Getting things right
by Gavin Schmidt, Real Climate, January 20, 2011
Last Monday, I was asked by a journalist whether a claim in a new report from a small NGO made any sense. The report was mostly focused on the impacts of climate change on food production – clearly an important topic, and one where public awareness of the scale of the risk is low. However, the study was based on a mistaken estimate of how large global warming would be in 2020. I replied to the journalist (and indirectly to the NGO itself, as did other scientists) that no, this did not make any sense, and that they should fix the errors before the report went public on Thursday. For various reasons, the NGO made no changes to their report. The press response to their study has therefore been almost totally dominated by the error at the beginning of the report, rather than the substance of their work on the impacts. This public relations debacle has lessons for NGOs, the press, and the public.
The erroneous claim in the study was that the temperature anomaly in 2020 would be 2.4 ºC above pre-industrial. This is obviously very different from the IPCC projections:
which show trends of about 0.2 ºC/decade, and temperatures at 2020 of around 1.0–1.4 ºC above pre-industrial. The claim is thus at least 1 ºC above what it should have been, and implied trends over the next decade an order of magnitude higher than otherwise expected.
How they made this mistake is quite instructive though. The steps they followed were as follows:
- Current CO2 is 390 ppm
- Growth in CO2 is around 2 ppm/yr, and so by 2020 there will be ~410 ppm
- They then calculated the CO2-eq to be 490 ppm.
- The forcing from 490 ppm with respect to the pre-industrial is 5.35*log(490/280) = 3 W/m2.
- Given a climate sensitivity of 3 ºC for 2 x CO2 (i.e., 3.7 W/m2), a forcing of 3 W/m2 translates to 3*3 / 3.7 = 2.4 ºC
The calculation is 3 (W/m2) * (3 ºC/2xCO2) / (3.7 (W/m2)/2xCO2) = 2.4 ºC. - gavin]
The first error is in misunderstanding what CO2-eq means and is used for. Unfortunately, there are two mutually inconsistent definitions out there (and they have been confused before). The first, used by policymakers in relation to the Kyoto protocol, relates the radiative impact of all the well-mixed greenhouse gases (i.e., CO2, CH4, N2O, CFCs) to an equivalent amount of CO2 for purposes of accounting across the basket of gases. Current GHG amounts under this definition are ~460 ppm, and conceivably could be 490 ppm by 2020.
However, the other definition is used when describing the total net forcing on the climate system. In that case, it is not just the Kyoto gases that must be included but also ozone, black carbon, sulphates, land use, nitrates etc. Coincidentally, all of the extra GHGs and aerosols actually cancel out to a large extent and so the CO2-eq in this sense is quite close to the actual value of CO2 all on its own (i.e., in IPCC 2007, the radiative forcing from CO2 was 1.7 W/m2, and the net radiative forcing was also 1.7 W/m2 (with larger uncertainties of course), implying the CO2-eq was equal to actual CO2 concentrations).
In deciding how the climate is going to react, one obviously needs to be using the second definition. Using the first is equivalent to assuming that between now and 2020 all anthropogenic aerosols, ozone and land use changes will go to zero. So, they used an excessive forcing value (3 W/m2 instead of ~2 W/m2).
The second mistake
has a bigger consequence:
is that they assumed that the instantaneous response to a forcing is the same as the long-term equilibrium response. This would be equivalent to a planet in which there was no thermal inertia – or one in which there were no oceans. Oceans have such a large heat capacity that it takes decades to hundreds of years for them to equilibriate to a new forcing. To quantify this, modellers often talk about transient climate sensitivity, a measure of a near-term temperature response to an increasing amount of CO2, and which is often less than half of the standard climate sensitivity.
has a bigger consequence:
is that they assumed that the instantaneous response to a forcing is the same as the long-term equilibrium response. This would be equivalent to a planet in which there was no thermal inertia – or one in which there were no oceans. Oceans have such a large heat capacity that it takes decades to hundreds of years for them to equilibriate to a new forcing. To quantify this, modellers often talk about transient climate sensitivity, a measure of a near-term temperature response to an increasing amount of CO2, and which is often less than half of the standard climate sensitivity.
It has to be acknowledged that people sometimes make genuine mistakes without having any desire to mislead or confuse, and that this is most likely the case here. It does no responsible organisation any good to have such a mistake in their material. It just leads to distractions from the substance of the report. The situation is serious enough that there is no need for exaggerated claims to produce headlines, just the plain unvarnished best guesses will be fine. It is likely that temperatures will reach 2.4 ºC at some point
in the next
this century, and so the calculated impacts are certainly relevant – just not in 2020.
in the next
this century, and so the calculated impacts are certainly relevant – just not in 2020.
Unfortunately, in this case the people involved did not decide to fix the errors that were pointed out, going so far as to have the PR person for the launch insist that the calculation was ok. That The Guardian journalist, Suzanne Goldenberg, took the time to check on the details is a credit to the press. The reaction can be put down to institutional inertia, combined with the fact that their scientific advisor was in hospital (and is 87). It would clearly have been much better to have had this properly peer reviewed ahead of time. To that end the AGU Q&A climate service or the Climate Science Rapid Reaction Taskforce (CSRRT) are invaluable resources for getting some quick scientific peer review.
Comment #35:
Comment #35:
I was probably the first to alert the NGO to their error when I read the embargoed study last Sat. I knew there was no way to get to +2.4C by 2020 and I’m just a journo ;]
I used the excellent Climate Science Rapid Reaction Taskforce (CSRRT) to confirm and told the NGO they’d got the science wrong. They said no. I got a couple more climate scientists involved. On Monday I suggested they withdraw or delay the report. They said they couldn’t.
I was pretty pissed off after 2/3 days of this. ‘Good intentions gone bad’ is what I called the story I wrote about all this http://bit.ly/giFzXD
Comment #39:
Comment #42:
Comment #39:
Gavin, here’s why I’m not as charitable as you in my assessment of the NGO’s conduct in this case.
We’re not talking about an innocent error that a sheepish NGO was willing to admit (are they even owning up to it now?). Based on what I’ve read at Steven Leahy’s blog and his related quote at The Science Journalism Tracker (which is reinforced by his comment #35 in this thread), it doesn’t seem a stretch for me to think the NGO went ahead fully aware that not all was right with their report.
Based on Stephen’s comment here, it sounds to me as if he didn’t try convincing them all on his own–he involved a number of climate journalists, as well. Still they balked.
What does that tell you? Were they just being incredibly obstinate? In denial? Or just maybe…did they think, what the hell. We’re going with it, truth be damned?
I don’t know what was in their minds, but they got some explaining to do.
[Response: Sure - they should definitely be called upon to explain their actions. But people can be stubborn - and people who aren't scientists often don't realise the importance of scientific criticism, so given info from people they don't know, while their own reviewer was in hospital and perhaps not completely on top of things, they took the non-decision to go ahead. Institutions often do dumb things like this (especially if they've been working on something for a year). But that is still not deliberately misleading the public. That would be unconscionable for a responsible NGO and goes against all experience I have ever had with groups like this. Any absolute claim to the contrary needs to be backed by more than just your instinct. - gavin]
Gavin:
But people can be stubborn – and people who aren’t scientists often don’t realise the importance of scientific criticism, so given info from people they don’t know, while their own reviewer was in hospital and perhaps not completely on top of things
Or perhaps the lay person who made the decision, being aware that the piece had been previously vetted by their expert, chose not to bother the 80-something scientist due to his being hospitalized, trusting that he had not boo-booed earlier.
Keith Kloor is quick to assume the worst where an innocent mistake seems likely – what would be the point of the NGO purposefully issuing something so clearly erroneous, knowing that knowledgeable scientists around the world would be quick to shoot it down?
Keith’s also quick to assume the best when it comes to folks on the denialist side of the fence …
[Response: Let's try not assume too much please... - gavin]