CSI group reached its conclusions about the principal role of the block in causing the Russian heat wave by examining weather data going back 100 years. With this data they were able to establish a relationship between the intensity of blocks and temperature. And with that relationship in turn, they could ask a simple question: Given the observed intensity of the block that formed over Russia, what temperature does the relationship predict?It turns out that this number concurs quite closely to what actually happened.
In other words, what Hoerling and his CSI colleagues found is that the relationship actually predicted almost all of the heating that occurred. And that means no other possible cause was needed to explain most of what actually happened in Russia.
“The blocking explains a significant fraction of the temperature conditions that occurred consistent with the historical relationship of blocks and warm temperatures over this region,” Hoerling concluded.
But could global warming have made such an event more likely or more intense? Here was Hoerling’s answer:
The short answer is we actual don’t know whether blocks are expected to increase in their frequency in concert with the increasing burden of CO2. But what we do have are time series of blocking for the last 100 years. And constructing those times series like we have done reveals no evident trend in the frequency or intensity of blocks.
In other words, the 2010 situation isn’t following on the heels of a progression of more and more of these things happening ether over Russia, or frankly over any other place that we can see over the Northern Hemisphere. So it stands out as a . . . black swan. It comes out of the blue in terms of its severity. It does not follow on the heels of a progressive increased frequency.
And here’s another fascinating finding:
It’s interesting that there really isn’t a very strong warming over time in this region back to 1880. In other words, temperatures were warmer during the 1930s than they were in the early 2000’s. This year, however, is by all measures the warmest year . . . measured, since at least 1880.
It was, as Hoerling put it again, “like a black swan event. It was just off the scale.”
So if blocking events haven’t been progressively getting more frequent and more intense, and if there has been no trend of increasing warmth overall in this particular corner of the world, how can you blame the Russian heat wave on global warming?
The CSI team’s answer: You can’t.
Such an extreme event cannot be reconciled with a greenhouse gas forcing in any obvious way at this point in time. That’s not to say that research isn’t going to work at this and sort out the details; it has to be done that way . . . But at this point in time from what the data are telling us, and from what we know, it’s an event. It’s not a progression. It’s not linked to a trend. It’s not something that’s likely to happen again and again next year and a second year after that and a third year after that.
This was, Hoerling said, a “one in a 100 plus year event at least.”
That said, there is still a connection that can be made to global warming, according to Hoerling.
The situation we are experiencing fits a mold of what climate change is anticipated to do. And that’s very useful, because the change in climate that’s anticipated toward the end of the century will resemble in some very uncomfortable ways the extreme conditions that was experienced in 2010.
. . . if we’re struggling with these rare events, largely still from natural variability — if we’re struggling with how we adapt as a society to these situations, imagine our duress when the average summer day will look like the heat wave we just had, year in and year out. And that is the projection.
It’s still powerful to know that, wow, this is what climate change might feel like in about 70 years or so. And you know what? It’s not very pleasant.