In our Editorial of 15 June 2000, we highlighted a number of sources of potential error in surface air temperature measurements and their assemblage into an aggregate history of global climate change. These problems included (1) temporal changes in microclimate surrounding temperature measurement sites, such as urbanization, which often go unrecognized or for which insufficient adjustments are made, (2) long-term degradation of the shelters housing the temperature-measuring equipment, such as the shelters' white paint becoming less reflective and their 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 commonplace in more recent times, (5) general station degradation and many station closures over time, (6) the changing and uneven geographical representation of 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.
Based on our review of these problems, we concluded, as stated in the title of our editorial, that "the global surface air temperature record must be wrong." More specifically, we began to suspect that the highly-hyped "unprecedented" warming of the last two decades of the 20th century may have never occurred. Other observations that support this conclusion include (1) the satellite microwave-sounding-unit temperature record, which in the absence of the massive 1998 El Niņo heat pulse shows no warming whatsoever from 1979 to the present, (2) the weather-balloon temperature record, which for the same circumstances also shows no warming, (3) the surface- and satellite-derived temperature records of earth's polar regions, which also show no warming, and (4) the high-quality U.S. Historical Climatology Network data base, which, not surprisingly, also shows no statistically significant warming over this period.
In our Editorial of 1 July 2000, we continued to pursue this topic, looking at tree-ring-based reconstructions of surface air temperature trends. In the case of an exceptional multiple-tree-ring density-derived reconstruction, which Briffa (2000) calls "the best overall indicator to date of long-term temperature changes over the higher northern land areas," we again found no sign of the supposedly unprecedented late-20th-century warming that forms the basis of so much environmental angst, leading us to conclude, as we stated in the editorial's title, that "there has been no global warming for the past 70 years."
In our Editorial of 15 July 2000, we delved a little deeper into the subject of climate reconstruction based on tree-ring data, noting that there are two types of data that have been used for this purpose: (1) tree-ring width measurements and (2) tree-ring density measurements. Reconstructions based on the first of these parameters often do show what is interpreted as an accelerated warming over the latter part of the 20th century; but reconstructions based on the second parameter do not. The reason for this discrepancy resides in the fact that atmospheric CO2 enrichment significantly enhances biomass production in trees (which results in increased tree-ring widths) by about an order of magnitude more than it enhances wood density. Consequently, the increase in the air's CO2 content over the past century has dramatically increased tree-ring widths, while it has only marginally increased tree-ring densities; and it is this readily-observed CO2-induced increase in tree-ring widths that climate revisionists have wrongly interpreted as being due to an increase in surface air temperature.
We also broached this topic in our Editorial of 2 August 2000, where we reviewed the work of Cowling and Sykes (1999), who independently concluded that "a growing number of physiological and palaeoecological studies indicate that plant-climate interactions are likely not the same through time because of sensitivity to atmospheric CO2." This problem, along with others identified by Darling et al. (2000), suggests that several palaeoclimatic histories may well have to be revised; and the notorious "hockey stick" temperature record of the 20th century stands like an eyesore at the top of the list.
Two other papers we have reviewed in this section of our Subject Index discuss problems associated with reconstructions of past temperature trends based on temperature data obtained from boreholes (Correia and Safanda, 1999) and the significant urban heat island effect of even a small but proximate growing human population (Changnon, 1999). In the first of these studies, the authors identified a number of problems that resulted in erroneous reconstructed temperature trends; while in the latter study, Changnon detected an approximate 0.2°C urban warming bias between 1901 and 1950 in two data sets that had previously been thought to be unaffected by this phenomenon. In commenting on this finding, he noted that "the IPCC (1995) indicated that the global mean temperature increased 0.3°C from 1890 to 1950," implying that a large portion of that temperature rise could well have been due to the undetected influence of concurrently increasing urban-generated heat.
When all is said and done - and what we have discussed here is but the tip of the proverbial iceberg - it is difficult to have much confidence in the IPCC-condoned global temperature history of the past century. There is a very good chance that for the last 70 years of that period there was no net warming at all. If there is anything "unprecedented" about this state of affairs, it is that nearly the whole world has been having an anxiety attack over next to nothing. We can only hope that the climate alarmists' allotted season of being able to "fool all of the people some of the time" will shortly run its course and come to a happy ending, i.e. a reasoned return to reality.
References
Briffa, K.R. 2000. Annual climate variability in the Holocene: Interpreting the message of ancient trees. Quaternary Science Reviews 19: 87-105.
Changnon, S.A. 1999. A rare long record of deep soil temperatures defines temporal temperature changes and an urban heat island. Climatic Change 42: 531-538.
Correia, A. and Safanda, J. 1999. Preliminary ground surface temperature history in mainland Portugal reconstructed from borehole temperature logs. Tectonophysics 306: 269-275.
Cowling, S.A. and Sykes, M.T. 1999. Physiological significance of low atmospheric CO2 for plant-climate interactions. Quaternary Research 52: 237-242.
Darling, K.F., Wade, C.M., Stewart, I.A., Kroon, D., Dingle, R. and Leigh Brown, A.J. 2000. Molecular evidence for genetic mixing of Arctic and Antarctic subpolar populations of planktonic foraminifers. Nature 405: 43-47.
Intergovernmental Panel on Climate Change. 1995. Climate Change 1995. The Science of Climate Change. Cambridge University Press, Cambridge, UK.