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A history of satellite measurements of global warming

Posted on 12 September 2010 by dansat

John Christy and Roy Spencer of the University of Alabama published a series of papers starting about 1990 that implied the troposphere was warming at a much slower rate than the surface temperature record and climate models indicated Spencer and Christy (1992). One early version of their data even showed a cooling trend (Christy et al. 1995).

Several groups of scientists began looking closely at this discrepancy. With so many other pieces of evidence indicating warming, it seemed unlikely that the troposphere would not be warming. Errors were discovered in the methods the UAH group used to adjust the data.

To understand what was wrong: The satellites must pass over the same spot on Earth at the same time each day to get a temperature average. In reality the time the satellite passes drifts slightly as the orbit slowly decays. To compensate for this and other orbital changes a series of adjustments must be applied to the data.

Temperature trends of the troposphere now match well with the surface based trend.

The MSU satellite data is collected from a number of satellites orbiting & providing daily coverage of some 80% of the Earth's surface. Each day the orbits shift and 100% coverage is achieved every 3-4 days. The microwave sensors on the satellites do not directly measure temperature, but rather radiation given off by oxygen in the Earth's atmosphere. The intensity of this radiation is directly proportional to the temperature of the air and is therefore used to estimate global temperatures.

There are also differences between the sensors that were onboard each satellite and merging this data to one continuous record is not easily done. It was nearly 13 years after the orginal papers that the adjustments that Christy and Spencer originally applied were found to be incorrect. Mears et al. (2003) and Mears et al. (2005).

When the correct adjustments to the data were applied the data matched much more closely the trends expected by climate models. It was also more consistent with the historical record of troposphere temperatures obtained from weather balloons. As better methods to adjust for biases in instruments and orbital changes have been developed, the differences between the surface temperature record and the troposphere have steadily decreased.

At least two other groups keep track of the tropospheric temperature using satellites and they all now show warming in the troposphere that is consistent with the surface temperature record. Furthermore data also shows now that the stratosphere is cooling as predicted by the physics.

All three groups measuring temperatures of the troposphere show a warming trend. The U.S. Climate Change Science Program produced a study in April 2006 on this topic. Lead authors included John Christy of UAH and Ben Santer of Lawrence Livermore National Labs. The first page has this quote:

"Previously reported discrepancies between the amount of warming near the surface and higher in the atmosphere have been used to challenge the reliability of climate models and the reality of human-induced global warming... This significant discrepancy no longer exists because errors in the satellite and radiosonde data have been identified and corrected. New data sets have also been developed that do not show such discrepancies."

There are still some discrepancies between satellite measured temperatures in the tropics and those measured by radiosondes. Most researchers believe this difference is likely due to instrument errors.

The original discrepancy is an excellent example of how science works and of critical thinking. With many different indicators showing warming, it did not make sense that the troposphere would be cooling. This discrepancy was taken very seriously by the scientific community, and the consistency and accuracy of all relevant data were examined intensely.

Science advances by trial and error. The result is an increased knowledge of how to measure the temperature of the troposphere from space.

This post is the Basic version (written by Dan Satterfield) of the skeptic argument "Satellites show no warming in the troposphere".

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Comments 1 to 15:

  1. Spencer and Christy get a lot of flak from many quarters but the UAH data set and satellite data sets generally are proving a really usefull tool for analysing the climate. While I disagree with their conculsions they have produced some really interesting science.
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  2. John Christy and Roy Spencer have been quite vocal on the web with theories and never-proven affirmations which really cast a big shadow of doubt on their scientific intentions - their mistake described above has fueled the denier movement for like over 10 years and they are now promoting (on the web) equally strange theories, so I would also recommend this post - Should you believe anything John Christy and Roy Spencer say?
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  3. Their first report, with the rubric ”Precise Monitoring of Global Temperature Trends from Satellites”, was published in Science in March 1990, and showed a rather high level of self-confidence. Here are some interesting quotes: ”Our data suggest that high-precision atmospheric temperature monitoring is possible from satelite microwave radiometers. Because of their demonstrated stability and the global coverage they provide, these radiometers should be made the standard for the monitoring of global atmospheric temperature anomalies since 1979.” ”Various computerized climate models, which predict future changes through time-dependent equations representing physical processes, can now be evaluated with accurate global temperature measurements.” ”These improvements should facilitate more informed policy decisions concerning the effects of anthropogenic greenhouse gas production.”
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  4. I'm not going to make any accusations pertaining to the reasoning behind the error not being discovered... but I have to say that I bet mears et al. off the record had some very interesting things to say...
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  5. No Robert, please don't. That's the kind of garbage spewing all over from sites like WUWT or CA, we don't need that here. Everybody should refrain from implying or suggesting anyting. I've been guilty of it in the past myself and I'm not proud of it, it should not be welcome on this site. This posts does a decent job of presenting some facts, let's leave it at that. Each can have his/her own opinion as to what the deeper significance is, keep it to yourself until you have something really solid to substantiate. What's more interesting, IMO, is that it provides an instance of models vs data in which the models were right. That is one characteristic of models based on physics. When data don't agree, it is ground for looking more closely at both, but well established physical models must not be considered worthless only because on set of data comes along that happens to disagree with model expectations.
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  6. The reason the troposphere is not warmoing as quickley as the rest of the atmosphere is because it contains the methane gas layer within it. gas distribute in opur atmosphere according to weight. methane lies right next to water vapor and is at the required prssure to get its leg on with oits ability to take up heat into its moleclues in order to form its hydrate in the sky. this hydrate formation is what causes lightening they discovered in 2007. During hydrate formation of ice crystals or hail if the moisture in the clouds(water vapor) is great enough, it grabs all the positive ions and this creats electricity. All our DOE money should be going to devlop this source of power . . .water and methane and pressure and in te interim tidal power to replace fossil fuel until it can be im[plmented. That's the plan and the only plab that can save us.
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  7. General thoughts not aimed at this article or anyone in particular: Roy Spencer and John Christy are real skeptics and real scientists - a far cry from greenhouse-disbelieving psuedo-skeptic blog types. They argue that climate sensitivity is low. That's perfectly valid if they can argue the case scientifically. Spencer published a paper recently on the matter so his ideas cannot be obviously wrong and he must be contributing to the field. Yes there was a UAH satellite correction, but records sometimes encounter large errors. That's science. You shouldn't read conspiracy into it. As such their honesty is unquestionable. I disagree with them on climate sensitivity, I think the charney sensitivity range is more likely because that is what model and paleoclimate studies of sensitivity invariably show. But it's perfectly fine for scientists to challenge this with new ideas. If they can convince countless scientists that their idea is right then I would inevitably change my mind too. Spencer and Christy fit this role. All I am saying is that bashing Spencer and Christy is baseless and resembles the typical scientist-bashing behavior seen at WUWT imo.
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  8. ...Which leads to...We should be grateful that two climate skeptics are in charge of a set of global temperature measurements. Other skeptics and deniers are compelled to accept that global temperatures are increasing, because they're saying it.
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  9. wingding, when a scientist says that creationism is more scientifically grounded than evolution I'm sorry, but it is just NOT "baseless" to suggest that they might not be entirely objective. Consider Spencer and Christy in their own words. The one indoctrinating Sunday school kids in 'anti environmentalist' rhetoric and the other arguing that evolution is unfounded science pushed by non-Christian religions. Yes, when presented with overwhelming evidence of errors they have adjusted their results. Yes, other than the evolution bit, they accept the basic fundamentals of science. That this makes them 'the reasonable skeptics' is a very sad commentary on the nature of the debate.
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  10. @ Dan Satterfield One the first rules of writing articles about technical subjects for the general public is to define all acronyms the first time they are used. For example, insert "(UAH)" immediately after the words, University of Alabama at Huntsville" in the first sentence. Also, the graph is also meaningless unless the reader knows what "RSS" and "UAH" mean. Insert the definitions into the graph. Some readers will only look at the graph and not read the text.
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  11. Further to the acronym comment, can we have the expansion of MSU please. It's really hard to cover the enormous range of knowledge and background that comments to this and other climate change sites reveal. Thanks very much to all who are working at it.
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  12. wingding #7, I disagree that criticisms of Spencer and Christy as scientists are baseless. I had linked to articles quoting them making what I consider blatantly unscientific / biased / false statements as evidence of this, but it was apparently deleted. Which seems somewhat overzealous to me. It was certainly no less polite than, for instance, comparing people who denounce Spencer and Christy to the "behavior seen at WUWT".
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  13. Some time ago, in order to understand this, I plotted the GISS Model E (upper-left) versus the RATPAC sonde data (lower-left), the RSS MSU (upper-right) and the UAH MSU (lower-right)
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  14. "Further to the acronym comment, can we have the expansion of MSU please." MSU is the Microwave Sounding Unit. It is a measurement system of radiometers which, not surprisingly sample electromagnetic energy in the 'microwave' portion of the spectrum. The National Oceanic and Atmospheric Administration (NOAA) has operated satellites which have had various generations of MSU instruments on them since late 1978. The MSU samples energy that is emitted by oxygen atoms. The theory of operations is that the higher the temperature at a given region of the atmosphere the greater the energy that will be received at the satellite. The energy at this wavelength is not particularly large in terms of earth's energy budget, but the unique nature of the emissions in theory makes it suitable as a temperature record.
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  15. A discussion regarding the ability of satellite instruments to detect TOA IR radiation may shortly arrive here. Here's some information on how instruments are calibrated: CERES Instrument Overview / Calibration
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