What ever happened to rudimentary fact‐checking? There certainly wasn’t very much of it in a recent Associated Press screed conflating this summer’s weather and global warming.
True, AP’s Seth Borenstein had the good sense to never directly say that any particular event could be linked to global temperature. But his intent was obvious:
Climate scientists suggest that if you want a glimpse of some of the worst of global warming, take a look at U.S. weather in recent weeks.
Horrendous wildfires. Oppressive heat waves. Devastating droughts. Flooding from giant deluges. And a powerful freak wind storm called a derecho.
Before we go into the facts he didn’t check, let’s start with the obvious. If this summer’s weather is a result of global warming, then it had better be globally warm.
Below is a plot of the four major global temperature histories. This chart begins in 1979 because that is the starting date of the satellite history, which is likely to be the best record. The top three charts are from ground‐based thermometers, and the bottom is the satellite. (Don’t worry about the absolute difference between the records—they are referenced to different mean values.)
Global average temperature anomalies, 1979 through 2012 (red, NASA dataset; green, US Department of Commerce dataset; orange, University of East Anglia; blue, satellite records from University of Alabama‐Huntsville). The open circles are annual departures from average for each dataset. The last point (filled circle) is for the first five months of 2012.
All of these records share a common characteristic. They don’t show much warming since the late 1990s. More germane to Borenstein’s article is that, so far, 2012 is actually cool compared to the run of years since then. Such an inconvenient fact.
Now to the specifics. Borenstein reiterated the old rural legend about wildfires being enhanced by a bug called the western pine beetle. It works like this: bark beetles, which kill pine trees, survive in larger numbers during warm winters. Therefore warm winters result in more dead trees which results in more fuel which results in bigger fires. Logical, right?
Having done a bunch of research on pine beetles myself, I, too, once believed this. But it’s wrong. Last year, Martin Simard of the University of Wisconsinactually checked the facts, measured the amount of fuel left behind, and found that beetle‐infested forests have less fuel and that they suppress forest fires. The results were published in Ecological Monographs, about as prestigious a journal as there is in the field of Ecology.
Given the fact that 2012 is nothing special globally, then, under Borenstein’s logic, any odd weather from 1996 through now—when temperatures have been pretty constant—is consistent with global warming. That would include:
• Last year’s mild winter,
• The record length of time that the U.S. has seen since its last major hurricane strike, and
• The very low hurricane activity observed worldwide since 2005,
• The gigantic snowstorms that hit Washington DC in 2009-10,
• The very active hurricane season of 2005, and
• The lack of any trend whatsoever in severe tornadoes or economically‐adjusted weather damages.
But the largest insult in Borenstein’s article was his completely careless conflation of global warming with last week’s “derecho” that blew down trees in and around our Nation’s Capital, These systems, known more accurately as Mesoscale Convective Systems (MCS), are not rare. Some places average one a year. They tend to form in the daytime and usually (but not always) wane at night. Very few form east of the Appalachians, so they have to migrate over mountains that are very hostile to them to get to DC, which is why there is about one every four years here.
Whatever bad weather lands in Washington hits the media right between its eyes. Even modest snowstorms acquire cosmic importance and the local culture does its best to make things worse.
Politically and arboreally, Washington is a jungle. The modern cult of tree‐worship is especially popular. People squawk when the power company comes by to trim branches, so the power company goes away. When an ice storm, a decaying hurricane, or—yes—an MCS shows up, so goes the power. For millions, and sometimes for weeks.
With regard to global warming, some aspects of it would enhance derechos, and others would detract from them. It’s probably a push. Indeed, given the total lack of anything special about global temperatures in 2012, if derechos were being plumped by warming, then they would have become much more frequent over the last 16 years. Of course, there’s absolutely no evidence of this, but why let the facts get in the way of a good story?