Sunday, August 15, 2010

KVMR science and the climate threat - calibration

See Aug 20 update below, on meaningful vs. misleading assertions; and Aug 24 update below it, on what sensitivity can't tell us. Also see the Soundings host's response.

KVMR's biweekly science show Soundings has been extremely light on climate coverage, and what coverage it's done has skirted the all-important question, "how serious is climate change likely to get under Business As Usual, and how should we go about deciding what actions to take and when?"

In part this is by design; since the show avoids policy, it won't address the second part of this question.

But science (sans policy) can shine a light on the first, "how serious is it likely to get" part, which climate scientists address (but see update below) by using various approaches to estimate the earth's climate sensitivity - "the global equilibrium surface warming after a doubling of atmospheric CO2 concentration". The lower the value, the less of a threat climate change presents.

We can't know this value for sure ahead of time, so it's typically expressed as a likely range.
Sounding's host has asserted that this "likely" range is low - that climate scientists consider a 3C "scorched earth" value to be at the extreme upper end of the range; reportedly this view is based on reading the scientific literature and talking to the scientists themselves.

I disagreed with this assertion, based on my own reading (not of the literature itself, but of science-aligned climate blogs and of (science-aligned) SkepticalScience - to my mind, a more reliable way to inform myself), and when I asked for some names and some scientific papers supporting the assertion, to check them out myself (link), was given (only) the review article "The equilibrium sensitivity of the Earth’s temperature to radiation changes" (Knutti and Hegerl 2008).

But from reading just the first few sentences of this paper's abstract, I don't see how anyone could conclude that climate scientists are saying 3C is "the extreme upper end of the range" - quite the contrary: (emphases added)
"Various observations favour a climate sensitivity value of about 3 °C, with a likely range of about 2–4.5 °C. However, the physics of the response and uncertainties in forcing lead to fundamental difficulties in ruling out higher values. The quest to determine climate sensitivity has now been going on for decades, with disturbingly little progress in narrowing the large uncertainty range.
Can someone explain to me, how this could support "3C is at the extreme upper limit of the likely range"? Are there other credible sources that do say that?
Sources please.

Perhaps relevant - Jonah Lehrer's We Are All Talk Radio Hosts
Aug 20 update: OK, I've learned an important lesson here, which I will now pass on to you -

First, on the likely sensitivity range, I stand somewhat corrected; a source I respect, who knows what he's talking about, is saying (link) "we think we have a good grip on this [climate sensitivity] number. It's probably between 2.5 C and 3.0 C per doubling, pretty much certainly between 1.5 and 5 C."

- just as the Soundings host asserted, "3.0C is at the extreme upper end of the likely range". [ Update: although he was saying 1-3C, not 2.5-3C, so a) it wasn't even 'narrowly' right; but b) it also wasn't the propaganda attempt I infer below.]

But that statement sure looks misleading and propagandistic - by failing to mention that
the "likely range" is so narrow - just half a degree C - it makes a near-3C increase sound unlikely.

A good test for its propaganda quality is to try out the equivalent-opposite statement.
Suppose instead we said, "a 2.5C (5 degrees F) increase is at the extreme lower end of the likely range"; then what would the listener conclude?

Answer: that we're toast.

So why propagandize? What's the rationale for giving only the piece that, standing on its own, underplays the severity of the problem?
(I've asked (and I've notified Soundings' host of this post), and will report back when/if I get a response.)
Aug 24 update: no response yet. I need to give you an important piece of the big-picture puzzle, that I'd overlooked - above I'd said that
climate scientists address threat of climate change by estimating how much the earth will warm, but you need to realize that's a very imperfect measure - as Michael Tobis points out in his big-picture dialogue (part I, part II; well worth your time), what we're doing is destabilizing the climate, and warming is just one part of that. We *don't* know how much warming will be associated with throwing the climate system off kilter - and from what we've seen this summer, the destabilization could start a lot earlier than we'd thought.

It's happening in *our* lifetimes.

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