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Saturday, February 03, 2007

Hung Up Over the Wrong Numbers


Our society has a love of numbers. If something can be measured, it will be, no matter how meaningless the figures are. Ever since I discovered my dad's copy of Darrell Huff's How to Lie With Statistics in my teens I've been fascinated by the misuse of meaningless measures and facile facts.

So it was interesting to read Roger Pielke Jr's commentary on The Economist's recent feature on climate change. Pielke reminds us that what has to be stabilised is not the levels of CO2 emissions, but the levels of CO2 in the atmosphere. And to do that at levels which will not be catastrophic is no easy task.

Socolow and Pacala's famous "wedge graphs" make this fundamental mistake, which leads them to weak conclusions.

Perhaps that's why politicians are so keen to talk of stabilising emissions at 199x levels. Choose your year, it doesn't really matter, it's still an easy but irrelevant target, despite all the government protests over the Kyoto Protocol being too difficult to attain.

The IPCC 4th Assessment Summary for Policymakers came out yesterday. On page 10 the IPCC scientists state:

"even if the concentrations of all greenhouse gases and aerosols had been kept constant at year 2000 levels, a further warming of 0.1ºC per decade would be expected."

And on page 13:

"Both past and future anthropogenic carbon dioxide emissions will continue to contribute to warming and sea level rise for more than a millennium".

Baer and Athanasiou, in a chilling discussion about the European Union's CO2 level stabilisation targets of 450 parts per million (current CO2 concentrations are 380ppm), which corresponds to an estimated 2ºC temperature rise, argue that "even if greenhouse-gas concentrations stopped rising today, we might still already be committed to a temperature increase greater than 2ºC." And they add that "two degrees is already a compromised target, one with which we've already negotiated away thousands of species and, probably, millions of lives."

Little room for complacency there.

David Archer over at realclimate.org also points out another "wrong number":

"Most of the climate change community, steered by Kyoto and IPCC, limit the scope of their consideration to the year 2100. By setting up the problem in this way, the calculation of a safe CO2 emission goes up by about 40%, because it takes about a century for the climate to fully respond to rising CO2. If CO2 emission continues up to the year 2100, then the warming in the year 2100 would only be about 60% of the "committed warming" from the CO2 concentration in 2100. This calculation seems rather callous, almost sneaky, given the inevitability of warming once the CO2 is released. I suspect that many in the community are not aware of this sneaky implication of restricting our attention to a relatively short time horizon."

junkscience.com isn't too happy about political influence on the IPCC scientists, and has leaked the drafts of the full 4th Assessment reports.

realclimate.org counters these claims and provides ongoing excellent coverage and debate.

The radiative forcing effects of atmospheric CO2 have been known for almost 150 years thanks to the pioneering scientific work by John Tyndall.

If only we'd taken Arrhenius seriously back in 1896.

Postscript, June 30th, 2009

Lou Grinzo is asking similar questions about that 2 degrees Celsius number. He has links to a couple of interesting discussions about the EU's adoption of the 2 degree number, and is worth a read. These days I'm inclined to believe that even a 1 degree Celsius temperature increase is too high a figure.

PPS, December 1st 2011 (#cop(out)17 update)

Lou posted an update on the 2 degree C question in December 2010. The figure comes from René Dubos' and Barbara Ward's book "Only One Earth", published in 1972. He observes: "This is the earliest discussion I could find of 2°C being used in any way similar to the “guardrail”, and it only strengthens my belief that we’ve grandfathered in this guideline and would come up with a lower number if we started from scratch with our current understanding of the Earth System." Quite!

PPS, December 5th, 2011

Grist's David Roberts has a great post up today entitled "The brutal logic of climate change", about how 1°C is the new 2°C, and why urgent action is needed now.

PPS, February 28th, 2013

Lou Grinzo has kindly resurrected his June 2009 2 Degrees blog post which had mysteriously evaporated. I'd missed his Two degrees, too much post from December 2009. Give it a read too.

PPS, December 10th, 2014

A rant of mine on Twitter today about what degree of confidence we have in 2 degrees being safe led to a couple of responses:

Chris Shaw shared his paper published in Global Environment Change last year, "Choosing a dangerous limit for climate change: Public representations of the decision-making process", which is a far better discussion of the subject than I'll ever produce.

"While public discourses maintain a fixed use of the two degree limit, an evolving body of climate science is highlighting how unsafe two degrees of warming will be. Existing two degree discourses, in employing an erroneous reliance on science to support claims of a two degree dangerous limit, exhibit few deliberative qualities. Any attempt to develop a more participatory policy discourse around climate change might begin with a more honest depiction of the limits to scientific definitions of dangerous climate change."

And Aaron pointed us at an article by Kevin Anderson from 2012, "‘Climate Change: going beyond dangerous" (.pdf).

"If the logic of defining 2°C impacts as dangerous is to hold, the more recent impact analysis suggests 2°C represents the threshold between dangerous and extremely dangerous, rather than between acceptable and dangerous climate change. Certainly, it could reasonably be argued that 1°C rather than 2°C should become the de facto appropriate target. If one accepts the rationale of safeguarding against dangerous climate change it is difficult to argue against a 1°C goal from a scientific point of view."

Posted by Phil at 1:12 PM
Edited on: Wednesday, April 01, 2015 10:29 PM
Categories: Comment, Environment, Waffle