Climate Change & Tropospheric Temperature Trends - Part I: What do we know today and where is it taking us?PDF Version
A paper by me on the state of troposphere temperature trend research as of March 2005. Part I deals with the upper-air record and is mainly a Year 2005 update of the Year 2000 NRC reports linked above. Part II
, which is linked off of my Climate Change Skeptics page
, deals with the way this record has been used by industry and Far-Right special interests seeking to refute the evidence for anthropogenic climate change. In spring of 2005, shortly after this paper was released a basic math error (a misplaced minus sign) was discovered in the satellite-based datasets most frequently cited by these interests. When the error was corrected the trend differences between these datasets and those of climate models and other teams fell well within the range of statistical noise, and the whole conflict vanished. Since then this record has been abandoned by most skeptics as evidence against global warming, and with it over ten years worth of insistent claims that it is more reliable than other datasets. Yet even to this day, some Far-Right special interests still cite these records as "proof" that global warming isn't real.
Reconciling Observations of Global Temperature Change
The Year 2000 report from the National Research Council summarizes the state of knowledge regarding global radiosonde and satellite-based troposphere temperature trends microwave at the time it was published. This report was the starting point for many successive efforts to clarify the upper-air record and determine whether its discrepancies with surface temperature trends and climate models were spurious or real—an issue which has since been resolved as shown in other sources linked here.
Understanding Recent Atmospheric Temperature Trends and Reducing Uncertainties
(Draft White Paper prepared for the US Climate Change Science Program, Nov. 2002)
A Year 2002 Report from the U.S. Climate Change Program similar to the NRC Year 2000 report, but with updated information, including a discussion of the Remote Sensing Systems (RSS) Version 1.0 satellite retrieval.
Temperature Trends in the Lower Atmosphere: Steps for Understanding and Reconciling Differences - Final Report 1.1
(U.S. Climate Change Science Program, May 2005)
In 2000, after the release of the NRC report global temperature change, the U.S. Climate Change Science Program set out to investigate the discrepancies between surface and atmospheric temperatures as observed by satellites and radiosondes (weather balloons). The Program’s preliminary investigation and plans for further investigation were set forth in the draft white paper in the second link. This report, released in May of 2005 presents the USCCSP’s final results in which they demonstrate the agreement between surface and atmospheric temperature records and suggest agendas for further research. The first link is to a page that has links to the full contents of each section, as well as one to the complete report (9.2 mb download). The report's Executive Summary is available here
A Reanalysis of the MSU Channel 2 Tropospheric Temperature Record
(Mears et al. 2003.J. Climate, 16 (22))
This paper from Remote Sensing Systems (RSS) presents Version 1.0 of their MSU derived upper-air analysis and resulting troposphere and stratosphere temperature trends. RSS analysis products use different methods for processing these records than the University of Alabama, Huntsville (UAH) products that were in conflict with climate model predictions at the time this paper was published. Specifically, RSS relied on the unprocessed MSU datasets which view bulk brightness temperatures for mainly in the middle and upper troposphere (or the free trosposphere) while UAH relied on “synthetic channel” data that emphasized the lower troposphere by combining various side-looking views of the MSU detectors. RSS also use different methods for removal of noise from the data and combining the records of different satellites over time to produce a continuous trend. There are strengths and weaknesses to each approach and neither approach is clearly better than the other in all respects. The mainstream climate science community relies on both, but tends to favor this record over the UAH products because it agrees well with two more analyses that used analysis methods independent of its and UAH’s (Prabhakara et al, 2000; 1998 Geophys Res Lett), and because there is general agreement that RSS methods are less subject to noise of various kinds than their UAH counterparts. Climate skeptics have relied exclusively on the UAH products for their case because it yields the smallest warming trends of all available datasets.
UAH Channel 2 (T2) MSU Datasets
(MSU Channel 2: the Free Troposphere)
UAH Channel 4 (T4) MSU Datasets
(MSU Channel 4: the Lower Stratosphere)
UAH TLT MSU Datasets
(Lower Troposphere Synthetic Channel. The corrected Version 5.2 Datasets are here)
These papers present the two most recent (as of Jan. 2007) UAH MSU analysis products. The first presents Version D (2000) and the second, Version 5.0 (2003). Version 5.2 (May 2005) was the first dataset in which the erroneous diurnal drift for the NOAA-11 satellite had been corrected (see Mears & Wentz, 2005, linked below). The final links are to the UAH public data access server where their datasets can be downloaded and used. The datasets labeled “5.2” at the last link are those with the correct diurnal drift adjustments.
Global warming: Evidence from satellite observations
(Prabhakara et al. 2000. Global warming: Evidence from satellite observations, Geophys. Res. Lett., 27 (21), pp. 3517–3520)
The second of two MSU analysis products from a team lead by Prabhakara of NASA. This analysis is similar to the RSS products, except that their merge analysis assumed a constant temperature calibration (based on an onboard “hot target” at a known temperature). The UAH and RSS teams both derived corrections for each satellite in the series as part of their merge calculations. The trends in this paper agree well with the comparable RSS trends, but not with those of UAH Version D to which they are most comparable.
Global Warming Trend of Mean Tropospheric Temperature Observed by Satellites
Vinnikov, Y.V. & N.C. Grody. 2003. Science, 302 (5643)
The paper by Vinnikov & Grody presenting their MSU derived upper-air retrieval and analysis, which was based on a unique statistical method to merge the different satellite records. Vinnikov and Grody’s method is very different than that of the other teams. It is based on certain assumptions about daily, annual, and interannual cycles in atmospheric temperature that, if valid, will yield the most accurate and noise-free results of any of the extant analysis products. However, if these assumptions differ significantly from the actual temperature cycles they simulate, considerable error might result. This product yields the highest warming trends of the currently published MSU analyses, and has received less attention than the UAH and RSS products.
The Effect of Diurnal Correction on Satellite-Derived Lower Tropospheric Temperature
CA Mears and FJ Wentz. Science, published online 11 August 2005
This is the August 2005 paper first published online at Science Express (subscription required for full text) in which Carl Mears and Frank Wentz of RSS present their discovery that UAH MSU products had been applying corrections to the MSU data from the NOAA-11 satellite in the wrong direction, thereby introducing a spurious cooling into UAH analyses. When the error was corrected, beginning with UAH Version 5.1 (Christy et al, 2005) this record’s disagreement with extant climate model predictions of global warming all but vanished and with it the only potentially credible argument global warming skeptics ever had. The NOAA TIROS Series of satellites that carry the MSU packages are in polar orbits that are sun-synchronous (i.e.—in orbits that preserve their orbital plane with respect to the sun throughout the year so that they rise and set in the sky at the same time on any given day and location during their service lives). Imperfections in this sun/satellite synchronicity cause a drift in the satellite’s daily rising and setting times during its life that will appear to the sensor as a spurious warming or cooling depending on the direction (it’s usually much cooler at 6 AM than it is at noon!). This is referred to as diurnal drift. NOAA-11 had a comparatively large one—enough so that reversing the correction for it was enough to spuriously remove most of the warming that should have been present in UAH products.
Correcting the MSU Middle Tropospheric Temperature for Diurnal Drifts
Mears et al. 2002. Proceedings of the International Geophysics and Remote Sensing Symposium, Volume III, pp. 1839-1841
This 2002 paper from the RSS team describes the issues involved in correcting remotely sensed temperature data from satellites for diurnal drift (variations in the sun-synchronicity of polar orbits) and the methods used to correct their MSU datasets. The UAH team relies on a different method based on comparisons of the MSU sensors’ side-looking views—that is, at angles to the left and right of nadir (straight down) along its flight path.
Atmospheric science: Stratospheric cooling and the troposphere (reply)
Fu et al. 2004. Nature, 432, doi:10.1038/nature03210 Brief Communications. Dec. 2, 2004
Estimation of Tropospheric Temperature Trends from MSU Channels 2 and 4
Spencer et al. 2006. J. Atmos. Oc. Tech., 23, pp. 417-423
MSU sensors measure temperature by detecting the total amount of microwave radiation emitted by a layer of the atmosphere, the altitude and thickness of which depend on the frequency (wavelength) being measured. These measurements are taken on multiple channels, each of which looks at a different frequency and therefore a different “slice” of the atmosphere. The channel that is of most interest to global warming studies is Channel 2 which looks at a layer that covers most of the troposphere—where we expect the biggest global warming fingerprint. The stratosphere above it, which is measured by Channel 4, has long been known to be cooling (for other reasons). One problem that has beset these studies is that the atmospheric layer seen by Channel 2 dips a little ways into the lower stratosphere, making it a good, but not exact look at the troposphere. As such, it includes some unrelated stratosphere cooling into its look at the troposphere, making its numbers artificially small to some extent.
This paper from a team led by Qiang Fu of the University of Washington (in my home town of Seattle) describes a method whereby data from Channel 4 is used to estimate the size of this spurious stratosphere cooling in the Channel 2 measurements and correct for them. In doing so, they removed much of the disagreement between observed troposphere warming and that predicted by climate models. The study proved controversial not only because it gave results that were unpalatable to global warming skeptics, but because the UAH team and a few other researchers expressed concerns about whether the stratospheric impact on Channel 2 data was uniform enough spatially and temporally for such a correction to be made. In the second paper Fu’s team responds to its critics in this regard, and in the third Fu and Johanson (also of the UW) present an improved version of the analysis that supports the original conclusions with more data, granularity, and independent cross-checks. The last paper is from the UAH team and presents their critic of the method. Generally speaking, the UAH concerns about what has come to be called the “Fu Method” are theoretically valid, but of relatively little impact because the stratosphere is uniform enough with respect to tropospheric variability to allow it to be used.
Stable Long-Term Retrieval of Tropospheric Temperature Time Series from the Microwave Sounding Unit
Mears, CA and FJ Wentz. 2002. Proceedings of the International Geophysics and Remote Sensing Symposium, Volume III, pp. 1845-1847
Another paper from RSS summarizing their methods for merging the MSU records and removing noise from them. “Merging” is the term used to describe the process of creating a single continuous temperature record for the life of the program (which began in 1978) by combining the data from different satellites that were in service at different times and correcting their temperature sensor calibration offsets with respect to each other.
Effects of Orbital Decay on Satellite-Derived Lower Tropospheric Temperature Trends
FJ Wentz & M Schabel. 1998. Nature, 394, pp. 661-664
This 1998 paper from Frank Wentz and Matthias Schabel of RSS describes one source of error in the MSU record by which the decay of satellite orbit over the lifetime of a given MSU sensor’s record introduces a spurious cooling into its data. Subsequent to the publishing of this paper all extant MSU datasets have been corrected for it. UAH products that predate 1998 (their versions B and C) were not corrected for it, yet are still being cited by a few of the more stubborn global warming skeptics, one notable example being the unpublished paper that accompanied the Oregon Institute of Science & Medicine’s 1998 petition project
. Even to this day that petition and its paper are being cited as proof that “17,000 scientists and engineers” (or in some references, 15,000) dispute global warming. The error is particularly egregious because the paper in which UAH Version C was published (Christy & Lobl, 1998, J. Climate
) specifically mentions this error and points out that their data had not been corrected for it because the discovery had been made after the paper’s galley proofs had gone back to final press (subsequent UAH products were).
NOAA KLM Orbiter User's Guide: 2000
NOAA-K through NOAA-M with NOAA-N Supplement
1998 User's Guide Sect. 4.3 (MSU)
MSU Package, TIROS-N through NOAA-14
2000 KLM User's Guide, Section 3.4 (AMSU-B)
AMSU-B Package, NOAA-K through NOAA-M
These are the NOAA User’s Guides for NOAA’s Polar Orbiting Environmental Satellite (POES) series of spacecraft and their onboard systems, including the Microwave Sounding Unit (MSU) packages that are used to gather atmospheric temperature data. The 1998 Guide covers all satellites in the NOAA POES Series up to 1998 from TIROS-N (launched on Oct. 31, 1978 with the first generation MSU package) through NOAA-14 (launched in December of 1994). The second is for the next-generation NOAA KLM Series of spacecraft, beginning with NOAA-K (launched in December of 1994). These satellites carry the Advanced MSU, or AMSU, which has been separated into two packages with separate tasks: AMSU-A and AMSU-B. These have improved sensitivity, better noise reduction, and an expanded number of views and view angles per cross-track sweep of the detectors. All MSU based analysis products account for the differences in their temperature trend analyses. The last three links are to the subsections of the corresponding User’s Guide covering the MSU or AMSU packages used in both satellite series.