Posted on 08/16/2005 11:14:50 AM PDT by cogitator
In one of a trio of new global warming papers in Science, Mears & Wentz (2005) address what they consider to be a large source of uncertainty in our (University of Alabama in Huntsville, "UAH") satellite estimate for global lower tropospheric ("LT") temperature trends since 1979. The satellite measurements come from the Microwave Sounding Units (MSUs) and Advanced Microwave Sounding Units (AMSUs) flying on NOAA's polar orbiting weather satellites. The UAH estimate of the globally averaged trend since 1979 to the present has been +0.09 deg. C/decade, considerably below the surface thermometer estimate that has been hovering around +0.20 deg. C/decade for the same period of record.
This discrepancy between the UAH satellite LT trends and the surface thermometer trends has caused some consternation, since what we understand of atmospheric physics suggests that sustained warming at the surface should be amplified with height in the troposphere, not reduced.
Mears & Wentz, who are very capable remote sensing experts from Remote Sensing Systems ("RSS", Santa Rosa, California), found that the LT trend was particularly sensitive to the UAH method for removing the drift of the satellites through the local observing time. The satellites are launched into sun-synchronous orbits that are meant to cross over the same Earth locations at approximately the same time each day. But since the satellites do not have on-board propulsion, the satellites fall slowly back to Earth, which changes their orbital characteristics. In particular, what began as early afternoon observations from the daylight side of the "afternoon satellites" orbits drift to later in the day over the several years of each satellite's lifetime. This causes a spurious cooling trend as the Earth observations are made later in the afternoon to the evening.
The UAH method for removing this drift depended upon the spacecraft roll attitude (the accuracy with which it was pointing straight down, and not sideways) being almost exactly the same during the day side of the orbit as the night side. The new research paper presents Mears & Wentz's own estimate of LT trends using diurnal cycle corrections based upon a climate model estimate of the daily (diurnal) cycle of temperature at different levels in the atmosphere, on a global basis.
Their final estimate of the global lower tropospheric trend through 2004 is +0.19 deg. C/decade, very close to the surface thermometer estimate, and this constitutes the primary news value of their report.
While their criticism of the UAH diurnal cycle adjustment method is somewhat speculative, Mears & Wentz were additionally able to demonstrate to us, privately, that there is an error that arises from our implementation of the UAH technique. This very convincing demonstration, which is based upon simple algebra and was discovered too late to make it into their published report, made it obvious to us that the UAH diurnal correction method had a bias that needed to be corrected.
Since we (UAH) had already been working on a new diurnal adjustment technique, based upon the newer and more powerful AMSUs that have been flying since 1998, we rushed our new method to completion recently, and implemented new corrections. As a result, the UAH global temperature trends for the period 1979 to the present have increased from +0.09 to +0.12 deg. C/decade -- still below the RSS estimate of +0.19 deg. C/decade.
Our new AMSU-based (observed) diurnal cycle adjustments end up being very similar to RSS's climate model (theoretical) adjustments. So why the remaining difference between the trends produced by the two groups? While this needs to be studied further, it looks like the reason is the same as that determined for the discrepancy in deep-tropospheric satellite estimates between the two groups: the way in which successive satellites in the long satellite time series are intercalibrated. There has been a continuing, honest difference of opinion between UAH and RSS about how this should best be done.
In a paper accompanying the Mears and Wentz paper, a new analysis of radiosonde (weather balloon) data by Sherwood et al. also obtains larger levels of warming than have been previously reported. No other radiosonde dataset that has attempted to adjust for the calibration artifacts discussed therein has produced warming estimates as high as those obtained in this new study. As is always the case, it will take a while for the research community to form opinions about whether the new radiosonde adjustments advocated in this work are justified. At a minimum, the new work shows that at least one method for analysis of the weather balloon data (which have traditionally supported the much smaller satellite trends from UAH) results in trends much closer to the warmer surface thermometer trends.
The third paper (Santer et al, 2005) takes a more thorough look at the theoretical expectation that surface warming should be amplified with height in the troposphere. The authors restate what had already been known: that the UAH satellite warming estimates were at odds with theoretical expectations (as had been some radiosonde measures). Now, the convergence of these newly reported satellite and radiosonde estimates toward the surface warming estimates, if taken at face value, provides better agreement with climate models' explanation of how the climate system behaves.
What will all of this mean for the global warming debate? Probably less than the media spin will make of it. At a minimum, the new reports show that it is indeed possible to analyze different temperature datasets in such a way that they agree with current global warming theory. Nevertheless, all measurements systems have errors (especially for climate trends), and researchers differ in their views of what kinds of errors exist, and how they should be corrected. As pointed out by Santer et al., it is with great difficulty that our present weather measurement systems (thermometers, weather balloons, and satellites) are forced to measure miniscule climate trends. What isn't generally recognized is that the satellite-thermometer difference that has sparked debate in recent years has largely originated over the tropical oceans -- the trends over northern hemispheric land areas, where most people live, have been almost identical.
On the positive side, at least some portion of the disagreement between satellite and thermometer estimates of global temperature trends has now been removed. This helps to further shift the global warming debate out of the realm of "is warming happening?" to "how much has it warmed, and how much will it warm in the future?". (Equally valid questions to debate are "how much of the warmth is man-made?", "is warming necessarily a bad thing?", and "what can we do about it anyway?"). And this is where the debate should be.
Excellent points, Dr. Spencer.
If there is global warming, it is probably responsible for delaying the Ice Age that has been overdue for a couple thousand years.
Good post Cog, and good analysis. There are several factors to this global warming debate, I'd like to see them all discussed and considered.
Most of these questions have a simple answer. The Sun. The Sun has more of an effect on our surface temperature than anything that we could possibly do to this planet.
We had that Ice Age 30 years ago, remember? At least, that's what these same "scientists" were telling us.
There is no global warming, at least in the sense that the ecofreaks mean it. They intend to suggest that temperatures are in a permanent warming trend. The historical data says that these things are cyclical. It seems that we're in a warm part of the cycle right now, but whterh in 30 years or 100 or 1000, the tempreatures will turn the other way -- and the liberals/leftists of that time will try to scare us into believing that we're allgoing to freeze in the middle of a personalized iceberg. Unfortunately, they'll have some "scientists" supporting them (in search of research grants.)
There is no global warming, at least in the sense that the ecofreaks mean it. They intend to suggest that temperatures are in a permanent warming trend. The historical data says that these things are cyclical. It seems that we're in a warm part of the cycle right now, but whterh in 30 years or 100 or 1000, the tempreatures will turn the other way -- and the liberals/leftists of that time will try to scare us into believing that we're allgoing to freeze in the middle of a personalized iceberg. Unfortunately, they'll have some "scientists" supporting them (in search of research grants.)
Doesn't matter, doesn't matter and little to none.
RE: Surface measurements: How much of the apparent measurement of slight warming is due to the expansion of high IR reflection surface modifications (due to urbanization expansion and development in rural areas) and the increase in energy dissipation induced by electrical and electromagnetic human created signals and currents? To what extent does the fact the most measurement stations are in urban areas that were far less urban 100 years ago or if not, near roads that went from dirt to paved, have an impact? To what extent does the overconcentration of measurement stations in Eastern North America and Western Europe play a role? Do we understand all sources of variation in our measurement systems? Do we understand what the expected "natural" level of variation is? Have we made extensive use of Monte Carlo Modelling of the measurement systems? Do we truly have an ability to extract a meaningful signal from noise in our measurement system? Do we understand all sources of measurement bias and other extenuating circumstances to the level required for proper correction factors to be employed? Etc ....
Actually, it's about as complete and total a climb-down and retraction as I've ever seen. That's what you do, you 'readjust' your calculations, and show that what you were really saying is what everyone else was saying too. I'm afraid what remains of the scientific controversy about the reality of global warming just about vanished. But I agree the real questions should be 'is it a overall a bad thing?' and 'what practical things can we do to ameliorate the local bad effects?'
That's true. However, to the best that can be determined from the data, the Sun's output has remained relatively constant over the past 30 years, while the Earth's surface and atmosphere have warmed. There's more about this here:
While Spencer has been a skeptical voice, he's been a "refined" voice (despite some peevishness about the peer-review process). When your results finally end up within the error bars of the predictions, it's perfectly good practice to say so. Unfortunately, earlier results of the UAH-NASA group (Christy at UAH, Spencer at NASA) have persisted in the skeptical mind and discussion long after they've been updated (partly promulgated by such voices as Freds Singer and Seitz).
With Spencer finally saying it's time to move on, it's definitely time to move on -- just in time for the next IPCC preparation rounds, fortunately. Maybe by the end of that process the tree-ring, hockey-stick dilemma will be tending toward convergence, too.
I am sceptical, but neither am I silly enough to stick my head in the sand. I am sceptical of our scepticism, sometimes I am cynical about it.
Most of us learn after a few years, or a few dozen years, that the cheap shots always come back to bite you. A good scientist is always wrong on occasion; the only way you can avoid the risk of being wrong is to avoid saying anything substantial at all. It's hard enough to admit one was wrong; it a lot harder when you have to apologize for the insults as well.
By the way, do you know if there's any truth to the allegation that TCS is funded by Exxon-Mobil?
The urban heat island is only one part of what I meant by surface modifications. It belies the true extent of it. Everything from replacing thatch roofs with more permanent ones, to paving of roads and areas around farm houses, to channelization and so many other things, are the set of things that are in question in my statement. See if you can think of all the things that have essentially been introduced for the first time, over the past 100 or 150 years. Even things people often don't think of, such as how we plow fields - the depth, the size of the furrows, etc. It's all changed. Etc ...
And this is only with regards to surface modifications. Then there are all those other things to look at. Who, if anyone, could ever account for them all let alone understand the true impacts of them all?
This is an enormously complex thing to model accurately, let alone measure accurately.
That's what I was thinking of. I hope that he and others who bad-mouthed Fu might consider appropriate actions. It's not for me to say what they should actually do.
By the way, do you know if there's any truth to the allegation that TCS is funded by Exxon-Mobil?
Hmmm... Global Warming Skeptics: A Primer
Check out the entries under Baliunas and Glassman. (Ebell and McKitrick warrant a glance, too.) This is indicative, but requires further corroboration to be definitive.
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