Satellite temperature recordAmong these groups are Remote Sensing Systems (RSS) and the University of Alabama in Huntsville (UAH). To compare to the increase from the surface record (of approximately +0.07 °C/decade over the past century and +0.17 °C/decade since 1979) it is more appropriate to derive trends for the lower troposphere in which the stratospheric cooling is removed. In 2001, an extensive, but now somewhat dated, comparison and discussion of trends from different data sources and periods was given in the Third Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) (section 2.2.4). A detailed analysis produced by dozens of scientists as part of the US Climate Change Science Program (CCSP) identified and corrected errors in the satellite data and other temperature observations. The CCSP SAP 1.1 Executive Summary states: The IPCC Fourth Assessment Report Summary for Policymakers states: However, as detailed in CCSP SAP 5.1 Understanding and Reconciling Differences, neither Regression models or other related techniques were reconcilable with observed data.
Some believe that much of the disparity may have been resolved by the three papers in Science, 11 August 2005, which pointed out errors in the UAH 5.1 record and the radiosonde record in the tropics. The satellites also measure the lower stratospheric temperature. The longest data sets of upper air temperature are derived from instruments carried aloft by balloons (radiosondes). One widely reported satellite temperature record, developed by Roy Spencer and John Christy at the University of Alabama in Huntsville (UAH), is currently version 5.2 which corrects previous errors in their analysis for orbital drift and other factors.
The radiosonde data set becomes usably global in about 1958. Globally, the troposphere should warm about 1.2 times more than the surface; in the tropics, the troposphere should warm about 1.5 times more than the surface.
The 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 the RSS and UAH analyses For some time, the UAH satellite data s chief significance was that they appeared to contradict a wide range of surface temperature data measurements and analyses showing warming in line with that estimated by climate models. The 2LT product has gone through numerous versions as various corrections have been applied. 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 process of constructing a temperature record from a radiance record is difficult.
In April 2002, for example, an analysis of the satellite temperature data showed warming of only 0.04 °C per decade, compared with surface measurements showing 0.17 ± 0.06 °C per decade. The use of fingerprinting techniques on data yielded that Volcanic and human-caused fingerprints were not consistently identifiable in observed patterns of lapse rate change. As such, issues with reconciling data and models remain. A potentially serious inconsistency has been identified in the tropics, the area in which tropospheric amplification should be seen.
By comparison, the usable balloon (radiosonde) record begins in 1958. Satellites do not measure temperature as such. Most notably, Mears et al.
The problems with the length of the MSU record is shown by the table below, which shows the UAH TLT (lower tropospheric) global trend (°C/decade) beginning with Dec 1978 and ending with December of the year shown. Likewise, even though they began with the same data, each of the major research groups has interpreted it with different results. Other problems with the radiosondes in addition to the recently discovered solar heating issue could remain in the data. .
A report by the National Research Council that reviewed upper air temperature trends stated: However, the same panel then concluded that As noted earlier, these temperature data, misinterpreted from the satellite data, are now known to have been too low. An important critique of the satellite record is its shortness—adding a few years on to the record or picking a particular time frame can change the trends considerably. Section 1.1 of the CCSP report says: The lower troposphere trend derived from UAH satellites (+0.128 °C/decade) is currently lower than both the GISS and Hadley Centre surface station network trends (+0.161 and +0.160 °C/decade respectively), while the RSS trend (+0.158 °C/decade) is similar.
A longer data series and several corrections to the UAH method leaves the UAH series showing warming, though less than RSS version. For some time the only available satellite record was the UAH version, which showed cooling globally.
As a result, different groups that have analyzed the satellite data to calculate temperature trends have obtained a range of values. (2004), although it must be noted that RSS also has a higher trend when taken only to 2004 (+0.186 °C/decade) In 1996, Hurrell and Trenberth published in the Journal of Climate an analysis showing a warming trend of +0.18 °C/decade from 1979-1995. Using the T2 channel (which include significant contributions from the stratosphere, which has cooled), Mears et al.
There have been complaints of data problems with both records, and difficulty reconciling climate model predictions with the observed data. Climate models predict that as the surface warms, so should the global troposphere. The correction of errors in the analysis of the satellite data, as noted above, have brought the two data sets more closely in line with each other. Christy et al.
of Remote Sensing Systems (RSS) find (through March 2008) a trend of +0.110 °C/decade. The satellite records have the advantage of global coverage, whereas the radiosonde record is longer. (2007) find that the tropical temperature trends from radiosondes matches closest with his v5.2 UAH dataset.
They measure radiances in various wavelength bands, which must then be mathematically inverted to obtain indirect inferences of temperature. at RSS find 0.193 °C/decade for lower troposphere up to July 2005, compared to +0.123 °C/decade found by UAH for the same period. There are ongoing efforts to resolve these differences.
The lack of warming then seen in the records was noted. However, the expected trend in the lower troposphere, given the surface data, would be around 0.194 °C/decade, making the UAH and RSS trends 66% and 81% of the expected value respectively. Since 1979, Microwave Sounding Units (MSUs) on NOAA polar orbiting satellites have measured the intensity of upwelling microwave radiation from atmospheric oxygen.
Satellite temperature measurements have been obtained from the troposphere since 1978. Changes in balloon instrumentation and data processing over the years have been pervasive, however, resulting in discontinuities in these temperature records The radiosondes and the MSU were designed to detect short term changes in temperatures and not long term trends so it would be inappropriate to criticize them for being poor for long term trend detection.
The resulting temperature profiles depend on details of the methods that are used to obtain temperatures from radiances. The intensity is proportional to the temperature of broad vertical layers of the atmosphere, as demonstrated by theory and direct comparisons with atmospheric temperatures from radiosonde (balloon) profiles.
Doing this, through July 2009: An alternative adjustment introduced by Fu et al. 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. In the late 1990s the disagreement between the surface temperature record and the satellite records was a subject of research and debate.
Upwelling radiance is measured at different frequencies; these different frequency bands sample a different weighted range of the atmosphere.