Why increasing CO2 is a significant problem — in six easy steps

NASA scientist Gavin Schmidt continues to do terrific blogging at RealClimate explaining climate science and the immateriality of the illegally hacked e-mails to our broad understanding of human-caused global warming.  That, of course, is why the anti-scientific ideologues are going after him so hard (see “Competitive Enterprise Institute to sue RealClimate blogger over moderation policy“).

He was asked recently on RC, “what percentage of global warming is due to human causes vs. natural causes?”  I’m posting his reply here because it’s a good answer and frankly much clearer than the one science advisor John Holdren gave at today’s House hearing to an almost identical question — though I thought Holdren and Lubchenco were both terrific, especially in their opening statements, and I hope to get those videos up as soon as they are available.  Schmidt explained:

Over the last 40 or so years, natural drivers would have caused cooling, and so the warming there has been … is caused by a combination of human drivers and some degree of internal variability. I would judge the maximum amplitude of the internal variability to be roughly 0.1 deg C over that time period, and so given the warming of ~0.5 deg C, I’d say somewhere between 80 to 120% of the warming. Slightly larger range if you want a large range for the internal stuff.

Schmidt has a new post today on the emails, in which he urges people to read a 2007 post that provides  “an easy-to-understand explanation for why increasing CO₂ is a significant problem without relying on climate models,” which I am reposting below: Read more

E-mails “highlight yet again the harassment that denialists inflict on some climate-change researchers.”

Stolen e-mails have revealed no scientific conspiracy, but do highlight ways in which climate researchers could be better supported in the face of public scrutiny.

The e-mail archives stolen last month from the Climatic Research Unit at the University of East Anglia (UEA), UK, have been greeted by the climate-change-denialist fringe as a propaganda windfall (see page 551). To these denialists, the scientists’ scathing remarks about certain controversial palaeoclimate reconstructions qualify as the proverbial ‘smoking gun’: proof that mainstream climate researchers have systematically conspired to suppress evidence contradicting their doctrine that humans are warming the globe.

This paranoid interpretation would be laughable were it not for the fact that obstructionist politicians in the US Senate will probably use it next year as an excuse to stiffen their opposition to the country’s much needed climate bill. Nothing in the e-mails undermines the scientific case that global warming is real “” or that human activities are almost certainly the cause. That case is supported by multiple, robust lines of evidence, including several that are completely independent of the climate reconstructions debated in the e-mails.

First, Earth’s cryosphere is changing as one would expect in a warming climate. These changes include glacier retreat, thinning and areal reduction of Arctic sea ice, reductions in permafrost and accelerated loss of mass from the Greenland and Antarctic ice sheets. Second, the global sea level is rising. The rise is caused in part by water pouring in from melting glaciers and ice sheets, but also by thermal expansion as the oceans warm. Third, decades of biological data on blooming dates and the like suggest that spring is arriving earlier each year.

Denialists often maintain that these changes are just a symptom of natural climate variability. But when climate modellers test this assertion by running their simulations with greenhouse gases such as carbon dioxide held fixed, the results bear little resemblance to the observed warming. The strong implication is that increased greenhouse-gas emissions have played an important part in recent warming, meaning that curbing the world’s voracious appetite for carbon is essential (see pages 568 and 570).

So begins, “Climatologists under pressure,” an important and lengthy editorial in tomorrow’s Nature (subs. req’d, reprinted below), the highly respected British scientific journal, which is among the few journals “that still publish original research articles across a wide range of scientific fields,” including climate science.  [I am leaving the links in the editorial, but they require a subscription.]

For all the disinformation that the deniers are pushing because of these emails — lapped up mostly by people who never understood or believed the science to begin with, I actually think this affair is an opportunity for the too-reticent, too-insular scientific community to explain climate science to the broader public, which Phil Jones and UEA chose not to do, but which many others have started doing (see Climate science statement from the Met Office, NERC and the Royal Society: It’s the hottest decade on record and “even since the 2007 IPCC Assessment the evidence for dangerous, long-term and potentially irreversible climate change has strengthened”).

Indeed, besides RealClimate and CP’s posts (at the end), I’d recommend: Read more