Arguments
Satellite measurements of warming in the troposphere
What the science says...
| Select a level... |
Basic
|
Intermediate
|
Advanced
| ||||
|
The most recent satellite data show that the earth as a whole is warming. |
|||||||
Climate Myth...
Satellites show no warming in the troposphere
"Satellite measurements indicate an absence of significant global warming since 1979, the very period that human carbon dioxide emissions have been increasing rapidly. The satellite data signal not only the absence of substantial human-induced warming but also provide an empirical test of the greenhouse hypothesis - a test that the hypothesis fails." (Bob Carter)
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.
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 (pdf) 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.
Last updated on 24 July 2015 by David Kirtley. View Archives
I find it interesting that Dr. Roy Spencer gets a lot of (mostly deserved) criticism here for his interpretation of temperature data, and all the corrections to the UAH temperature data. Yet what really puzzles me is that when I visited Dr. Cowtan's Temperature trends site
http://www.ysbl.york.ac.uk/~cowtan/applets/trend/trend.html
ALL the global, land/ocean, satellite data sets show about +1.4°C ± 0.2°C/decade warming for the past 20 years, EXCEPT for RSS, which is only +0.04°C per decade in that time frame. Similarly, at 30 years, the average warming is about 0.175°C/decade and RSS remains noticably lower than the other sets. So it seems all the agjustments to UAH have brought it more in agreement with the surface data, but it does beg the question what's with RSS?
[PS] Fixed link
I dont think there is criticism of S&C for adjusting satellite data - given changes in satellite, sensors available, orbits etc, there would be problems if they didnt. There is criticism of those who think satellites are better than surface records because they believe they are adjusted less, and also fof S&C because of their stalling in releasing source code and algorithms.
RSS has been under suspicion for some time, and see for example analysis here. It will be interesting to see how the MSU indexes respond to the El Nino since in the past, there has been very strong tropospheric response to ENSO. Radiosondes will provide another measure of that response so we have another way to validate the MSU indexies.
Roy just posted Nov data for UAH, and it's starting to show a spike.
Something I'm having trouble reconciling is the comparison of UAH and RSS datasets. The article states, "Throughout the history of Tropospheric temperature measurement, the UAH analysis has always been lower than RSS for all temperature products." However, as Knaugle pointed at #51, it's RSS that's been the outlier, or at least it was until UAH 6.0 brought UAH into line with it. Spencer (of UAH) talks about the discrepancy in a blog post from a few years back, promising he's not been "bought off by Greenpeace", and even going so far as to say that in his boss's (John Christy) opinion, "RSS data is undergoing spurious cooling."
GregCharles is correct about UAH 6.0. It also points out the need for several popular web sites to "get with the times". Whatever the reason UAH 6.0 was adjusted, the effect was to make it nearly identical to RSS. This improves "consistency", but begs the question why UAH thought RSS right and everyone else wrong. Regardless, all the popular sites I visit still rely on older UAH 5.6 or thereabouts, and we are now left with the satellite data showing nearly no warming for the past 20 years, and the surface data sets with more significant warming. The clear discrepancy between RSS & UAH 6.0 and the surface data (GISS, HadCrut4, Berkeley, etc) is something this site should address and I'm not seeing it.
To add, bear in mind the denier mantra
"Satellites are true and NOAA lies."
is something I increasingly have trouble arguing against even considering the 10 positive indicators of a warming world show the idea we have not really warmed in 20 years makes no sense. But, satellites don't lie, right?
[Rob P] - It's informative to look at the satellite trend (for RSS) for the lower troposphere:
So the satellite data does in fact show a long-term warming trend. If one selects the super El Nino of 1997/1998 as a starting point it's possible to fool the uninformed, but that deceptive practice may soon come to an end with the current super El Nino likely to anomalously warm the lower troposphere in the next 4-5 months.
I agree with the RSS showing long term warming. However, the claim from the "skeptics" is no warming since 1998. If you throw out 1998 and look at the past 15 years, 2000.9 to present (that "escallator thing", RSS and now UAH 6.0 show cooling). So long as that is the case, politicians like Lamar Smith will simply claim NOAA is fudging the numbers. I do find it curious that UAH has adjusted its data about as often as any other entity out there with a temperature data set while RSS seems rather mum on versioning. Yet whenever NOAA adjusts its data set, it's called "fraud".
Note also that back in 2013, RSS was very unapologetic in declaring that most all the climate models are "wrong" and their graphs claim the breakout occurred around 2000, not 1998.
http://www.remss.com/research/climate
Finally from Dr. Cowtan's temperature plotter, the warming from the satellites is
0.122 C/decade since 1979 as was shown,
but 20 year and 15 year trends show
0.037 C/decade since Dec. 1995 and
-0.017 C/decade since Dec. 2000.
So interestingly while deniers bank all on the 1998 El Nino, we do need to avoid the mistake of expecting much from the current one as a fix.
We will know if the current super El Nino is affecting the satellite record like the super El Nino of 1997/1998 when the December & January data come in - assuming the behaviour is similar to past El Nino.
As for Kevin Cowtan's Skeptical Science calculator - note the error bars are orders of magnitude larger than the trend, so there is no statistical basis for any claim that it has cooled. The time period is too short and the interannual variation (standard deviation) too large. We would need a longer time period in order to establish statistical significance. Note that contrarians never attempt this, they simply make a claim without supporting evidence.
It would be interesting to find out why the satellite data 'overreacts' to El Nino and La Nina though. Is this a real phenomenon occurring in the lower troposphere? Or is this an artefact which all the processing fails to remove from the microwave soundings?
Eli has a great post on UAH's flaws, by a satellite engineer who gives lots of details: UAH TLT Series Not Trustworthy.
Even Roy Spencer now admits that satellite "measurements" of tropospheric temperature cannot and must not be used as proxies for surface temperature measurements, due to major unresolved issues in the assumptions used in the complex conversions of the microwave measurements into estimates of temperatures. (Spencer is one of the two main people responsible for the "UAH" satellite-based troposphere temperature estimations.)
Tom Dayton,
I saw you post this on David Appell's site and was looking for an appropriate place to ask this question at skepticalscience. Would it be possible for you to explain the connection between total precipitable water and microwave emission from oxygen molecules that casts doubt on the calculation of tropospheric temperature. I am not following the discussion between ehak and Spencer at the site you linked to.
Sorry, JoeT, I haven't tried to understand Roy Spencer's admission of the satellite-based estimate of tropospheric temperature being not usable as a proxy for surface temperature. I don't have time right now, since I'd have to spend a lot of time to research it. I posted that just because it's informative that even Spencer has admitted it.
The Earth's surface is in a warming trend, somewhat as predicted.
The stratosphere is in a cooling trend, as predicted.
So would not there be a "Goldilocks Layer" in between, with no trend at all?
Could that Goldilocks Layer be the middle troposphere?
So "No warming, since forever." can be the denialists' mantra.
sailingfree
Take a look at the RSS site here.
Select different dataseries to show different heights. The graph on the left for each one is the Weighting Function. Essentially how much of the signal for that channel originates from different levels of the atmosphere. Irrespective of whether there is an actual Goldilocks layer at altitude, there is a blurring of our ability to measure it due to the physics of radiation transfer.
64 Glenn, Thanks. My point is, good data or bad data, a denier would not care, as long as he could show data for the "goldilocks layer".
Why is "T1, MSU Channel 1" which is "peaking near ground level" seldom used?
I'm talking to a guy who seems to be claiming the satellites show half or less as much warming as the "land" temperature record. So I would be interested to see a land temperature reconstruction from the satellites to find out if there's any truth to that. Do clouds prevent an accurate reconstruction of ground temperatures by satellites?
Qwertie @66 , his "peaking near ground level" description is simply false.
The satellite data (usually quoted by Spencer as the so-called The Lower Troposphere) averages out over much of the height of the troposphere — and with a small amount of stratosphere added to the mixture as well !! [a bias which they attempt to remove]
It could be taken as equivalent to the temperature on top of a very tall mountain. But is he seriously suggesting that way-up-high mountain-peak temperatures are in any way a reasonable representation of the world's ground-level & sea-level temperature? He is pulling your leg (or his own).
Perhaps his next comment will be that we should only look at the warming trend measured at Mt Everest Base Camp ;-)
Eclectic @67, the AMSU comes with a variety of channels. T2 in the diagram below is used for the middle troposphere (TMT) and by some mathematical manipulations relating to the difference in weighting between nadir and limit scanners, also for the lower troposphere (TLT). Channel T1 is not used for any of the standard temperature products, but does indeed peak near the Earth's surface.
I am unaware of why it is not used for a temperature record, but it may not have appeared on all satellites over the satellite era, or the AMSU era, making a continuous record impossible. It may also not be able to handle changes in surface altitude without significant distortion. Somebody more expert on the subject may well be aware of other potential reasons, or indeed, may know the actual reason rather than merely conjecturing.
Indeed, I speculate/conjecture that the satellite record achieves its "lowermost" layer of tropospheric temperature, by lateral scanning compounded with vertical scanning — such that the horizontal resolution is so poor it has difficulty differentiating very elevated land from near-sea-level land. In other words, T1 channel has low validity.
It would be interesting to hear an expert opinion on the realities of the "lowermost" section of the measurements.
Either way, the satellite recordings (even apart from their manifold problems) have some value in studying the upper atmosphere — but little value in studying surface temperatures. But in providing some distraction from actual surface temperatures [including ocean-warming and ice-melting] they provide a modicum of illusory comfort to climate change deniers.
A primer on both surface and satellite temperature records:
Satellite-measurements-warming-troposphere-advanced
Primer-Tropospheric-temperature-measurement-Satellite
A-history-of-satellite-measurements-of-global-warming
Why-we-can-trust-the-surface-temperature-record
Assessing-global-surface-temperature-reconstructions
Microsite-influences-on-global-temperature-intermediate
Dropped-stations-introduce-warming-bias-intermediate
OfAveragesAndAnomalies_pt_1A
OfAveragesAndAnomalies_pt_1B
OfAveragesAndAnomalies_pt_2A
OfAveragesAndAnomalies_pt_2B
Eschenbach_satellite_part
James-Taylor-Forbes-UAH-rebuttal
New_Research_Special_Satellites
Surface_Temperature_Or_Satellite_Brightness
http://www.realclimate.org/index.php/data-sources/
Arent the low frequency channels used for water vapour not temperature?
A little background info about the updated TLT data from RSS.
The temperature trend now matches the surface records pretty well.