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The Global Surface Air Temperature Record May Be Significantly in Error
Volume 3, Number 12: 15 June 2000

Although we rarely deal with things not published in the conventional peer-reviewed scientific literature, we take exception this issue to discuss a matter that has recently been addressed in several such publications.  This deviation from our standard policy is taken for the important reason that these publications have convinced us that the global surface air temperature record, which is used to support the idea that the earth has warmed dramatically over the past century or so, may be incorrect.

Our tentative conversion on this matter began with our reading of John Daly's treatise on the global surface air temperature record (Daly, 2000), which is posted on the website of the Greening Earth Society (  In reference to the divergent trends of the surface air temperature record, which exhibits a dramatic warming over the past 21 years, and the lower tropospheric temperature record produced by satellite microwave sounding units, which exhibits no such warming, he cites the only three explanations that can possibly account for this discrepancy: (1) the surface record is incorrect, (2) the satellite record is incorrect, (3) both records are correct, and their different temperature trends are due to some unknown atmospheric process or processes.

Considering the same issue, Balling (2000) notes that the recent National Research Council (2000) report on the subject acknowledges that the two records should produce similar trends: "if global warming is caused by the buildup of greenhouse gases in the atmosphere, it should be evident not only at the earth's surface, but also in the lower to mid-troposphere."  Indeed, the report says that the best climate models available "predict that the lower to mid troposphere should warm at least as rapidly as the earth's surface."  Hence, since the two temperature trends should be close to identical, Daly's third explanation for their divergence can be ruled out, leaving us either his first or second explanation as the correct one.

Daly opts for explanation number one - the surface air temperature record is incorrect.  He supports his contention with illustrations of a number of potential sources of error that are known to plague this record: (1) temporal changes in microclimate surrounding the temperature measurement site, such as urbanization, which go unrecognized or for which insufficient adjustments are made, (2) long-term degradation of the shelter housing the temperature-measuring equipment, such as its white paint becoming less reflective and its louvers partially obstructed, (3) changes in what is actually being measured, such as true daily maximum and minimum temperatures or temperatures at specified times of day, (4) changes in measurement devices and ways of accessing the data, such as changing from having to open the shelter door to read the temperature, as was done in earlier days, to not having to do so due to the automatic recording of the data, as has become typical in more recent times, (5) general station degradation and many station closures over time, (6) changing and uneven geographical representation in the surface temperature network, (7) poor attention to careful acquisition of data in many parts of the world, and (8) a number of problems associated with obtaining a correct and geographically complete record of surface air temperature over the 70% of the globe that is covered by oceans.

Michaels and Balling (2000) additionally point out the great difficulty of appropriately correcting for the onset and development of urbanization effects in stations that once were considered rural but have, in the past decade or two, experienced the encroachment of nearby cities.  As they describe the situation, urban effects have largely been removed from specific temperature records when they dominate them for many decades; but when encroaching urbanization has begun to exert its influence over only the past 10 to 15 years, "we have no objective mechanism for isolating the effect." Hence, as they correctly state, "the urban effect is here [in the latter part of the record], and it will grow exponentially."

But how do we absolutely know that all, or even any, of these potential problems are indeed occurring?  One way suggested by Balling is to compare the satellite record with the surface air temperature record over the portion of the earth that is known to possess the highest quality surface air temperature data.  This data set comes from the U.S. Historical Climatology Network, and contains, among other things, monthly averages of mean near-surface air temperature for 1,221 high-quality largely non-urban stations within the 48 contiguous states of the United States of America.

In making this comparison, Balling found that the surface and satellite records for this portion of the globe were nearly identical, and that each showed no statistically significant trend, nor did the time series of differences between them show any such trend.  He acknowledges, however, that the conterminous United States only covers 1.54% of the earth's total surface area; but he makes the point that the best near-surface air temperature records to be found on the planet match up beautifully with the measurements made from satellites.  We thus conclude with him that if equally good surface air temperature records were available for the rest of the earth, they too would match up equally beautifully with the corresponding satellite record ... and show very little warming.

But are there any other reasons to believe that this should be the case?  In a word, yes.  And we start with a contribution from Daly on this point.

Daly notes that although various climate models differ substantially in their predictions of greenhouse warming around the globe, they all agree on one thing: the warming, if it occurs at all, should be accentuated in earth's higher latitudes.  Hence, the planet's polar regions should be prime candidates for displaying the postulated warming.  But when high-quality scientifically-supervised temperature records from these regions of the earth - both north and south - are checked, they too show very little warming.

Finally, we have the radiosonde or weather balloon record of temperature in the same part of the atmosphere that is monitored by satellite.  Both Balling and Daly point out that its temperature history of the past two decades closely mirrors that of the satellite record, and that it once again shows very little if any warming.

In view of the near-perfect agreement among the satellite and surface records over the conterminous United States, which all show little warming over the past two decades, as well as the similar finding of little warming in high-quality stations from both of the earth's polar regions, where greenhouse warming is predicted to be greatest, plus the fact that the satellite and balloon records show little to no warming over the entire earth over this period, we thus conclude that there truly has been little if any warming due to any cause over this period of time over the entire planet, and that the only reason the surface record for the globe shows warming is that outside of the United States and a few other places of high-quality temperature measurement, the surface record is just plain wrong, for the host of reasons listed, described and illustrated by Daly, Balling, and Michaels.  Furthermore, since the significant increase in greenhouse gas radiative forcing experienced to date should have produced a sizeable warming by now, if it were not thwarted by compensating mechanisms in the real atmosphere, we also believe there is no compelling reason to believe that it will necessarily produce much warming in the foreseeable future.

Dr. Craig D. Idso
Dr. Keith E. Idso
Vice President

Balling Jr., R.C.  2000.  Reconsidering reconciliation: Understanding the NRC report.  In: Michaels, P.J. (Ed.).  State of the Climate Report: Essays on Global Climate Change.  New Hope Environmental Services, pp. 8-13.

Daly, J.L.  2000.  The surface record: "Global mean temperature" and how it is determined at surface level.  Report to the Greening Earth Society.  Available at

Mann, M.E., Bradley, R.S. and Hughes, M.K.  1999.  Northern Hemisphere temperatures during the past millennium: Inferences, uncertainties, and limitations.  Geophysical Research Letters 26: 759-762.

Michaels, P.J. and Balling Jr., R.C.  2000.  The Satanic Gases: Clearing the Air About Global Warming.  Cato Institute, Washington, DC.

National Research Council, Panel on Reconciling Temperature Observations.  2000.  Reconciling Observations of Global Temperature Change.  National Academy Press, Washington, DC.