Monday, February 05, 2007

The 59cm myth (with an appearance of ‘the global warming has ended’ myth)

As expected, the release of Climate Change 2007: The physical Science Basis (Summary for policymakers) has caused a new front to open in the battle between the forces of good and the forces of denialism. There has been a concerted attempt by a number of contrarians with media access to use the findings of the summary to discredit claims about the degree of climate change and its impacts.

A lot of these claims seem to revolve around the myth that the IPCC summary states that sea-levels will raise by a maximum of 59cm by 2099.

One such article, by Jennifer Marohasy of the free-market think-tank The Institute of Public Affairs, is published in today’s Courier Mail. It is entitled “How much hot air?”, and makes the following claim:
For example, while Al Gore claimed that sea levels are about to rise by more than 6m, the IPCC summary indicates that sea levels have risen by just 17cm and may rise by no more than another 18cm, certainly no more than 59cm by 2099.

Did Al Gore claim that sea-levels are certain to rise by slightly more than 6m by 2099? Jen’s statement about Gore’s claim is fairly unequivocal; this is not something that may happen, but something that will happen. But I’m not sure if that was the exact claim he made (I’m happy to be proven wrong. Was there certainty in Gore’s claims and was it definitely going to happen before 2100?). If my memory serves me correctly he claimed that if there was significant melting of the polar caps and Greenland, this magnitude of rise in sea level was possible.

So what does the IPCC summary say?
Global average sea level in the last interglacial period (about 125,000 years ago) was likely 4 to 6 m higher than during the 20th century, mainly due to the retreat of polar ice. Ice core data indicate that average polar temperatures at that time were 3 to 5°C higher than present, because of differences in the Earth’s orbit.
Knowing that the sea levels were this high in the past in a similarly warmer world to what is expected in the future shows that Gore’s claim isn’t as silly as it first sounds. It remains in the realm of possibility that sea-levels may rise by 20ft, though it’s extremely unlikely to happen in the next 100 years.

Again, I’d be interested if someone could fill me in on the EXACT nature of Gore’s claim and if certain embellishments haven't been added in the re-telling.

But it’s actually the final numbers in the editorial paragraph that are particularly revealing.
.....the IPCC summary indicates that sea levels have risen by just 17cm and may rise by no more than another 18cm, certainly no more than 59cm by 2099.
Why are they revealing? Because the IPCC summary shows that this statement is critically wrong for two reasons.

1. There are a number of scenarios given and the sea-level response for each. The most pessimistic scenario gives a sea-level rise of 59cm, with the explicit caveat that this figure does not include future rapid dynamical changes in ice flow. Directly below this is stated:
The projections include a contribution due to increased ice flow from Greenland and Antarctica at the rates observed for 1993-2003, but these flow rates could increase or decrease in the future. For example, if this contribution were to grow linearly with global average temperature change, the upper ranges of sea level rise for SRES scenarios shown in Table SPM-2 would increase by 0.1 m to 0.2 m. Larger values cannot be excluded, but understanding of these effects is too limited to assess their likelihood or provide a best estimate or an upper bound for sea level rise.
As is evident if you bother to read this note, 59cm plus 20cm (79 cm in total) is the likely upper limit to sea-level rise by 2100 though, due to a lack of understanding of likely ice flow rates, an even greater rise cannot be ruled out. This leads me to the second error:

2. Nowhere in the summary is absolutely certainty expressed about anything, let alone sea-level rises. Some things are virtually certain, such as increased temperature in the future. The summary explicitly states that there are uncertainties associated with the upper levels of these sea-level rise predictions.

You’d think that if you going to write an editorial in a major Australian newspaper about how global warming realists are getting their facts wrong, you’d actually get yours right.

Not in this case. Not by a long stretch.

When informed on her blog that there were errors in her article Jen replied:
Nexus, I appreciate your point, I could have been more careful with my words.
Actually, she should have just admitted that she was wrong. Being incorrect in this case is not simply a matter of maybe being not careful enough with words. The statement in the editorial was flat out wrong; that’s all there is to it. It shouldn’t be that hard to admit that this is the case. I’ve even provided an example of how to go about admitting one’s errors when they are pointed out:
And so could you [be more careful with your words]... I suggest we refer to the document as the IPCC SUMMARY of the IPCC report due out in May. You keep referring to it incorrectly as 'the report'.
To which I immediately replied:
Good point, Jen. I stand corrected. Summary for policymakers it is.
See kiddies, it’s not that hard!

So, were there more errors in the editorial? You bet ya, a big one!
But the IPCC summary glosses over various anomalies. For example, while the global trend has been one of warming, a plot of mean temperatures since 1998 shows that there has been no warming since then, now eight years later.

The IPCC summary does not acknowledge the current downward trend, which may or may not prove to be just a blip in the scheme of things.
No warming since 1998? A downward trend?! WTF!

Let us conduct this experiment of plotting mean temperatures since 1998 and see if there has been no warming since then, and if a downward trend is evident. To do this I have used the NASA GISTEMP data set for Global Annual Mean Surface Air Temperature Change, which can be found here. There are no adjustments to data such as smoothing. Temperature changes from 1980 are plotted to show if there is any marked change in the trend since 1998.

You judge for yourself. Has warming stopped since 1998? Is there a downward trend in temperature since 1998? There are certainly some ups and downs associated with ENSO, but an upward trend since 1998 is clear. The reality of global warming, as opposed to the myths in the editorial, could not be more stark.

EDIT: Typo fixed. Sorry Eli.