Last week in New Hampshire, Jeb Bush said conservatives should “embrace science,” and the GOP needs to be the “party of science.” That was minutes after he embraced climate science denial.
“Look, first of all, the climate is changing,” Bush said. “I don’t think the science is clear what percentage is man-made and what percentage is natural. It’s convoluted. And for the people to say the science is decided on, this is just really arrogant, to be honest with you.”
Actually, it’s pretty easy to understand scientists’ best estimate of what fraction of recent warming is man-made — all of it. Jeb Bush asserts this issue is “convoluted,” but in fact it is so widely accepted that every major government in the world — including China, Russia, and Saudi Arabia — signed off on that finding almost two years ago.
I’m speaking of the findings of the IPCC’s 2013 Summary for Policymakers Fifth Assessment of the scientific literature. A key IPCC conclusion was that scientists are 95 to 100 percent certain humans are responsible for most of the added warming since 1950. They further explain that “the best estimate of the human-induced contribution to warming is similar to the observed warming over this period.”
To repeat, the best estimate is that humans are responsible for all of the warming we have suffered since 1950. Again, every major government in the world signed off on this finding, just like every other line in the Summary.
As for degree of certainty, the American Association for the Advancement of Science, the world’s largest general scientific society, explained last year, “The science linking human activities to climate change is analogous to the science linking smoking to lung and cardiovascular diseases.” I guess for Jeb the question of whether smoking is bad for your health is “convoluted” — and it’s “just really arrogant” for the Surgeon General and other medical professionals “to say the science is decided on.”
This IPCC finding wasn’t actually news even in 2013 — except to climate science deniers — since, of course, the IPCC is just a literature review. As we reported back in 2011, a study in Nature Geoscience concluded, “it is extremely likely that at least 74% of the observed warming since 1950 was caused by” humans.
So in fact scientists are 95 to 100 percent certain that at least some three quarters of the warming since 1950 is human-caused. Yes, that means the key IPCC conclusion is a watered-down version of the science, but that is how the IPCC rolls. When you have to satisfy pretty much every scientist (and then every major government) involved in the process with your choice of words, you end up with a “highly conservative organization,” as Stefan Rahmstorf, Head of Earth System Analysis at the Potsdam Institute for Climate Impact Research, told the New York Times in 2013. That means it “tends to produce a lowest common denominator on which a large number of scientists can agree.”
Gavin Schmidt, Director of NASA’s Goddard Institute for Space Studies, put together a graph to make the IPCC’s finding more visually understandable. Here is the relative likelihood that different percentages of global warming can be ascribed to human activity (“derived from Fig. 10.5 in IPCC AR5”):
For reference, “1.00” on the x-axis would mean climate change is 100 percent attributable to human activity. This graph peaks at about 1.10, or 110 percent.
But wait. How could 110 percent of the warming since 1950 be due to human activity? As Schmidt explained way back in 2009, “Over the last 40 or so years, natural drivers would have caused cooling.”
These cooling natural drivers include:
- In recent decades, volcanoes have released particles that partially block the sun and cool the planet slightly.
- Only recently have we come off “the deepest solar minimum in nearly a century,” which also cooled the planet slightly.
- The underlying long-term trend — driven largely by orbital changes — had been cooling (see Human-caused Arctic warming overtakes 2,000 years of natural cooling, “seminal” study finds).
In short, “human factors are most likely responsible for all the warming we’ve seen and then some (110%),” as environmental scientist Dana Nuccitelli put it in the UK Guardian.
Here’s the full video of Jeb:
Former Governor Bush apparently was against science before he was for it — or is it the other way around?