On 1 May 2007, the online edition of Geophysical Research Letters will publish a study by a combined team from the National Center for Atmospheric Research (NCAR) and the University of Colorado’s National Snow and Ice Data Center (NSIDC). 
This study report will show, in yet another way, how the Intergovernment Panel on Climate Change (IPCC) report is overly optimistic and is likely understating the risks and impact of Global Warming. In this case, the to-be-published study: ‘
Arctic Sea Ice Decline: Faster Than Forecast?
This study examined the 18 different computer models used by the IPCC and compared the models’ predictions about Artic sea ice coverage with actual data.
The study team
compared model simulations of past climate with observations by satellites and other instruments. They found that, on average, the models simulated a loss in September ice cover of 2.5 percent per decade from 1953 to 2006. The fastest rate of September retreat in any individual model was 5.4 percent per decade. (September marks the yearly minimum of sea ice in the Arctic.) But newly available data sets, blending early aircraft and ship reports with more recent satellite measurements that are considered more reliable than the earlier records, show that the September ice actually declined at a rate of about 7.8 percent per decade during the 1953-2006 period.
“This suggests that current model projections may in fact provide a conservative estimate of future Arctic change, and that the summer Arctic sea ice may disappear considerably earlier than IPCC projections,”
In the graphic, the red line shows the actual Artic ice melting. The blue area represents the range of melting predicted within the 18 different IPCC climate models.
In short, Artic ice melting (ice-free Artic) looks to be “30 years ahead of schedule”.
A critical gap in IPCC modeling is the basic absence of “positive feedback cycles” …
The Arctic is especially sensitive to climate change partly because regions of sea ice, which reflect sunlight back into space and provide a cooling impact, are disappearing. In contrast, darker areas of open water, which are expanding, absorb sunlight and increase temperatures. This feedback loop has played a role in the increasingly rapid loss of ice in recent years, which accelerated to 9.1 percent per decade from 1979 to 2006 according to satellite observations.
Now some might take this report in the following way:
“Well, see, the models are wrong. We don’t know enough. We must study the problem more before we take action. Let’s pay the scientists some money and go back to other things.”
This type of thinking and argument, which has been so prevalent in Global Warming Skeptic/Denier rhetoric, sabotages our ability to move toward a saner energy policy. In fact, this data should be driving us (US) toward more aggressive action.
It is correct: we don’t know enough. And, in this case, it looks like what we don’t know might very well kill us faster …
42 responses so far ↓
1 Arthur Smith // May 3, 2007 at 9:59 pm
J Frey
Read the IPCC report. I particularly recommend the Technical Summary. It answers every single one of your complaints in detail with references to the full report which further has references to the original literature. For example, on the 150 year temperature record, there is extensive analysis on how reliable that is – the complaints about “heat island” effects are demonstrated to have a negligible effect on the temperatures used in analysis, for instance. And there is extensive discussion of the models. If the models “depend on the assumptions” of the modelers, then you would expect there to be plenty of models from people who assume that global warming will have no effect (because there are a huge number of people who seem to still believe that, and there were many scientists who believed that too until a few decades ago). But there are, in fact, no detailed numerical climate models that match those assumptions – every model shows a temperature response of at least 1.5 degrees C to doubling CO2, and the many other consequences that have been discussed as well.
Yes some results are uncertain – the IPCC report goes into extensive detail to quantify uncertainties, and reports these in an extremely clear manner: some things are “likely”, “very likely”, “almost certain” etc. depending on the percent likelihood of the condition in question, based on the data we have to this point. That’s a translation of the “noise in the data” into quantifiable statements of facts. It’s not that hard to do.
And no, humans have not doubled CO2 yet. We’re up by 40% from pre-industrial levels. Also, the response to doubling that is reported is a long-term response; the “transient” (short-term) response is expected to be slightly lower because of delays from things like the heat capacity of the oceans. The temperature rise so far of about 1 degree C is exactly on the order of what the models expect for this transient response to a half-doubling, if the full response is about 3 degrees. Look at the numbers, read the report yourself. It’s not that hard to understand.
2 Arthur Smith // May 3, 2007 at 10:13 pm
Oh, you also mentioned the sea level rise issue. The mean for the sea level rise estimate did indeed decrease – but that was almost entirely because the IPCC removed from the new report estimates of ice-sheet melting acceleration which had raised the upper-bound in the third report. There’s actually strong evidence for acceleration in melting of the major ice sheets, but instead the main estimate in the new report was a “Model-based range excluding future rapid dynamical changes in ice flow” as you can see in table TS.6 (p. 70 of technical summary).
There were also a few technical changes – the date range for the estimates is different, and the number of standard deviations used to describe the range was different. As the fourth report states in reference to the third report (TAR) – “The TAR would have had similar ranges for sea level projections to those in this report if it had treated the uncertainties in the
same way.” (p. 70).
So, again despite misleading media reports, there was actually no change in the sea level projections in the new report from the 2001 version.
I wonder why various media outlets insist on announcing that the IPCC has reduced their estimates for things, when that’s simply not true?