Upper Air - Annual 2011
During the past century, global surface temperatures have increased at a rate near 0.08°C/decade (0.14°F/decade), but this trend has increased to a rate of approximately 0.17°C/decade (0.31°F/decade) during the past 30 years. There have been two sustained periods of warming, one beginning around 1910 and ending around 1945, and the most recent beginning about 1976. Temperatures during the latter period of warming have increased at a rate comparable to the rates of warming projected to occur during the next century with continued increases of anthropogenic greenhouse gases.
Temperature measurements have also been made above the Earth's surface over the past 54 years using balloon-borne instruments (radiosondes) and for the past 33 years using satellites. These measurements support the analyses of trends and variability in the troposphere (surface to 10-16 km) and stratosphere (10-50 km above the earth's surface).
The best source of upper air in-situ measurements for studying global temperature trends above the surface is the Radiosonde Atmospheric Temperature Products for Assessing Climate (RATPAC) dataset.
Data collected and averaged between the 850–300 mb levels (approximately 5,000 to 30,000 feet above the surface) indicate that 1958–2011 global temperature trends in the middle troposphere are similar to trends in surface temperature; 0.13°C/decade (0.23°F/decade) for surface and 0.15°C/decade (0.27°F/decade) for mid-troposphere. Since 1976, mid-troposphere temperatures have increased at a rate of 0.17°C/decade (0.31°F/decade). For 2011, global mid-troposphere temperatures were 0.34°C (0.61°F) above the 1971–2000 mean—the ninth warmest on record.
Since 1979, NOAA's polar orbiting satellite measurements have also been used to measure temperatures in the troposphere and stratosphere. Microwave Sounding Unit (MSU) data are analyzed for NOAA by the University of Alabama in Huntsville (UAH), Remote Sensing Systems (RSS, Santa Rosa, California) and the University of Washington (UW). These observations show that the global average temperature in the middle troposphere (the layer which is centered at an altitude of 2 to 6 miles, but which includes the lower stratosphere) has increased, though differing analysis techniques have yielded similar but different trends (see below).
In all cases these trends are positive. The analysis performed by RSS reveals a trend of 0.08°C/decade (0.15°F/decade) while the UAH analysis reveals a lower trend of 0.05°C/decade (0.09°F/decade). When adjusted by University of Washington scientists to remove the stratospheric influences from the RSS and UAH mid-troposphere average, the trends increase to 0.14°C/decade (0.25°F/decade) and 0.11°C/decade (0.20°F/decade), respectively. (A journal article is available that describes the University of Washington adjustments to remove the stratospheric influence from mid-troposphere averages.) Trends in these MSU time series are similar to the trend in global surface temperatures, which increased at a rate near 0.15°C/decade (0.28°F/decade) during the same 33-year period.
While middle tropospheric temperatures reveal an increasing trend over the last three decades, stratospheric temperatures (14 to 22 km / 9 to 14 miles above the surface) have been below average since the warming effects from the 1991 Mt. Pinatubo eruption dissipated in 1993. January-December 2011 was the 18th consecutive year with below-average temperatures (an anomaly of -0.41°C/-0.74°F), tied with 2000 as the third coolest year on record. The below-average stratospheric temperatures are consistent with the depletion of ozone in the lower stratosphere and the effects of increasing greenhouse gas concentrations. The large temperature increase in 1982 is attributed to the volcanic eruption of El Chichon, and the increase in 1991 was associated with the eruption of Mt. Pinatubo in the Philippines.