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:

1. A clear and specific understanding of the plausible worst-case scenario impacts facing the world post-2050 on our current emissions path.
2. 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:

1. 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.
2. 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:

• How the world can (and will) stabilize at 350 to 450 ppm: The full global warming solution (updated)
• An introduction to the core climate solutions

This must-have slide (click to enlarge) comes from a 2005 study, “Regional vegetation die-off in response to global-change-type drought.” I first saw it in a powerful 2005 presentation by climatologist Jonathan Overpeck, “Warm climate abrupt change–paleo-perspectives,” that concluded “climate change seldom occurs gradually.”

Overpeck noted that the 2005 study, together with the recent evidence that temperature [in red] and annual precipitation [in blue] are headed in opposite directions in the U.S. Southwest, raises the question of whether we are at the “dawn of the super-interglacial drought.”

Before explaining why I like this slide and how it shows the future of extreme weather, I need to review the conclusion of the study, which was led by the University of Arizona, with Los Alamos National Laboratory and the U.S. Geological Survey:

Global climate change is projected to yield increases in frequency and intensity of drought occurring under warming temperatures, referred to here as global-change-type drought….

Our results are notable in documenting rapid, regional-scale mortality of a dominant tree species in response to subcontinental drought accompanied by anomalously high temperatures.

The researchers examined a huge three-million acre die-off of vegetation in 2002-2003 “in response to drought and associated bark beetle infestations” in the Four Corners area (Arizona, New Mexico, Colorado, and Utah).

This drought was not quite as dry as the one in that region in the 1950s, but it was much warmer, hence it was a global-warming-type drought. The recent drought had “nearly complete tree mortality across many size and age classes” whereas “most of the patchy mortality in the 1950s was associated with trees [greater than] 100 years old.”

The study concluded:

Our results quantify a trigger leading to rapid, drought-induced die-off of overstory woody plants at subcontinental scale and highlight the potential for such die-off to be more severe and extensive for future global-change-type drought under warmer conditions….

It should be obvious that warm-weather droughts are worse than cooler-weather droughts — but if it weren’t, this study shows they are.

The slide depicts annual precipitation and annual temperature in the Four Corners area (i.e. the heart of the U.S. Southwest). It shows that over at least the past 70 years, and presumably much longer, annual precipitation and annual temperature are not particularly correlated. You can have warm droughts and you can have cool droughts.

The warning of the slide to humanity is clear: All future droughts are going to be warm-weather droughts — and if we don’t change course soon — they will become hot weather droughts, then hellish droughts.

Remember, on our current emissions path, the planet is poised to be 5.5°C to 7°C warmer by 2100. The climate models predict that in mid-latitudes land masses (i.e. inland U.S), warming could be 50% higher. That would be 8°C to 10°C warmer — which is way, way off that chart.

And even the Bush administration acknowledged the scientific literature says that on our current emissions path, the SW is poised to get much drier (see “US Geological Survey stunner: SW faces “permanent drying” by 2050“). And that drought will likely last a long, long time (see NOAA stunner: Climate change “largely irreversible for 1000 years,” with permanent Dust Bowls in Southwest and around the globe).

So we have what Overpeck calls “the super-interglacial drought.” Australia, which is more sensitive to initial climate change than the SW and thus a canary in the coal mine, calls it the “permanent dry” or perhaps “collapse.”

Others might just call it a desert.

But before you get the permanent desertification, you get warm-weather droughts, the “global-change-type drought,” and that is the future of extreme weather this century.

Note: I started this new feature and a new category here for Must-have PowerPoint Slides last August (see “Must have PPT #1: The narrow temperature window that gave us modern human civilization“). I haven’t done a good job so far of building out the full set of PPTs, but I will endeavor to add a couple of month.

The slide is a must-have because it captures the risk we are taking while also providing a quick visual rebuttal to a very common denier talking point, one that NASA administrator Michael Griffin of all people repeated last year (see “And the Moon is Made of Green Cheese“):

To assume that [global warming] is a problem is to assume that the state of Earth’s climate today is the optimal climate, the best climate that we could have or ever have had and that we need to take steps to make sure that it doesn’t change…. I guess I would ask which human beings — where and when — are to be accorded the privilege of deciding that this particular climate that we have right here today, right now is the best climate for all other human beings. I think that’s a rather arrogant position for people to take.

Seriously! Needless to say, his employee, James Hansen rightly called those remarks “ignorant and arrogant.” He might have added “suicidal.”

So I had to have this slide after I saw it in a recent presentation from my friend Bob Corell, chair of the Arctic Climate Impact Assessment and now Director of Global Change Programs at the Heinz Center.

And it’s not just Griffin pushing this nonsense. One of the Cato Institute climate experts currently debating the online, Indur Goklany, just advanced the following argument against my call to stabilize at 450 ppm or less:

… there is no guarantee that stabilizing CO₂ at 450 ppm would optimize human or environmental well-being. For all we know, stabilizing at 750 may be more optimal.

For all we know, Cato Institute might be funded by manufacturers of flood levees and desalination plants. Seriously, where does Cato find these guys? You can read my full reply to his absurd and disingenuous arguments here (”Goklany Okay with 250-Foot Sea-Level Rise“). I used Correll’s figure in the reply, which was a major inspiration for me to finally get off my butt and start this feature. [Note to self: Actually, you stayed on your butt the entire time you wrote this post.]

One key explanatory background note if you use the slide: The IPCC forecast of a total of 2°C to 3°C is based on stabilizing atmospheric concentrations of CO2 around 550 ppm (a doubling from pre-industrial levels of 280), up from 385 today. The “band of uncertainty” involves the uncertainty about the climate sensitivity to a doubling of CO2 (absent the slow feedbacks). But as I have noted here before, the longer-term climate sensitivity to a doubling is probably much higher (see “Another “Must Read” from Hansen: ‘Long-term’ climate sensitivity of 6°C for doubled CO2“). In any case, we are headed to much more than 550 ppm this century. As the IPCC’s latest assessment makes clear, anything other than a sharp and rapid reversal in greenhouse gas emissions trends risks warming this century of 4°C or more (see “Is 450 ppm politically possible? Part 0: The alternative is humanity’s self-destruction“).

More about the Must-have PPT Slides Feature

I have accumulated a lot of good slides and figures over the years, but I don’t give many talks anymore for a lot of reasons. Air travel sucks, it generates a lot of carbon, it takes me away from my daughter, and talks to even a few hundred people aren’t a good use of my time because this blog reaches more than ten times that number of people every day.

So the point is, my slides mostly go to waste, and I hope some of you out there who are giving talks or blogging or just emailing friends can use the figures. I’ll try to post one a week. I certainly welcome readers posting their favorite slides or figures, and I may feature the best ones.

I have named the category “Best PPTs” so it would appear at the top of the category list.