“The U.S. annual (January-December) mean temperature is slightly warmer in 1934 than in 1998 in the GISS analysis (Plate 6). This contrasts with the USHCN data, which has 1998 as the warmest year in the century. In both cases the difference between 1934 and 1998 mean temperatures is a few hundredths of a degree. The main reason that 1998 is relatively cooler in the GISS analysis is its larger adjustment for urban warming. In comparing temperatures of years separated by 60 or 70 years the uncertainties in various adjustments (urban warming, station history adjustments, etc.) lead to an uncertainty of at least 0.1°C. Thus it is not possible to declare a record U.S. temperature with confidence until a result is obtained that exceeds the temperature of 1934 by more than 0.1°C.”
http://pubs.giss.nasa.gov/docs/2001/2001_Hansen_etal.pdf
McIntyre’s discovery was a small error at introduced at the transition between two data sets, correcting for the error does not materially change the observed trends:
It’s also important to understand that temperature does not rise or fall everywhere and equally. In the case of the US, as noted in the paper above:
… it is clear that the post-1930s cooling was much larger in the United States than in the global mean. The U.S. mean temperature has now reached a level comparable to that of the 1930s, while the global temperature is now far above the levels earlier in the century. The successive periods of global warming (1900-1940), cooling (1940-1965), and warming (1965-2000) in the 20th century show distinctive patterns of temperature change suggestive of roles for both climate forcings and dynamical variability.”
Here is the “global” picture:
Some people really, really want to believe that some major statistical error is going to be discovered tomorrow which demonstrates that such trends are a mirage. It’s not going to happen – these trends have been established on the basis of several different sorts of terrestrial and satellite data, and as the data has been refined data sets are rapidly converging. In this regard it's quite telling that observers such as the author of this article are reduced to claims that the increasingly minor nature of the errors discovered and the corrections made suggest that skepticism is increasingly justified.