Arctic Sea Ice

The real AR5 bombshell

The whole fake skeptic propaganda effort disguised as 'leak' is boring me to death, but of course it's interesting to have a sneak peek preview of the IPCC Fifth Assessment Report (AR5) and see what they will have to say about Arctic sea ice. Geoff Beacon from the Brussels Blog already had a go at it, and found some frown inducing remarks. But for the sake of chronology I'm starting with first things first. 

From the Summary for Policymakers:

The average decadal extent of Arctic sea ice has decreased in every season since satellite observations commenced in 1979. The overall decrease in sea ice extent over the period 1979–2011 has been 3.9 [3.7 to 4.1] % per decade with larger changes occurring in summer and autumn (see Figure SPM.1). There is robust evidence of a decline in ice thickness, and in ice volume. The overall mean winter thickness has about halved between 1980 and 2009 {4.2.2}.

This, of course, is correct, and should give any sensible person pause. Given the magnitude of the event, the rate at which it is progressing (see long-term graphs), and the uncertainties with regards to possible consequences (in other words: we don't know what the worst case scenario could be), it's clear that just this short paragraph in the SMP (Summary for Policymakers) is enough to warrant some serious policymaking, which, I'm sorry to say, is not in favour of business-as-usual. Well done, IPCC!

But then, further on in the SMP, we get this:

There is very high confidence that climate models realistically simulate the annual cycle of Arctic sea ice extent, and there is high confidence that they realistically simulate the trend in Arctic sea ice extent over the past decades. {9.4.3}.

Very high confidence? I don't know about that, but before going to Chapter 9 let's first have a closer look at Chapter 4: Observations: Cryosphere, section 4.2.2.1:

Models are improving, but can they catch up?

All models are wrong, but some are useful, as the saying goes. However, when looking at how Arctic sea ice decline is modeled, one might be tempted to say that all sayings are useful, but some are wrong. To be fair, I should be the last person taking a piss at climate models. Hundreds of brilliant scientists, engineers and IT specialists are giving their best every day to make supercomputers come up with scenarios that project future changes. Unfortunately, there is no Planet B to experiment on.

But we have come to a point where fake skeptics show up in television programmes (such as last week's BBC Newsnight) and use modeled predictions for Arctic sea ice in the 2007 IPCC Fourth Assessment Report as an argument not to be worried about the disappearance of Arctic sea ice, because "none of them shows it melting before the year 2070 on a regular basis in the summer" (quote from UK Conservative MP Peter Lilley).

As always, they're not telling the whole story:

This image (taken from the Climate Crocks blog) comes from a GRL research paper by Stroeve et al. that was published in 2007, detailing how models that participated in the World Climate Research Programme Coupled Model Intercomparison Project Phase 3 (CMIP3) were doing compared to observations (red line). The 2011 dot was drawn in, based on NSIDC data on September 7th of last year. Commenter Tim took the liberty of drawing in the new 2012 record. This picture saves us the 1000 words needed to explain how off models are when it comes to matching observations, which essentially makes their projections worthless.

But as the Arctic sea ice cover has changed radically in just 6 years, so have new and improved models started a new round of simulations and projections for the Phase 5 project (CMIP5) for the next IPCC assessment report. And again, Dr. Julienne Stroeve and her colleagues from the NSIDC, NCAR and the Voeikov Main Geophysical Observatory in Russia, have taken a look at how these models are faring in a new GRL paper that was published three weeks ago in Geophysical research Letters: Trends in Arctic sea ice extent from CMIP5, CMIP3 and observations.

From the introduction: