In even an overview of the section in the 2007 IPCC Statement For Policymakers on “Direct Observations of Recent Climate Change” there are errors, or at best selective information, in their findings. I am summarizing four on this weblog:
1. The IPCC SPM writes on page 7
“… snow cover have declined on average in both hemispheres.”
The Rutgers University Global Snow Lab Northern Hemisphere Snow Cover Anomalies plot through January 2007, however, shows that the areal coverage in the Northern Hemisphere has actually slightly increased since the later 1980s!
Since the inference from the IPCC SPM is that global warming is the reason for these changes, this is at best a clear example of selecting a time period that conforms to their conclusion rather than presenting an up-to-date description of snow cover trends.
2. The IPCC SPM writes on page 7
“Observations since 1961 show that the average temperature of the global ocean has increased to depths of at least 3000 m and that the ocean has been absorbing more than 80% of the heat added to the climate system.”
It is correct that the ocean is where most of the heat changes occur, but the finding conveniently neglected to report on the significant loss of heat in the period from 2003 to at least 2005;
Lyman, J. M., J. K. Willis, and G. C. Johnson (2006), Recent cooling of the upper ocean, Geophys. Res. Lett., 33, L18604, doi:10.1029/2006GL027033.
As stated in that paper,
“The decrease represents a substantial loss of heat over a 2-year period, amounting to about one fifth of the long-term upper-ocean heat gain between 1955 and 2003 reported by Levitus et al. .”
In addition, even with the earlier ocean warming, this is what was found in the paper
Willis, J. K., D. Roemmich, and B. Cornuelle (2004), Interannual variability in upper ocean heat content, temperature, and thermosteric expansion on global scales, J. Geophys. Res., 109, C12036, doi:10.1029/2003JC002260.
â? Maps of yearly heat content anomaly show patterns of warming commensurate with ENSO variability in the tropics, but also show that a large part of the trend in global, oceanic heat content is caused by regional warming at midlatitudes in the Southern Hemisphere. â?
They report that,
ââ¦â¦a strong, fairly linear warming trend is visible in the Southern Hemisphere, centered on 40Â°S. This region accounts for a large portion of the warming in the global average.â?
ââ¦â¦..the warming around 40Â°S appears to be much steadier over the course of the time series, as seen in Figure 7. In addition, this warming extends deeper and is more uniform over the water column than the signal in the tropics. â?
Thus the actual global ocean warming reported in the IPCC SPM over the last several decades occured in just a relatively limited portion of the oceans and through depth such that the heat was not as readily avaiable to the atmosphere as it would be if the warming was more spatially uniform.
Moreover, if the ocean has been absorbing “more than 80% of the heat added to the climate system”, why does the SPM use the surface air temperature trends to define what is a warm year? The IPCC SPM makes such a claim on page 5, where it is written that
“Eleven of the last twelve years (1995 -2006) rank among the 12 warmest years in the instrumental record of global surface temperature (since 1850).”
If the ocean absorbs most of the heat (which Climate Science agrees with), than that is the climate metric that should be reported on with respect to global warming, rather than the global average surface temperature trend data.
3. The IPCC SPM writes on page 7,
“The average atmospheric water vapour content has increased since at least the 1980s over land and ocean as well as in the upper troposphere. The increase is broadly consistent with the extra water vapour that warmer air can hold.”
This conclusion conflicts with the finding in
Smith, T. M., X. Yin, and A. Gruber (2006), Variations in annual global precipitation (1979â2004), based on the Global Precipitation Climatology Project 2.5Â° analysis, Geophys. Res. Lett., 33, L06705, doi:10.1029/2005GL025393,
where they write for the period 1979â2004 that precipitation tends
“have spatial variations with both positive and negative values, with a global-average near zero.”
The global average precipitation has not changed significantly in the period.
If greater amounts of water vapor were present in the atmosphere, the evaporation/transpiration of water vapor into the atmosphere and thus the precipitation would have to increase when averaged globally and over a long enough time period.
4. The IPCC SPM writes,
“Mid-latitude westerly winds have strengthened in both hemispheres since the 1960s.”
This is perhaps the most astonishing claim made in the report. First, peer reviewed papers that have investigated this subject,
Pielke, R.A. Sr., T.N. Chase, T.G.F. Kittel, J. Knaff, and J. Eastman, 2001: Analysis of 200 mbar zonal wind for the period 1958-1997. J. Geophys. Res., 106, D21, 27287-27290.
did find a
“….tendency for the 200 mbar winds to become somewhat stronger at higher latitudes since 1958.â?
However, what this means from basic meteorology, is that if the mid-latitude westerlies increase, this indicates a greater north-south tropospheric temperature gradient! This is why the westerlies are stronger in the winter; the troposphere becomes very cold at the higher latitudes, but the tropospheric temperatures change little in the tropics. Thus a statement that the westerlies have become stronger, in the absence of significant warming in the tropical latitudes, indicates a colder troposphere at higher latitude on average.
There is, therefore, an inconsistency in the IPCC SPM. It cannot both be the case that the troposphere in the arctic is warming high while the westerlies in the midlatitudes are increasing in speed. There is a fundamental inconsistency in these trends, which goes unaddressed by the IPCC.
These four examples illustrate the apparent selection of papers and data to promote a particular conclusion on climate change. The science community, and even more importantly, the policy community is ill-served by such cherry picking.