Radiosonde measurements (from around 400 stations) of the troposphere up to the year 2002, and satellite-borne
microwave sounding unit measurements, both showed temperatures at heights between 1 and 8 km to be around
0.25 °C above the 1981 to 2000 average. This reference period was chosen to reflect the period covered by the
satellite measurements.
[Note: the satellite record is still relatively short (only since 1979), so it is statistically difficult to infer a global warming
trend or any long-term trend from such data. In such a short data set, a trend depends upon the start and end years. Two
decades is not enough. In other words, a trend over such a short period is inadequate to diagnose the period that matters (pre-industrial
(about 1750) to present). The surface station record 1860-2003 shows a clear signature of global warming because it is a much longer record
and is not subject to start/end year sampling bias.].

Figure source: UK Hadley Centre for Climate Prediction and Research  report: "Climate change observations and predictions: Recent research on climate change science from the Hadley Centre" December 2003

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