CREDIT: John Cook, Skeptical Science


The Senator is right: ‘Humans are entirely the cause’ of recent warming...

Last week, Energy Secretary Rick Perry lost his cool when Sen. Al Franken (D-MN) informed him that scientists have determined “humans are entirely the cause” of recent warming.

Perry is so used to denying the overwhelming consensus that humans are responsible for most recent warming, he simply couldn’t get his head around the fact that scientists’ best estimate is humans are actually responsible for all recent warming.

Franken, I think, has hit on a winning message — one that is also factually accurate, as the latest scientific literature makes clear.

Several years ago, when the world’s leading climate scientists figured out that humans were responsible for all recent warming, they decided to focus instead on the very high statistical likelihood that humans are the main cause of warming. Here’s the highlighted — and much-quoted finding — from their 2013 assessment of the science: “It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century.” (Emphasis in original, with “extremely likely” defined as 95 to 100 percent likelihood).

Even Fox News anchor Chris Wallace used this quote to debunk EPA chief Scott Pruitt, who had falsely claimed that CO2 is not “a primary contributor to the global warming that we see.” Fox made a graphic from it:

Screenshot of FoxNews graphic April 2, 2017.

Here’s the problem with focusing on the chances human activity are responsible for most of the warming — rather than the best estimate that humans are responsible for all of it: It became easier for unscrupulous deniers to pretend there is a serious debate over exactly how much warming comes from human activity. There isn’t, but this “debate” has become a key talking point for deniers.

Perry used that approach on CNBC. And he repeated it again at the White House press briefing on Tuesday, when he said humans do have some effect, but “how much of an effect is what is at debate here.”

That’s why Perry got so upset when Franken said “humans are entirely the cause” of recent warming, sputtering out “I don’t believe it” and “I don’t buy it.”

If human activity is entirely the cause of recent warming — and the best science says it is — then obviously the entire solution must involve changing human activity, switching from dirty fossil fuels to clean energy, and so on. But those solutions are precisely what deniers like Perry oppose.

So when Franken reminded him this was the finding of a “red team” of climate science skeptics funded by conservative petrochemical billionaires Charles and David Koch, Perry responded angrily: “To stand up and say that 100 percent of global warming is because of human activity, I think on its face, is just indefensible.”


For the record, it is the opposite of indefensible. In their 2013 assessment, the top climatologists concluded that “the best estimate of the human-induced contribution to warming is similar to the observed warming over this period.” Translation: The best estimate is that humans are responsible for all of the warming we have suffered since 1950. That finding was signed off on by all the world’s major governments.

Unfortunately, the 2013 assessment buried this bombshell at the end of a paragraph on page 12 of their summary report in very dry language. And so most science communicators and journalists naturally focused on the finding that there’s a 95 to 100 percent likelihood most of the warming is due to human activity.

But Franken’s framing is simpler and more compelling — while also being factually accurate.

Finally, some commenters have tried to argue that Franken made a science mistake in this exchange. It is true that when he quoted a July 2012 op-ed by the head of the Koch-funded team, Franken ellipsized the word “almost” from the full quote “Humans are almost entirely the cause.

But the op-ed itself points out that the team found a rise in the temperature of the earth’s land of 2.5°F over the past 250 years, including a 1.5°F rise in the most recent 50 years and found that “it appears likely that essentially all of this increase results from the human emission of greenhouse gases.”

Their peer-reviewed paper concluded, “all of the long-term (century scale) trend in temperature can be explained by a simple response to greenhouse gas changes.” And it includes this chart:



The decadal land surface temperature from the BerkeleyEarth average, compared to a linear combination of volcanic sulfate emissions and the natural logarithm of CO2. Credit: Berkeley Earth

Moreover, as noted earlier, when you look at all of the latest science, “the best estimate of the human-induced contribution” to recent warming (since 1950) is “all of it,” as Skeptical Science sums it up (see top chart).

Kudos to Al Franken for pointing out and repeating this winning message.

Go to the profile of Joe Romm

Joe Romm

Dr. Joe Romm is Founding Editor of Climate Progress, “the indispensable blog,” as NY Times columnist Tom Friedman describes it.


original story HERE


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