The Data v. A Statistic: TWTW is not enamored with the reporting of global air surface temperatures with a single statistic, such as a global average. Causes of concern include issues with air-surface instruments, the likelihood that minimum temperatures have been increasing with slight changes in the surrounding area, and the frequent manipulation of the data by reporting agencies without clear justification for the manipulation. In addition, the single statistic buries the global composition of the warming / cooling. As the satellite data show, the warming is concentrated in the northern part of the Northern Hemisphere. Please see: http://nsstc.uah.edu/climate/2011/November/trend_Dec78_Nov11_alt.png
Even with satellite data there is a tendency to develop a trend using regression analysis or similar tools. An examination of the historic satellite data itself shows two long periods of no warming trend separated by period of discontinuity. The exact dates of the discontinuity depend upon the views of the researcher, but they are around the time of the great El Niño of 1998 or shortly thereafter. This discontinuity is a jump in the average temperature anomaly from -0.1 deg C to +0.1 deg C. The cause of this discontinuity should be a subject of great interest, but it is lost to the Climate Establishment. Please see: Global Temperature Report :: UAHuntsville.
this is a precise restatement of my position on global temps and the satellite record. many people think El Nino and La Nina are opposite phases of the same system but they are not.