IPCC Reticence

The New York Times has an article pointing out that the IPCC’s response to uncertainty, at least based on leaked drafts of the upcoming report, is somewhat asymmetrical, favoring relative complacency:

In one case, we have a lot of mainstream science that says if human society keeps burning fossil fuels with abandon, considerable land ice could melt and the ocean could rise as much as three feet by the year 2100. We have some outlier science that says the problem could be quite a bit worse than that, with a maximum rise exceeding five feet.

The drafters of the report went with the lower numbers, choosing to treat the outlier science as not very credible.

In the second case, we have mainstream science that says if the amount of carbon dioxide in the atmosphere doubles, which is well on its way to happening, the long-term rise in the temperature of the earth will be at least 3.6 degrees Fahrenheit, but more likely above 5 degrees. We have outlier science that says the rise could come in well below 3 degrees.

In this case, the drafters of the report lowered the bottom end in a range of temperatures for how much the earth could warm, treating the outlier science as credible.

… Is it right to throw out bleeding-edge science in the one case while keeping it in the other?

I don’t always agree with everything Joe Romm says. But this time I agree with everything Joe Romm says.


  1. Maybe that is because real life data, the 17 year pause in warming, both makes the 5 foot sea level rise less likely and the 3 deg. C, or less, temperature rise more likely. A direct scaling of the actual model output and real temperatures reduces the climate sensitivity thus producing 3 deg. C, or less, by 2100. And if the temperature rises less, then the sea level should rise less. Rather simple actually - Based on real data, not models.

  2. The evidence really hasn't changed that much; while the reasons for the hiatus are not entirely sorted out, the background warming rate has changed very little. And there is no science without "models". See http://www.rmets.org/weather-and-climate/climate/has-global-warming-stalled , especially the graphic at the bottom of the page. You may be distracted by cherry picking, but IPCC should not be.

  3. I'm at a disadvantage not having seen the leaked report but can I assume they've changed the likely ECS range from 2-4.5 in AR4 to 1.5-4.5ºC? On a small point it seems to me this situation is exacerbated by giving these figures to the nearest multiple of 0.5. A 0.5 change looks fairly large but it could just mean the difference between 1.8 and 1.7.

    I can't agree with Justin Gillis' take on these issues. He suggests that mainstream science indicates a rise most likely in excess of 5ºF (~2.8ºC) but observation-linked studies reviewed in AR4 consistently found best estimates between 2 and 3ºC and, from what I've seen, most studies since then have indicated similar.

    Gillis seems to think the IPCC are trying to lean towards outlier very low estimates of <1.5ºC (I assume he's referring to the work of Lindzen, Spencer etc.) but I think it's more likely they're taking into account numerous mainstream studies (mostly 20thC energy balance methods) which have found best estimates of around 2ºC and given more weight to lower values in the pdf (e.g. Otto et al. 2013). As an aside, I suspect that many of these studies are inherently biased low but they are mainstream science. Given the evidence currently available it surely must be said that 1.5ºC appears to be about equally as likely as 4.5ºC.

  4. The 17 (since 1998? I make it just 16, maybe, but people do like to pile on) year pause in surface warming seems likely to be largely because it takes a while for the deeper ocean to absorb some of the heat, and some other mechanisms are in play. As far as I can see that makes the long tail of consequences worse rather than better. Once the ocean has absorbed enough heat it will become a contributor to the overall picture at a greater scale.

    So unless you have some way to stop time once things start to get really bad (not long now), you've got trouble. But by the time the prevaricating becomes obvious, it will be too late to fix things. Though I was fascinated to read today that Anthony Watts drives an electric car and has solar at his house. Seems he's wearing both belt and braces.

  5. Pingback: Another Week in the Ecological Crisis, September 15, 2013 – A Few Things Ill Considered

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