"New Evidence Helps Reconcile Global Warming Discrepancies; Confirms That Earth's Surface Temperature Is Rising" describes how surface temperatures have warmed in the past 20 years, even though upper-atmosphere temperatures have remained stable. This "surface warming" is said to be due to "a combination of human activities and natural causes," and is reputed to be real evidence that the earth's temperature is rising.
While I agree with most of what appears in the press release, some additional comments are warranted. As a state climatologist, one whose job it is to examine data records for quality, I am very cautious about using data from individual stations to infer global trends. Local biases, particularly the "urban heat island" effect, can bias temperature measurements. Tom Karl, Director of the National Climatic Data Center (NCDC), has the same concerns. For that reason, Karl initiated the Historical Climatology Network (HCN) program a number of years ago. NCDC selected reliable long-term stations, those thought to be free of local biases (neglecting, for example, stations in growing urban areas). When HCN temperature trends are plotted for the last 105 years, there is a very slight warming, but the warmest period of the century occurred in the late 1930s and early 1940s. See for yourself: http://www.ncdc.noaa.gov/ol/documentlibrary/cvb.html. The December issues of Climate Variations Bulletin show the annual trends.
What this means is that the long-term trends in temperature in one of the largest countries in the world, using the finest available surface temperature data, do not show the warming that the global data sets indicate. Why not? As Tom Karl suggested in the March, 1989 Bulletin of the American Meteorological Society, "all global temperature data sets are contaminated by a number of biases of varying magnitudesof which the most serious may be the global-warming bias." These statements, which were Karl's rationale for formulating the HCN, still ring true. My explanation for the difference between U.S. temperatures (which show almost no warming this century) and global data (which show a lot) is that the latter is of considerably lower quality, and much more biased, than the carefully-constructed HCN data set.
One of the best overviews on global climate changed I have seen was Pat Michaels' testimony before the Subcommittee on National Economic Growth, Natural Resources and Regulatory Affairs, of the U.S. House of Representatives in October, 1999. If you haven't seen it, it's worth a read (http://www.cato.org/testimony/ct-pm100699.html).
Michaels listed several major conclusions, all of them based on peer-reviewed journal publications. Of most significance are:
* Observed surface warming is far below what the climate models have forecast. Even though the model predictions for future climate have steadily dropped as they become more sophisticated, their predictions have consistently exceeded actual observations.
* Most of the warming has been in winter, and confined to the very coldest airmasses. The warming outside of these airmasses is only 0.2°C per century.
* Climate variation has declined significantly on a global basis while there is no change for precipitation.
* In the United States, streamflow records show that drought has decreased while flooding has not increased.
* Maximum winds in hurricanes that affect the United States have significantly declined, and there is no evidence for a global increase in mid-latitude storms.
* The Kyoto Protocol to the United Nations Framework Convention on Climate Change will have no discernable impact on global climate within any reasonable policy timeframe.
Ten years ago, I believed the modelers that global warming was a serious problem that needed attention and intervention. As I studied the issue year by year, I became less and less convinced that the "problem" was truly serious. My current bottom line: while human activities doubtless influence climate (on a local, regional, and even a global scale), the human-induced climate change from expected increases in greenhouse gases will be a rather small fraction of the natural variations. I don't foresee global warming causing big problems, and believe that even if we controlled every molecule of human emissions we would still see substantial climate change, just as we always have.