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Back in April, The Evergreen State College invited me to speak at a TEDx event called “Hello Climate Change: Rethinking the Unthinkable.” Videos from the event are now online.

My talk was called “Climate change is simple.” I’m proud to say that I used only 17 of my allotted 15 minutes.

I’ve put an annotated version of my slideshow beneath the video, linking to sources and adding thoughts. The only thing I’ll say about the video itself is that I’ve always thought these things would be better with a soundtrack. If anybody out there on the web wants to make a mashup with it, add some good beats, be my guest.

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[UPDATE: Hey, someone pumped up the talk with music and visuals, just like I hoped! Go check it out.]

[youtube=http://www.youtube.com/watch?v=A7ktYbVwr90&w=470&h=264]

Okay, let’s walk through the slideshow, one or two at a time.

This talk was a consequence of me talking smack on Twitter. I said I could explain climate change in 15 minutes and was then invited to do so. D’oh!

The challenge I took on was to convey the gist of my “brutal logic of climate change” post in a reasonably short amount of time, using as little scientific jargon as possible. Just: there is a problem that calls for urgent action. Business-as-usual means disaster.

This is all gloom and doom — not even much humor. I know that turns people off or shuts them down. I know people need to feel a sense of hope and efficacy. I know — indeed, have recently been writing — that we need a vision of a sustainable future. But I needed to do my own version of “Danger Will Robinson!” Just to get it on the record.

Skeptics are fond of saying that “the Earth’s climate has always changed.” And that’s true. But some periods were more stable than others. Take the Holocene, for instance! Here’s the IPCC:

Interestingly, the Holocene appears by far the longest warm “stable” period (as far as seen from the Antarctic climate record) over the last 400 ky, with profound implications for the development of civilisation.

It was our profound good luck that everything in human history from the development of agriculture forward took place in period of relative climate stability. We are now in the process of pushing Earth systems outside those stable parameters — a massive, uncontrolled experiment undertaken in near-total ignorance of its timing and effects. Whee!

Here’s a reference:

The average temperature of the Earth’s surface increased by about 1.4°F (0.8°C) over the past 100 years, with about 1.0°F (0.6°C) of this warming occurring over just the past three decades.

The 2 degrees C target is an interesting topic in its own right. By now it’s been adopted by the E.U., the UNFCCC, the G8 — pretty much all the major emitters. But where did it come from? According to this paper (PDF), it ultimately traces back to a passing comment in a 1977 paper by, of all people, economist William Nordhaus. (WTF?) It was more or less an intuition on his part about the natural variability of temperature of the last 100,000 years. It was only later that the number became prescriptive rather than descriptive. It is now at the center of most climate policy analysis.

It’s important to remember that no specific number of degrees is “what science says” is dangerous. Picking a target involves not just the science of climate sensitivity but value judgments about risk and fairness.

On 2 degrees being too high:

Two degrees is what most climate scientists expect (or at least roughly in the center of a range of projections) if CO2 concentrations in the atmosphere reach 450 parts per million (ppm). James Hansen has become famous lately for warning that the climate is far more sensitive than commonly thought and 450 is way too high. His point is, rather than looking at what models project, we should look at the paleoclimate data from when concentrations were last that high. That data is considerably more grim than the model projections — seas were much higher, for one thing. In a paper last year, he and NATO colleague Makiko Sato warned:

Augmentation of peak Holocene temperature by even 1°C would be sufficient to trigger powerful amplifying polar feedbacks, leading to a planet at least as warm as in the Eemian and Holsteinian periods, making ice sheet disintegration and large sea level rise inevitable.

Hansen believes that 350 ppm is a more appropriate target (thus 350.org), which correlates roughly to 1.5 degrees C.

I probably shouldn’t have said, in my talk, that there’s a “growing consensus” around Hansen’s take on climate sensitivity. I think it’s probably still somewhat of an outlier in the climate science community. However, even scientists looking at the standard model projections have become leery of 2 degrees. Here’s what the scientists over at RealClimate said back in 2009:

We feel compelled to note that even a “moderate” warming of 2°C stands a strong chance of provoking drought and storm responses that could challenge civilized society, leading potentially to the conflict and suffering that go with failed states and mass migrations. Global warming of 2°C would leave the Earth warmer than it has been in millions of years, a disruption of climate conditions that have been stable for longer than the history of human agriculture. Given the drought that already afflicts Australia, the crumbling of the sea ice in the Arctic, and the increasing storm damage after only 0.8°C of warming so far, calling 2°C a danger limit seems to us pretty cavalier.

For more evidence that 2 degrees is too high, see this paper.

On the subject of 2 degrees C being out of reach, I refer you to my own “brutal logic of climate change mitigation” or to this paper, which says “there is now little to no chance of maintaining the global mean surface temperature at or below 2 degrees C.” Models showing temperature limited at that level contain all sorts of wildly positive assumptions.

Here’s the edition of the Royal Society journal that came out of the conference on 4 degrees C of warming. Read through it and see if you think “hell on earth” is an exaggeration. Desertification, water shortages, agricultural disruptions, rising sea levels, vanishing coral, tropical forest die-offs, mass species extinctions, oh my. Kevin Anderson, one of the lead scientists involved, was moved to say that “a 4 degrees C future is incompatible with an organized global community, is likely to be beyond ‘adaptation’, is devastating to the majority of ecosystems, and has a high probability of not being stable.” Double whee!

Speaking of not being stable:

This drought statistic isn’t actually from the 4 degrees conference; it comes from research by the U.K. Met Office. Technically it should say “severe drought.”

The IPCC warned of extinctions in the 40-70 percent range at 4 degrees. More recent research says maybe up to 80 percent. These projections on biodiversity loss are tentative and controversial. There’s a considerable amount of guess work. But that’s just the sort of complexity I wanted to avoid in the talk. Directionally, the trend is clear: we’re on track to wipe out a huge hunk of the world’s life forms.

The International Energy Agency’s World Energy Outlook 2011 warned that our current trajectory leads to as much as 6 degrees.

It’s important to note that 6 degrees is something of a worst case scenario — that’s what happens if we stay on a business-as-usual trajectory for the rest of the century. Scientists will tell you that this is implausible. But as I’ve argued before, they say so because they’re sure we’ll do something about it — that business-as-usual won’t continue.

After decades of tepid, notional progress in international climate negotiations, however, the idea that we’d be so super-duper stupid is not as ludicrous as it once seemed.

And here we come to the much-discussed “tipping point.” I know lots of scientists — and wonks/journos who like to talk like scientists — are squirmy about this notion. There’s not going to be one point when it’s suddenly “too late” to stop climate change. No one knows for certain when those thresholds might be passed, and if they are, we won’t know it happened until much, much later. Scientifically, the topic is complex and uncertain.

But my audience isn’t scientists, it’s the general public. The idea is to convey the basic shape of the situation, using concepts and language ordinary people can understand and remember. And there is plenty of scientific evidence that positive feedback loops exist, “state shift” thresholds exist, and at some point, enough of the former will pass the latter to make climate change, in aggregate, unstoppable. That’s a serious, existential threat to our species. We need to translate it into common language.

These slides probably aren’t entirely necessary, but I do think it’s worth emphasizing that, unlike most models and projections, the passage of time will not stop at 2100. Warming is going to continue after that.

The 12-degrees prediction is from a 2010 paper in the Proceedings of the National Academy of Sciences, by a couple of Australian scientists. It’s written up here:

“Much of the climate change debate has been about whether the world will succeed in keeping global warming to the relatively safe level of only 2 degrees Celsius by 2100,” said Professor Tony McMichael, from the Australian National University, in an accompanying paper published in the journal. “But climate change will not stop in 2100 and, under realistic scenarios out to 2300, we may be faced with temperature increases of 12 degrees or even more.”

Again, it’s not particularly important whether 12 degrees is precisely right — anything about the temperature in 2300 is highly speculative, of course — but it is important to convey that out-of-control warming could eventually render the world uninhabitable for human beings. It’s hard to even imagine 2300, but the people who will live then are real people, due some moral consideration.

Because Americans need this.

This is the essential message that needs to be conveyed to the public, and what I mean when I say “climate change is simple.” There are all sorts of interesting debates to be had about how best to proceed, what policies are most effective, what level of warming is tolerable … all that stuff is complicated and in need of democratic deliberation. But from the public’s point of view, the core fact here is that we have to do something or we’re screwed. Sitting this out is not an option, at least not a sane one.

Here’s my token “solutions” slide (I only had 15 … er, 17 minutes!), and it’s really not a solution at all as much as an aspiration against which solutions will be judged. For more on those numbers, see here and here.

This figure is from the IEA as well, but again, the specifics aren’t as important as the structure of the problem. Delay raises the inevitable costs. Solutions are “expensive,” but not nearly as expensive as inaction.

This slide didn’t make it into the video, but it got a little laugh at the end. A nervous, shell-shocked laugh, but a laugh nonetheless. Wheee…