Re: Global warming: It's happening
by Kevin E. Trenberth
From: S. Fred Singer
Date: Thu, 29 Jan 1998 09:51:28 -0500
Subject: Comments on Trenberth's article of December 4
Global warming is not happening
Dr. Kevin Trenberth ("Global Warming: Itís Happening," naturalSCIENCE, December 4, 1997) has severely criticized a feature article in the (Toronto) Globe and Mail newspaper (November 22, 1997). He is wrong on many counts.
Trenberth informs us that "climate is changing." No problem there. Mean temperatures rose steeply in the decades before 1940 and dropped from 1940 to about 1975. Most climatologists agree that these changes were of natural origin--although Trenberth tries to present them as of human origin. But then he claims that "global mean temperature is rising." Not so. The weather satellite data, the only truly global data set we have, actually show a global cooling trend during the past 19 years.
Trenberth then cites his critique of these satellite results. Thatís all good and proper, and part of the ongoing scientific debate about global warming. But he should have informed the reader of the able response by John Christy and Roy Spencer, who are responsible for the analysis of these data. And he should have also mentioned that balloon-borne weather sondes provide an independent set of data that confirm the satellite results of ongoing global cooling.
In fact, it is the surface data that are suspect, and especially the data that purport to measure the temperature of the sea surface. The oceans cover 70 percent of the Earth, but only a small fraction is actually observed. At least four different techniques are somehow combined to give a "global" value, with grave doubts about the intercalibration. As the mix of data sources changes over time, it is likely to introduce a temperature trend that is largely an artifact.
Trenberth is out of his specialty when he describes some of the imagined consequences of a global warming, such as floods and droughts. Along with Vice President Al Gore, he cites the 1997 North Dakota flood as an example. Trenberth should find himself a better expert, like Harry Lins of the US Geological Survey, who has actually analyzed flood data and reports no increasing trend (Am. Geophys. Union Meeting, December 1997).
Trenberth bemoans the "politicization of science"--and so do we. He refers the reader to the George Brown article in the March 1997 issue of Environment, which is based on a blatantly partisan staff report. The reader is not told about the replies to Brown in the May issue that sets the record straight.
Finally, Trenberth drags out the hoary consensus of "over 2000 IPCC scientists." I have analyzed this fabricated claim in some detail (see Wall Street Journal, July 25, 1997). There are, at best, only about 100 climate scientists in this IPCC listing of economists, political scientists, government functionaries, and public relations specialists. Not that numbers matter, but among the 100 bona-fide experts there are many who disagree with the "consensus"--as determined by several independent polls. (See also the May 16, 1997 issue of Science.) And there are even some who have publicly expressed their disagreement by signing the "Leipzig Declaration"--which now numbers over 100 signers.
From: Kevin E. Trenberth
Reply to Fred Singer
The process of science is one where hypotheses are formed and revised in the light of new information. The quality of information is a key and Singer is guilty of very selective use of the information available.
Global temperatures fluctuate on various time scales even in the absence of any climate change. For instance, a typical El Niño is responsible for rises in global mean temperatures of a tenth degree Celsius, and a major El Niño, such as we have had in 1997, contributes even more. It has now emerged that 1997 is the warmest year on record in the surface temperatures. So it is always possible to select a point, such as 1940, and say there has been a decline in temperatures for a while since then. It so happens that 1939 to 1942 was one of the biggest and longest duration El Niño events on record. Unfortunately it is not as well documented as recent events so its true magnitude is hard to determine. To claim that temperatures declined from 1940 to 1975, as Singer does, is disingenuous. Examining the entire record, as given in the figure in my article, shows the underlying strong slow upward trend, as expected with global warming.
Singer cites the satellite record as showing a downward trend (since 1979 when it began). The satellite record is made up of contributions from nine different satellites and it does not measure surface temperatures but instead measures temperatures through a broad layer of the atmosphere. Moreover, there are two satellite records of the troposphere (the lower atmosphere from the surface to about 35,000 feet altitude). The one cited by Singer shows a downward trend whereas the other shows an upward trend. Furthermore, the latter record is demonstrated to be much more reliable (by a factor of three or more) by comparisons between satellites when more than one is flying at the same time. The downward trend has been clearly shown to be spurious (Hurrell and Trenberth 1997, 1998). The record referred to by Singer is manipulated to represent a layer closer to the surface (surface to 25,000 feet or so) but at the expense of contamination from ground effects. The same balloon-borne measurements used by Christy et al. (1997) clearly and unequivocally show that in some places, such as over Australia, the satellite record is wrong (see the reply by Trenberth and Hurrell, and Hurrell and Trenberth 1998), because of flaws in how the records of different satellites were joined up.
Singer is incorrect when he refers to areas of my specialty as I have published extensively on the hydrological cycle (but not in the Wall Street Journal). It is a fact that much of the global heating from increased greenhouse gases goes into evaporating moisture. This process keeps the planet Earth cooler and more moderate than if no water were present. The greatest heat waves occur during droughts when water is in short supply. The resulting increased atmospheric moisture then feeds all precipitating weather systems and increases snow and rainfall amounts. Those increases too are observed to be happening. It is harder to document changes in floods because of extensive changes in how water flows through culverts and across surfaces, because of dams, reservoirs, levees, and other human changes.
As to the correspondence in the Environment following Congressman George Brown's article, Singer fails to mention the rebuttal by Brown and other correspondence there in support of Brown that did help set the record straight. Unlike Singer's rhetoric, the IPCC statements were based on careful evaluation of all the evidence and represent a true consensus. It does not mean that everyone agrees with the exact wording but they do agree with the meaning and intent. It is well known that a simple change in wording of a poll can greatly change the outcome.