NOAA’s extreme weather expert, Martin Hoerling, slammed Hansen on Andy Revkin’s blog yesterday.
“Over the next several decades, the Western United States and the semi-arid region from North Dakota to Texas will develop semi-permanent drought, with rain, when it does come, occurring in extreme events with heavy flooding. Economic losses would be incalculable. More and more of the Midwest would be a dust bowl. California’s Central Valley could no longer be irrigated. Food prices would rise to unprecedented levels.”
He doesnt define “several decades,” but a reasonable assumption is that he refers to a period from today through mid-century. I am unaware of any projection for “semi-permanent” drought in this time frame over the expansive region of the Central Great Plains. He implies the drought will be due to a lack of rain (except for the brief, and ineffective downpours). I am unaware of indications, from model projections, for a material decline in mean rainfall. Indeed, that region has seen a general increase in rainfall over the long term during most seasons (certainly no material decline). Also, for the warm season when evaporative loss is especially effective, the climate of the central Great Plains has not become materially warmer (perhaps even cooled) since 1900. In other words, climate conditions in the growing season of the Central Great Plains are today not materially different from those existing 100 years ago. This observational fact belies the expectations from climate simulations and, in truth, our science lacks a good explanation for this discrepancy.
The Hansen piece is policy more than it is science, to be sure, and one can read it for the former. But facts should, and do, matter to some. The vision of a Midwest Dustbowl is a scary one, and the author appears intent to instill fear rather than reason.
The article makes these additional assertions:
“The global warming signal is now louder than the noise of random weather…”
This is patently false. Take temperature over the U.S. as an example. The variability of daily temperature over the U.S. is much larger than the anthropogenic warming signal at the time scales of local weather. Depending on season and location, the disparity is at least a factor of 5 to 10.
I think that a more scientifically justifiable statement, at least for the U.S. and extratropical land areas is that daily weather noise continues to drum out the siren call of climate change on local, weather scales.
Hansen goes on to assert that:
“Extremely hot summers have increased noticeably. We can say with high confidence that the recent heat waves in Texas and Russia, and the one in Europe in 2003, which killed tens of thousands, were not natural events — they were caused by human-induced climate change.”
Published scientific studies on the Russian heat wave indicate this claim to be false. Our own study on the Texas heat wave and drought, submitted this week to the Journal of Climate, likewise shows that that event was not caused by human-induced climate change. These are not de novoevents, but upon scientific scrutiny, one finds both the Russian and Texas extreme events to be part of the physics of what has driven variability in those regions over the past century. This is not to say that climate change didn’t contribute to those cases, but their intensity owes to natural, not human, causes.
The closing comment by Hansen is then all the more ironic, though not surprising knowing he often writes from passion and not reason:
“The science of the situation is clear — it’s time for the politics to follow. ”
Let me borrow from a recent excellent piece in New Scientist by tornado expert Dr. Harold Brooks regarding the global warming and tornado debate, and state:
“Those who continue to talk in certain terms of how local weather extremes are the result of human climate change are failing to heed all the available evidence.”