Open Mind

The Thermometer Record

November 21, 2006 · 2 Comments

Temperature records from thermometer measurements have been maintained over large areas of the globe for a century and a half, and in a few locations for several centuries. Numerous researchers have collected and organized these measurements, checking them carefully so that errors can be corrected if possible and eliminated if not, and compensating for all known biases and nonclimatological factors. The world’s two leading scientific institutions maintaining accurate and consistent temperature records are the Hadley Centre for Climate Research in the U.K. (HadCRU) and NASA’s Goddard Institute for Space Studies (GISS) in the U.S. They further estimate global and hemispheric averages of temperature; these data are the source for most of the temperature graphs published in the mass media.

Urban “heat-island” effects (UHI)

Lord Monckton, in his argument against the reality of global warming, goes to great lengths to cast doubt on the temperature record. He first suggests Urban “heat-island” effects. It is a well-known meteorological phenomenon that urban areas tend to be warmer than rural, especially at night; this is the urban heat island, or UHI effect. This is corrected for, but Monckton suggests on pg. 16 that, “it is possible that insufficient allowance has been made.”

To look for UHI contamination in temperature records, Peterson et al. (1999) took the available temperature data and created two sets for comparison. One was the whole set of data, the other was produced using only the rural stations. The trend from 1880 to 1998 was 0.7 oC per century for just the rural stations; including the urban data did not artificially inflate the warming estimate, but rather deflated it to 0.65 oC per century. Similarly, Parker (2004) sought differences caused by UHI, by comparing temperature trends for windy days and calm days; windy conditions are known to reduce the UHI. Parker found:

This analysis demonstrates that urban warming has not introduced significant biases into estimates of recent global warming. The reality and magnitude of global-scale warming is supported by the near-equality of temperature trends on windy nights with trends based on all data.

In the most comprehensive survey to date, Peterson (2003) studied the relationship of temperature records to urbanization, as well as to a numerous other factors including elevation, latitude, time of observation, instrumentation, and nonstandard siting. His finding was:

Contrary to generally accepted wisdom, no statistically significant impact of urbanization could be found in annual temperatures. It is postulated that this is due to micro- and local-scale impacts dominating over the mesoscale urban heat island. Industrial sections of towns may well be significantly warmer than rural sites, but urban meteorological observations are more likely to be made within park cool islands than industrial regions.

The effect of urbanization has been studied in detail and is compensated for effectively. The Urban Heat Island effect is no longer tenable as a reason to doubt the temperature trend indicated by the thermometer record.

Incomplete historical record

Monckton goes on to argue that we have an Incomplete historical record, saying:

The only reliable records for the first half of the 20th century are from the US. In the UK and other European centres, the ratio of population to land area is too great to allow accurate comparisons; in most other areas, political instability prevents a complete record. Many historically-inaccurate or poorly-correlated records have been used in all reconstructions of 20th-century temperature.

Contrary to his claims, reliable records cover large areas of the globe for the entire 20th century, and coverage of the northern hemisphere is especially good. Interruptions in individual records don’t prevent us from reconstructing hemispheric and global averages that can be relied upon. Nor does the “ratio of population to land area” invalidate accurate comparisons; this is simply the urbanization argument again.

Antarctica/Greenland/Iceland

One of the subjects Monckton treats at length is The Antarctic and Greenland/Iceland temperature anomalies. Regarding Antarctica, on pg. 18 he refers to, “See Sansom (1989) for the Antarctic temperature series,” but Sansom studies only 30 years of temperature data (from 1957 to 1987) and finds no statistically signficant trend. On pg. 19 Lord Monckton states, “In Iceland, as in Greenland, the first half of the 20th century was warmer than the second half.”

The whole argument is predicated on the assumption that “global warming theory” requires warming to be uniform. In fact Monckton concludes on pg. 19, “I conclude that the rise in temperatures since 1900 has been far from uniform globally.” However, modern climate science does not predict uniform warming at all; it predicts that regional differences are expected, not contradictory. Even if Monckton’s characterization of temperature trends in Antarctica, Greenland, and Iceland were true, these regions are not the world.

Antarctica is an isolated continent sitting on top of the south pole. As such it’s expected to respond differently to global warming than other areas of the globe. The Antarctic peninsula is warming rapidly, as evidenced by thermometer records and by the recent collapse of the Larsen B ice shelf. Interior stations show a very small cooling over the last 20 years but no discernable trend over the 20th century. As for Iceland, its temperature since 1900 from stations reporting to the global historical climate network (ghcn) belies the claim that “the first half of the 20th century was warmer than the second half.”

iceland_ghcn.JPG

References:

Parker, D.E. 2004, Large-scale warming is not urban, Nature 432, 290

Peterson, T.C., K. P. Gallo, J. Lawrimore, T. W. Owen, A. Huang, and D. A. McKittrick, 1999: Global rural temperature trends. Geophysical Research Letters 26, 329

Peterson, T.C. 2003, Assessment of Urban Versus Rural In Situ Surface Temperatures in the Contiguous United States: No Difference Found, Journal of Climate 16, 2941

Sansom, J. 1898, Antarctic Surface Temperature Time Series, Journal of Climate 2, 1164

US DOE 2006, web site of the U.S. Department of Energy, http://www.eia.doe.gov/kids/infocardnew.html

Categories: Global Warming

2 responses so far ↓

  • EW // June 8, 2007 at 1:28 pm

    What happened to Iceland in the 1930’s? Since then, apart from cold 70’s nothing changed.

    [Response: The temperature history of Iceland is discussed in more detail in the next post.]

  • chrisl // June 13, 2007 at 9:15 am

    Peterson states that ” urban meteorological observations are more likely to be made within park cool islands than industrial regions.”
    How does this square with airports that may have started out rural, on to propellor planes,now jets, and have turned into 24 hr megacities.
    You would have to concede there would be an amount of UHI there.

  • Like gas stations in rural Texas after 10 pm, comments are closed.