Satellite Temperature Measurements - Trends From The Record

Trends From The Record

See also: UAH satellite temperature dataset and MSU temperature measurements

Year	UAH Trend
1991	0.087
1992	0.024
1993	-0.013
1994	-0.003
1995	0.033
1996	0.036
1997	0.040
1998	0.112
1999	0.105
2000	0.095
2001	0.103
2002	0.121
2003	0.129
2004	0.130
2005	0.139
2006	0.140
2007	0.143

Records have been created by merging data from nine different MSUs, each with peculiarities (e.g., time drift of the spacecraft relative to the local solar time) that must be calculated and removed because they can have substantial impacts on the resulting trend. The satellite record is short, which means adding a few years on to the record or picking a particular time frame can change the trends considerably. The problems with the length of the MSU record is shown by the table to the right, which shows the UAH TLT (lower tropospheric) global trend (°C/decade) beginning with Dec 1978 and ending with December of the year shown.

The process of constructing a temperature record from a radiance record is difficult. The satellite temperature record comes from a succession of different satellites and problems with inter-calibration between the satellites are important, especially NOAA-9, which accounts for most of the difference between various analyses. NOAA-11 played a significant role in a 2005 study by Mears et al. identifying an error in the diurnal correction that leads to the 40% jump in Spencer and Christy's trend from version 5.1 to 5.2. There are ongoing efforts to resolve differences in satellite temperature datasets.

Christy et al. (2007) find that the tropical temperature trends from radiosondes matches closest with his v5.2 UAH dataset. Furthermore, they assert there is a growing discrepancy between RSS and sonde trends beginning in 1992, when the NOAA-12 satellite was launched. This research found that the tropics were warming, from the balloon data, +0.09 (corrected to UAH) or +0.12 (corrected to RSS) or 0.05 K (from UAH MSU; ±0.07 K room for error) a decade.

Using the T2 channel (which include significant contributions from the stratosphere, which has cooled), Mears et al. of Remote Sensing Systems (RSS) find (through January 2012) a trend of +0.082 °C/decade. Spencer and Christy of the University of Alabama in Huntsville (UAH), find a smaller trend of +0.046 °C/decade.

A no longer updated analysis of Vinnikov and Grody found +0.20°C per decade (1978–2005). Another satellite temperature analysis is provided by NOAA/NESDIS STAR Center for Satellite Application and Research and use simultaneous nadir overpasses (SNO) to remove satellite intercalibration biases yielding more accurate temperature trends. The SNO analysis finds a 1979-2011 trend of +0.128°C/decade for T2 channel.

Lower stratospheric cooling is mainly caused by the effects of ozone depletion with a possible contribution from increased stratospheric water vapor and greenhouse gases increase. There is a decline in stratospheric temperatures, interspersed by warmings related to volcanic eruptions. Global Warming theory suggests that the stratosphere should cool while the troposphere warms

The long term cooling in the lower stratosphere occurred in two downward steps in temperature both after the transient warming related to explosive volcanic eruptions of El Chichón and Mount Pinatubo, this behavior of the global stratospheric temperature has been attributed to global ozone concentration variation in the two years following volcanic eruptions.

Since 1996 the trend is slightly positive due to ozone recover juxtaposed to a cooling trend of 0.1K/decade that is consistent with the predicted impact of increased greenhouse gases.

The process of deriving trends from SSUs measurement has proved particularly difficult because of satellites drift, inter-calibration between different satellite with scant overlap and gas leak in the instrument carbon dioxide pressure cell, furthermore since the radiances measured by SSUs are due to emission by carbon dioxide the weighting functions move to higher altitudes as the carbon dioxide concentration in the stratosphere increase. Mid to upper stratosphere temperature show strong negative trend interspersed by transient volcanic warming after the explosive volcanic eruptions of El Chichón and Mount Pinatubo, little temperature trend has been observed since 1995. The greatest cooling occurred in the tropical stratosphere consistent with enhanced Brewer-Dobson circulation under greenhouse gas concentrations increase.

Channel	Start	End Date	RSS Global Trend (K/decade)	UAH Global Trend (K/decade)	STAR v2.0 Global Trend (K/decade)
MSU
TLT	1979	2012-01	0.137	0.136
TMT	1979	2012-01	0.082	0.046	0.128
TTS	1987	2012-01	-0.008
TUT	1981	2012-01			0.039
TLS	1979	2012-01	-0.303	-0.382	-0.326
SSU
TMS	1978-11	2006-04			-1.007
TUS	1978-11	2006-04			-0.927
TTS	1979-07	2006-04			-1.236