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October 30, 2006

Stern Report

OK, the Stern Report is out now.

700 pages to read. Wonder if I'll find anything interesting?

Chapter 1

Oops! Line three:

Most climate models show that a doubling of pre-industrial levels of greenhouse gases is very likely to commit the Earth to a rise of between 2 – 5°C in global mean temperatures.

Nope, climate sensitivity is now known to be 1.5 to 4.5 with 3 as the most likely value for a doubling of CO2 concentrations.

Page 3:

The Third Assessment Report (TAR) of the Intergovernmental Panel on Climate Change (IPCC)1 in 2001 was the last comprehensive assessment of the state of the science. This chapter uses the 2001 report as a base and builds on it with more recent studies that embody a more explicit treatment of risk.

Err, why not use TAR IV? We all saw drafts of it back in the spring: why use 'recent research' that hasn't been tested, when there's a better version of the state of the (checked) art available to you?

These studies support the broad conclusions of that report, but demonstrate a sizeable probability that the sensitivity of the climate to greenhouse gases is greater than previously thought.

Err, no: the estimates of climate sensitivity have fallen, not risen.

As anticipated by scientists, global mean surface temperatures have risen over the past century. The Earth has warmed by 0.7°C since around 1900 (Figure 1.3).

As anticipated? Tosh! Come on now, where's the studies by scientists from 1906 stating that temperatures would rise? No, what you're actually meaning is that scientists have noted a temperature rise and have spent the last couple of decades desperately trying to work out why, what's been happening. Please, if this is going to be the major report on the subject can we at least get these things right?

Page 6:

It is now clear that, while natural factors, such as changes in solar intensity and volcanic eruptions, can explain much of the trend in global temperatures in the early nineteenth century, the rising levels of greenhouse gases provide the only plausible explanation for the observed trend for at least the past 50 years.

Well, sorta. The cooling after 1940 or so needs to be explained. That's probably the result of the burst of dirty industrialization in the period, throwing up more aerosols and particularates that cool. As we then worked, in subsequent decades, to clear the air, their masking effect on the CO2 was removed. As above, if this is going to be the be all and end all of reports, best to get it right.


Taking into account the rising levels of aerosols, which cool the atmosphere,1

Mentioned in the next para but not linked to the mid century cooling still.

higher climate sensitivities cannot be excluded; and secondly, it allows a more explicit treatment of risk. For example, eleven recent studies suggest only between a 0% and 2% chance that the climate sensitivity is less than 1°C, but between a 2% and 20% chance that climate sensitivity is greater than 5°C19.

That isn't what I've seen. Here's a description of a paper on climate sensitivity which contradicts that.

Sea level rises:

Sea levels will respond more slowly than temperatures to changing greenhouse gas concentrations. Sea levels are currently rising globally at around 3 mm per year and the rise has been accelerating55. According to the IPCC TAR, sea levels are projected to rise by 9 - 88 cm by 2100, mainly due to expansion of the warmer oceans and melting glaciers on land.56 However, because warming only penetrates the oceans very slowly, sea levels will continue to rise substantially more over several centuries. On past emissions alone, the world has built up a substantial commitment to sea level rise. One study estimates an existing commitment of between 0.1 and 1.1 metres over 400 years.57

Note the timescale!!! No, we are not being told that sea levels will be 7 metres higher in 2100.

As global temperatures continue to rise, so do the risks of additional sea level contributions from large-scale melting or collapse of ice sheets. If the Greenland and West Antarctic ice sheets began to melt irreversibly, the world would be committed to substantial increases in sea level in the range 5 – 12 m over a timescale of centuries to millennia.65 The immediate effect would be a potential doubling of the rate of sea level rise: 1 - 3 mm per year from Greenland and as high as 5 mm per year from the WAIS.66 For illustration, if these higher rates were reached by the end of this century, the upper range of global sea level rise projections would exceed 1m by 2100.

Centuries to millenia.....note the timescale again. What was happening 1,000 years ago? Should people not have used the horse collar to plough the northern forests of Europe because that would lead to the deforestation of it that we have now?

OK, my verdict (for what such a thing is worth, I'm a blogger after all, not a scientist) is that the timelines all look fine but we'll have a hell of a job reminding everyone that we really are talking centuries to millenia for the sea level rises. Only real compaint is that the issue of climate sensitivty to a doubling of CO2e is overstated which is what gets us some of the scarier predictions.

Chapter 2 here.

October 30, 2006 in Climate Change | Permalink


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"Most climate models" Like the man [Michale Crichton, in 'State of Fear'] said, "models, schmodels"(well, not exactly)where is the hard data? It was warm back in the middle ages (England had good vintages then, apparently) what carbon emissions were resonsible then? Facts is what we want, facts!

Posted by: Marij Sak | Oct 30, 2006 2:03:45 PM

This report's thrown you a bit, hasn't it?

Posted by: Matthew | Oct 30, 2006 10:04:28 PM

As you admitted, you are non-expert. Hence it would help your credibility were you to cite sources in your contradictions of Stern, e.g. the temperature range 2-5 vs 1.5-4.5.

Tim adds: James Annan.

Published peer reviewed papar: although you'll have to search the blog for the description of it. Note that it is climate sensitivity, not temperature change.


Posted by: Jason | Nov 10, 2006 3:01:48 PM