One of the main purposes of this blog is to save you time. As the Washington Post labels its TV columns on American Idol, “We watch … so you don’t have to.”
Nature has devoted much of its April 30 issue to “The Coming Climate Crunch” (subs. req’d). Sadly, after sitting through pretty much the whole thing, I can’t actually recommend anybody else see buy it. Any regular reader of this blog will learn very little new from the dozen or so articles — and the issue fails utterly to provide its readers with the two must-haves in any comprehensive coverage of the issue:
- A clear and specific understanding of the plausible worst-case scenario impacts facing the world post-2050 on our current emissions path.
- A clear and specific understanding of the core climate solutions, policies for their rapid deployment, and an understanding of why the total cost of action is so darn low — one tenth of a penny on the dollar.
What is particularly embarrassing for Nature, whose coverage of this issue has been second to none, is that they don’t even bother with #2 — even though they have a full article devoted to geo-engineering (a puff piece by someone who “now participates in scientific research on the topic”), another full article on adaptation, and yet another full article just on capturing CO2 from the air, which even one of its major proponents is quoted as saying is “the most expensive climate-mitigation technology.” What were the editors thinking?
The most useful thing in the entire issue is part of one of the figures in the article “Greenhouse-gas emission targets for limiting global warming to 2 °C” — which I’ve extracted and added to my must-have Powerpoint collection:
What is particularly “must-have” about this PPT is that it comes from a peer-reviewed article and clearly lays out the two choices:
- Halving 1990 levels of global greenhouse gas emissions by mid-century, which keeps total warming from preindustrial levels as close as possible to the “safe” level of 2°C.
- Staying anywhere near the business as usual path, which takes you to the worst-case IPCC scenario, A1F1 — or even worse than the worst (see U.S. media largely ignores latest warning from climate scientists: “Recent observations confirm “¦ the worst-case IPCC scenario trajectories (or even worse) are being realised” “” 1000 ppm).
Note that the results are quite in line with what the UK’s Hadley Center recently reported (see Hadley Center: “Catastrophic” 5-7°C warming by 2100 on current emissions path, but this is a better figure than Hadley’s, I think). I’d note that Hadley sees a median warming of 5.5°C on our current emissions path, but presumably that’s because they model warming beyond A1F1 (see also M.I.T. joins climate realists, doubles its projection of global warming by 2100 to ~5.5°C from preindustrial levels).
Bottom line: We are facing total warming of 5°C to 5.5°C by 2100.
What would be the impacts of 1000 ppm and 5°C warming or more by 2100? Probably the most disappointing article in the entire issue is by one of the country’s leading climate experts, “The worst-case scenario: Stephen Schneider explores what a world with 1,000 parts per million of CO2 in its atmosphere might look like.” Except that he doesn’t really explore that world.
For a long time the vast majority of climate scientists never modeled the impacts of high CO2 concentrations because they assumed humanity would never be so self-destructive as to allow them to occur. Today, however, a large and growing literature of high-emission-scenario climate impacts exists. You won’t, however, find that literature cited by Schneider, so the most specific thing he says is just to repeat the temperature forecasts of the other articles:
… under A1FI, so there is a 5-17% chance that temperatures will go up by more than 6.4 °C by 2100.
Many will argue that warming above 6.4 °C is unthinkable.
Actually, many will argue that warming above 3°C is unthinkable, and certainly warming above 4°C leads to incomprehensibly incalculable impacts by 2100, none of which Schneider lays out with any specificity. I try to summarize the literature in “An introduction to global warming impacts: Hell and High Water,” which notes that we’re looking at 3 to 7 feet of sea level rise by century’s end, followed by up to 1 to 2 inches a year rise for centuries, plus we turn up to one third of the planet or more into a Dust Bowl for centuries with projected loss (by the IPCC) of most species. But I digress.
The most useful article for the reader unfamiliar with the literature is probably, “Warming caused by cumulative carbon emissions towards the trillionth tonne.” They provide a very useful factoid, a very useful way for concisely talking about the required carbon target, which frankly I wish I had thought of myself:
Total anthropogenic emissions of one trillion tonnes of carbon (3.67 trillion tonnes of CO2), about half of which has already been emitted since industrialization began, results in a most likely peak carbon-dioxide-induced warming of 2 °C above pre-industrial temperatures, with a 5-95% confidence interval of 1.3-3.9 °C.
The fact that we can only “safely” emit another half a trillion tons of carbon this century is not news to the half dozen people who read the 2007 IPCC report closely (see “Nature publishes my climate analysis and solution“). Indeed, buried in the IPCC’s Working Group I Report on “The Physical Science Basis” of climate change (from early 2007) was this bombshell:
Based on current understanding of climate carbon cycle feedback, model studies suggest that to stabilise at 450 ppm carbon dioxide, could require that cumulative emissions over the 21st century be reduced from an average of approximately 670 [630 to 710] GtC to approximately 490 [375 to 600] GtC.
In short, we can only emit about a half a trillion metric tons of carbon this century to have a shot at 450 ppm (ending with virtually no emissions in 2100 since we’re at about 9 GtC now). And when you add that to the half a trillion tonnes we’ve already emitted, that gets you to the catchy “trillionth tonne” total.
Anyway, if you want to actually know how humanity is going to pull off this trick, you won’t find it in Nature. Try here instead: