The short answer is that, through September, it certainly is at least among the warmest when we evalute the 2005 tropospheric and ocean heat anomalies. However, it is not yet distinctly the warmest on record with respect to the tropospheric data that is discussed below.
The following headline motivated this weblog. It appeared on October 13, 2005 in a Washington Post article By Juliet Eilperin – “World Temperatures Keep Rising With a Hot 2005”, with the starting text
“New international climate data show that 2005 is on track to be the hottest year on record, continuing a 25-year trend of rising global temperatures.”
This claim is based on the surface air temperature record, which, as we have reported on this weblog (see July 11, 2005 entitled “The Globally-Averaged Surface Temperature Trend- Incompletely Assessed? Is It Even Relevant?”), and will soon have a new posting on this subject, have major problems with using it to assess long-term temperature trends. Moreover, it is not even the most appropriate metric to evaluate global warming (the ocean heat content changes are; see our weblog of September 25, 2005 entitled “Is Global Warming Spatially Complex?”).
Nonetheless, this weblog expands on the Washington Post article and asks the question as to whether the tropospheric temperatures are the warmest on record. We report here on tropospheric temperature trends and the placement of 2005 (through September) with respect to its ranking to earlier years using the information freely available from the Climate Diagnostic Center’s (CDC) website. (As we have stated before, this is an excellent, readily available climate resource). The analysis we present below, of course, should also be compared with other Reanalyses (ERA-40) and satellite assessments (e.g., the UAH and RSS MSU satellite evaluations).
From the CDC web site, we are using the NCEP/NCAR Reanalysis product. We have utilized this Reanalysis for several of our papers in order to assess global and regional tropospheric temperature trends as well as to compare with other analysis products (e.g., Chase, T.N., R.A. Pielke Sr., J.A. Knaff, T.G.F. Kittel, and J.L. Eastman, 2000: A comparison of regional trends in 1979-1997 depth-averaged tropospheric temperatures. Int. J. Climatology, 20, 503-518.) We have developed confidence in its robustness.
In our previous evaluations we concluded that layer-averaged tropospheric temperatures are the more appropriate tool to evaluate trends, rather than the temperature at a single level. We used the Reanalysis data only since 1979 since this is when satellite-derived temperature information became available globally. For the earlier period (back to 1948) it was cooler, as clearly evident in the NCEP/NCAR Reanalysis and as we reported in Pielke et al. (1998a) and Pielke et al. (1998b); but we cannot be certain that this cooler period, at least in part, was not also a result of different available data.
The difference in the heights of two pressure surfaces (referred to as “thickness”) is dependent on the layer-averaged temperature between them, which is calculated from all of the available temperatures between the pressure height levels. The warmer the layer between the two pressure surfaces, the greater the thickness. Since the CDC website does not conveniently provide thickness, however, the discussion below uses pressure altitude as the metric to determine the layer mean temperature between that level and the surface of the Earth. When averaging globally, this does provide a robust measure of the layer-averaged temperature below the selected pressure altitude.
For our analysis below, the rankings of several globally-averaged pressure altitude anomalies are presented for the period since 1979.
For the January-September time period, 2005 was the second warmest (1998 was warmer) for the layer from 300 hPa and 500 hPa to the surface. The 700 hPa layer to the surface was tied with 1998 as the warmest. The 850 hPa layer to the surface tied with 1998 and 2003 (although further back in the record, the early 1950s and late 1940s were appreciably warmer than the more recent years).
At 500 hPa, with respect to the long-term highest globally-averaged pressure heights in the 1980s and 1990s before 1998, the highest pressure altitude in the January-September 2005 was about 0.26% higher. As a reference, the variations of the globally-averaged monthly highest pressure altitudes in the period January to September 2005 varied by about 1%.
The change between the highest globally-averaged 500 hPa pressure altitude in 2005 and the longer-term highest average in the 1980s and 1990s before 1998 corresponds to about a 0.75°C layer-averaged warming. To place this into context, the change during 2005 in the period January to September in the maximum globally-averaged 500 hPa pressure altitude corresponds to about a 3°C variation within this 9 month time period. That is the globally-averaged tropospheric temperatures below 500 hPa within this past year varied by over 4 times what is recorded as the longer-term change.
(The 500 hPa plot was obtained from the NOAA CDC website; the other data for the other pressure altitudes can be extracted from the CDC website in a similar manner).
In terms of long-term trends, there is no significant warming evident in the pressure height at 850 hPa. This contradicts the reported surface warming trend that the Washington Post article reported. At 700 hPa and 500 hPa, there is a warming trend, particularly in the last few years. At 300 hPa, the warming trend is very slight, with only 2005 clearly warmer with respect to the last few years.
This overview of the globally-averaged tropospheric layer-averaged temperatures presents a more complex picture than the simple conclusion reported in the Washington Post. A balanced article would not focus only on the surface data to assess long-term temperature trends.
Moreover, as we have discussed on this weblog (e.g., see “What is the Importance to Climate of Heterogeneous Spatial Trends in Tropospheric Temperatures” ), it is not the globally-averaged surface, nor globally-averaged tropospheric temperature trends that are important in terms of how the weather, and other aspects of the climate system, are affected. It is the regional anomaly pattern.
The CDC website provides this perspective. A plot of the regional anomalies for the January to September 2005 time period with respect to the long-term averages, for instance, can be constructed from http://www.cdc.noaa.gov/cgi-bin/Composites/comp.pl (note that you need to set the time period (January to September), the pressure altitude (check 500 h Pa to relate to the global averaged values referred to earlier in the weblog), and click “anomaly”). This regional assessment shows large areas of both positive and negative temperature anomalies with large areas of January-September 2005 significant cold anomalies. These anomalies clearly are associated with regional weather variations, which are what we should be focusing on in terms of long-term climate trends, rather than surface globally-averaged temperature trends.
This important climate change issue, unfortunately, is consistently ignored in media reports such as the Washington Post despite the subject being highlighted in the 2005 National Research Council report “Radiative forcing of climate change: Expanding the concept and addressing uncertainties.” Committee on Radiative Forcing Effects on Climate Change, Climate Research Committee, Board on Atmospheric Sciences and Climate, Division on Earth and Life Studies, The National Academies Press, Washington, D.C.