Do The CRU E-mails Change The IPCC Conclusions On The late 19 th , 20th and early 21st Century Surface Temperature Trends?

Does The CRU Data (and thus the IPCC) Overstate The Magnitude Of Global Warming?

The answer to the first question is NO.

The answer to the second question is YES.

There has been a lot of speculation that the exposure of the inappropriate handling of the surface temperature data at CRU means that the IPCC conclusion of the late 19th, 20th , and early 21st century surface temperature trends will be changed. Also, that the missing instrumental data means that the raw data from which these trends were reported is lost.

However, neither of these conclusions are true. The other centers (GISS; NCDC, and presumably the Japanese analysis) draw from essentially the same set of raw data. This was reported in the report CCSP 1.1, where it is written on page 51

“While there are fundamental differences in the methodology used to create the surface data sets, the differing techniques with the same data produce almost the same results (Vose et al., 2005a). The small differences in deductions about climate change derived from the surface data sets are likely to be due mostly to differences in construction methodology and global averaging procedures.”

Thus, since these other data analyses remain, the IPCC conclusion on the long-term trends will be unchanged (see also).

However, there are fundamental remaining issues with all of these surface temperature analyses, as we reported in detail in

Pielke Sr., R.A., C. Davey, D. Niyogi, S. Fall, J. Steinweg-Woods, K. Hubbard, X. Lin, M. Cai, Y.-K. Lim, H. Li, J. Nielsen-Gammon, K. Gallo, R. Hale, R. Mahmood, S. Foster, R.T. McNider, and P. Blanken, 2007: Unresolved issues with the assessment of multi-decadal global land surface temperature trends. J. Geophys. Res., 112, D24S08, doi:10.1029/2006JD008229,

which have not been adequately addressed by any of these analysis centers. These include the lack of quantitative assessment of the statistical uncertainty associated with the time of observation bias and change of instrumentation, and of the degree of dependence imposed when “homogenizing” nearby observing sites. There are also systematic (i.e. non-random) effects introduced into the surface air temperature from non-climatic site exposures (e.g. see).

I understand that the CRU analyses are going to be redone from the raw data (e.g. see). If this is correct, and I hope it is, than each step for every site must be clearly documented and traceable. Photographs of the quality of each location must be a requirement (with all historical photographs sought out also). It is only with this information that a truly open scientific assessment can be achieved.

There is also the issue of attribution of actual climate forcings with respect to reported surface temperature trends. The diagnosis of an average land surface temperature anomaly is motivated by the IPCC focus on the global average surface temperature trend as the primary metric to assess the global average radiative forcing. However, there are other effects besides changes in radiative forcing that can alter the long-term surface temperature, of which land use change, concurrent trends in surface air water vapor content, and aerosols have been shown exert a major influences. For example, see

Fall, S., D. Niyogi, A. Gluhovsky, R. A. Pielke Sr., E. Kalnay, and G. Rochon, 2009: Impacts of land use land cover on temperature trends over the continental United States: Assessment using the North American Regional Reanalysis. Int. J. Climatol., DOI: 10.1002/joc.1996.

where we documented that systematic increases in surface air temperature resulted in the USA for most landscape conversions,

Fall, S., N. Diffenbaugh, D. Niyogi, R.A. Pielke Sr., and G. Rochon, 2009: Temperature and equivalent temperature over the United States (1979 – 2005). Int. J. Climatol., submitted.

where we document effects on surface air temperature due to concurrent trends in water vapor content,

and

Yan Huang, Robert E. Dickinson, and William L. Chameides, 2006: Impact of aerosol indirect effect on surface temperature over East Asia. PNAS 2006 103:4371-4376; published online before print March 14, 2006, doi:10.1073/pnas.0504428103

where they write in their abstract

“A regional coupled climate–chemistry–aerosol model is developed to examine the impacts of anthropogenic aerosols on surface temperature and precipitation over East Asia. Besides their direct and indirect reduction of short-wave solar radiation, the increased cloudiness and cloud liquid water generate a substantial downward positive long-wave surface forcing; consequently, nighttime temperature in winter increases by +0.7°C, and the diurnal temperature range decreases by −0.7°C averaged over the industrialized parts of China. Confidence in the simulated results is limited by uncertainties in model cloud physics. However, they are broadly consistent with the observed diurnal temperature range decrease as reported in China, suggesting that changes in downward long-wave radiation at the surface are important in understanding temperature changes from aerosols. “

These studies, and that of other climate scientists, indicate that the use of the surface temperature trends (from CRU, GISS and NCDC) as a diagnostic for heating changes for the entire climate system (i.e. global warming) will overstate the actual change that can be attributed to the radiative effect due to the increase of the well mixed greenhouse gases, since part of the increase in surface air temperature in the late 19th, 20th and early 21st century is due to land use change, concurrent water vapor trends, and atmospheric aerosols.

Our new paper

Klotzbach, P.J., R.A. Pielke Sr., R.A. Pielke Jr., J.R. Christy, and R.T. McNider, 2009: An alternative explanation for differential temperature trends at the surface and in the lower troposphere. J. Geophys. Res., 114, D21102, doi:10.1029/2009JD011841 (see for corrigendum)

documents the magnitude of the warm bias by examining the divergence in trends over time between the surface air and lower tropospheric temperature trends. Our latest estimate of the bias is presented in Table 2 of

Klotzbach, P.J., R.A. Pielke Sr., R.A. Pielke Jr., J.R. Christy, and R.T. McNider, 2009: Corrigendum to: “An alternative explanation for differential temperature trends at the surface and in the lower troposphere. J. Geophys. Res., 114, D21102, doi:10.1029/2009JD011841″, J. Geophys. Res., submitted.

This bias means that the magnitude of the positive global average surface temperature trend since at least 1979 that was reported in the 2007 IPCC report as well as the global average surface temperature anomalies reported yesterday by the WMO at the Copenhagen meeting (e.g. see) are too large.