February 16, 2010

Another IPCC Error: Antarctic Sea Ice Increase Underestimated by 50%

Filed under: Antarctic, Climate Changes

Several errors have been recently uncovered in the 4th Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC). These include problems with Himalayan glaciers, African agriculture, Amazon rainforests, Dutch geography, and attribution of damages from extreme weather events. More seem to turn up daily. Most of these errors stem from the IPCC’s reliance on non-peer reviewed sources.

The defenders of the IPCC have contended that most of these errors are minor in significance and are confined to the Working Group II Report (the one on impacts, adaptation and vulnerability) of the IPCC which was put together by representatives from various regional interests and that there was not as much hard science available to call upon as there was in the Working Group I report (“The Physical Science Basis”). The IPCC defenders argue that there have been no (or practically no) problems identified in the Working Group I (WGI) report on the science.

We humbly disagree.

In fact, the WGI report is built upon a process which, as revealed by the Climategate emails, is, by its very nature, designed not to produce an accurate view of the state of climate science, but instead to be an “assessment” of the state of climate science—an assessment largely driven by preconceived ideas of the IPCC design team and promulgated by various elite chapter authors. The end result of this “assessment” is to elevate evidence which supports the preconceived ideas and denigrate (or ignore) ideas that run counter to it.

These practices are clearly laid bare in several recent Petitions to the U.S. Environmental Protection Agency (EPA)—petitions asking the EPA to reconsider its “Endangerment Finding” that anthropogenic greenhouse gases endanger our public health and welfare. The basis of the various petitions is that the process is so flawed that the IPCC cannot be considered a reliable provider of the true state of climate science, something that the EPA heavily relies on the IPCC to be. The most thorough of these petitions contains over 200 pages of descriptions of IPCC problems and it a true eye-opener into how bad things had become.

There is no doubt that the 200+ pages would continue to swell further had the submission deadline not been so tight. New material is being revealed daily.

Just last week, the IPCC’s (and thus EPA’s) primary assertion that “Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic GHG [greenhouse gas] concentrations” was shown to be wrong. This argument isn’t included in the Petition.

This adds yet another problem to the growing list of errors in the IPCC WGI report, this one concerns Antarctic sea ice trends.

While all the press is about the observed declines in Arctic sea ice extent in recent decades, little attention at all is paid to the fact that the sea ice extent in the Antarctic has been on the increase. No doubt the dearth of press coverage stems from the IPCC treatment of this topic.

In the IPCC AR4 the situation is described like this in Chapter 4, “Observations: Changes in Snow, Ice, and Frozen Ground” (p. 351):

As an example, an updated version of the analysis done by Comiso (2003), spanning the period from November 1978 through December 2005, is shown in Figure 4.8. The annual mean ice extent anomalies are shown. There is a significant decreasing trend in arctic sea ice extent of –33 ± 7.4 × 103 km2 yr–1 (equivalent to –2.7 ± 0.6% per decade), whereas the Antarctic results show a small positive trend of 5.6 ± 9.2 × 103 km2 yr–1 (0.47 ± 0.8% per decade), which is not statistically significant. The uncertainties represent the 90% confidence interval around the trend estimate and the percentages are based on the 1978 to 2005 mean.

Notice that the IPCC states that the Antarctic increase in sea ice extent from November 1979-December 2005 is “not statistically significant” which seems to give them good reason to play it down. For instance, in the Chapter 4, Executive Summary (p. 339), the sea ice bullet reads:

Satellite data indicate a continuation of the 2.7 ± 0.6% per decade decline in annual mean arctic sea ice extent since 1978. The decline for summer extent is larger than for winter, with the summer minimum declining at a rate of 7.4 ± 2.4% per decade since 1979. Other data indicate that the summer decline began around 1970. Similar observations in the Antarctic reveal larger interannual variability but no consistent trends.

Which in the AR4 Summary For Policymakers becomes two separate items:

Satellite data since 1978 show that annual average arctic sea ice extent has shrunk by 2.7 [2.1 to 3.3]% per decade, with larger decreases in summer of 7.4 [5.0 to 9.8]% per decade. These values are consistent with those reported in the TAR. {4.4}

and,

Antarctic sea ice extent continues to show interannual variability and localised changes but no statistically significant average trends, consistent with the lack of warming reflected in atmospheric temperatures averaged across the region. {3.2, 4.4}

“Continues to show…no statistically significant average trends”? Continues?

This is what the IPCC Third Assessment Report (TAR), released in 2001, had to say about Antarctic sea ice trends (Chapter 3, p. 125):

Over the period 1979 to 1996, the Antarctic (Cavalieri et al., 1997; Parkinson et al., 1999) shows a weak increase of 1.3 ± 0.2%/decade.

By anyone’s reckoning, that is a statistically significant increase.

In the IPCC TAR Chapter 3 Executive Summary is this bullet point:

…Satellite data indicate that after a possible initial decrease in the mid-1970s, Antarctic sea-ice extent has stayed almost stable or even increased since 1978.

So, the IPCC AR4’s contention that sea ice trends in Antarctica “continues” to show “no statistically significant average trends” contrasts with what it had concluded in the TAR.

Interestingly, the AR4 did not include references to any previous study that showed that Antarctic sea ice trends were increasing in a statistically significant way. The AR4 did not include the TAR references of either Cavalieri et al., 1997, or Parkinson et al., 1999. Nor did the IPCC AR4 include a reference to Zwally et al., 2002, which found that:

The derived 20 year trend in sea ice extent from the monthly deviations is 11.18 ± 4.19 x 103 km2yr-1 or 0.98 ± 0.37% (decade)-1 for the entire Antarctic sea ice cover, which is significantly positive. [emphasis added]

and (also from Zwally et al. 2002),

Also, a recent analysis of Antarctic sea ice trends for 1978–1996 by Watkins and Simmonds [2000] found significant increases in both Antarctic sea ice extent and ice area, similar to the results in this paper. [emphasis added]

Watkins and Simmonds (2000) was also not cited by the AR4.

So just what did the IPCC AR4 authors cite in support of their “assessment” that Antarctic sea ice extent was not increasing in a statistically significant manner? The answer is “an updated version of the analysis done by Comiso (2003).” And just what is “Comiso (2003)”? A book chapter!

Comiso, J.C., 2003: Large scale characteristics and variability of the global sea ice cover. In: Sea Ice - An Introduction to its Physics, Biology, Chemistry, and Geology [Thomas, D. and G.S. Dieckmann (eds.)]. Blackwell Science, Oxford, UK, pp. 112–142.

And the IPCC didn’t actually even use what was in the book chapter, but instead “an updated version” of the “analysis” that was in the book chapter.

And from this “updated” analysis, the IPCC reported that the increase in Antarctic sea ice extent was an insignificant 5.6 ± 9.2 × 103 km2 yr–1 (0.47 ± 0.8% per decade)—a value that was only about one-half of the increase reported in the peer-reviewed literature.

There are a few more things worth considering.

1) Josefino Comiso (the author of the above mentioned book chapter) was a contributing author of the IPCC AR4 Chapter 4, so the coordinating lead authors probably just turned directly to Comiso to provide an unpeer-reviewed update. (how convenient)

and 2) Comiso published a subsequent paper (along with Fumihiko Nishio) in 2008 that added only one additional year to the IPCC analysis (i.e. through 2006 instead of 2005), and once again found a statistically significant increase in Antarctic sea ice extent, with a value very similar to the value reported in the old TAR, that is:

When updated to 2006, the trends in ice extent and area …in the Antarctic remains slight but positive at 0.9 ± 0.2 and 1.7 ± 0.3% per decade.

These trends are, again, by anyone’s reckoning, statistically significant.


Figure 1. Trend in Antarctic ice extent, November 1978 through December 2006 (source: Comiso and Nishio, 2008).

And just in case further evidence is needed, and recent 2009 paper by Turner et al. (on which Comiso was a co-author), concluded that:

Based on a new analysis of passive microwave satellite data, we demonstrate that the annual mean extent of Antarctic sea ice has increased at a statistically significant rate of 0.97% dec-1 since the late 1970s.

This rate of increase is nearly twice as great as the value given in the AR4 (from its non-peer-reviewed source).

So, the peer reviewed literature, both extant at the time of the AR4 as well as published since the release of the AR4, shows that there has been a significant increase in the extent of sea ice around Antarctica since the time of the first satellite observations observed in the late 1970s. And yet the AR4 somehow “assessed” the evidence and determined not only that the increase was only half the rate established in the peer-reviewed literature, but also that it was statistically insignificant as well. And thus, the increase in sea ice in the Antarctic was downplayed in preference to highlighting the observed decline in sea ice in the Arctic.

It is little wonder why, considering that the AR4 found that “Sea ice is projected to shrink in both the Arctic and Antarctic under all SRES scenarios.”

References:

Cavalieri, D. J., P. Gloersen, C. L. Parkinson, J. C. Comiso, and H. J. Zwally, 1997. Observed hemispheric asymmetry in global sea ice changes. Science, 278, 1104–1106.

Cavalieri, D. J., C. L. Parkinson, P. Gloersen, J. C. Comiso, and H. J. Zwally, 1999. Deriving long-term time series of sea ice cover from satellite passivemicrowave multisensor data sets. Journal of Geophysical Research, 104, 15803–15814.

Comiso, J. C., and F. Nishio, 2008. Trends in the sea ice cover using enhanced and compatible AMSR-E, SSM/I, and SMMR data. Journal of Geophysical Research, 113, C02S07, doi:10.1029/2007JC004257.

Parkinson, C. L., D. J. Cavalieri, P. Gloersen, H. J. Zwally, and J. C. Comiso, 1999. Arctic sea ice extents, areas, and trends, 1978– 1996. Journal of Geophysical Research, 104, 20837–20856.

Turner, J., J. C. Comiso, G. J. Marshall, T. A. Lachlan-Cope, T. Bracegirdle, T. Maksym, M. P. Meredith, Z. Wang, and A. Orr, 2009. Non-annular atmospheric circulation change induced by stratospheric ozone depletion and its role in the recent increase of Antarctic sea ice extent. Geophysical Research Letters, 36, L08502, doi:10.1029/2009GL037524.

Watkins, A. B., and I. Simmonds, Current trends in Antarctic sea ice: The 1990s impact on a short climatology, 2000. Journal of Climate, 13, 4441–4451.

Zwally, H.J., J. C. Comiso, C. L. Parkinson, D. J. Cavalieri, and P. Gloersen, 2002. Variability of Antarctic sea ice 1979-1998. Journal of Geophysical Research, 107, C53041.




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