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The UAH Global Temperature Dataset at 30 Years: A Look Back at the Early Days

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Roy W Spencer

Today (Monday, March 30) is the 30th anniversary of our publication in Science describing the first satellite-based dataset for climate monitoring.

Roy Spencer and John Christy

While much has happened in the last 30 years, I thought it might be interesting for people to know what led up to the dataset’s development, and some of the politics and behind-the-scenes happenings in the early days. What follows is in approximate chronological order, and is admittedly from my own perspective. John Christy might have somewhat different recollections of these events.

Some of what follows might surprise you, some of it is humorous, and I also wanted to give credit to some of the other players. Without their help, influence, and foresight, the satellite temperature dataset might never have been developed.

Spencer & Christy Backgrounds

In the late 1980s John Christy and I were contractors at NASA/MSFC in Huntsville, AL, working in the Atmospheric Sciences Division where NASA managers and researchers were trying to expand beyond their original mission, which was weather support for Space Shuttle launches. NASA/MSFC manager Gregory S. Wilson was a central figure in our hiring and encouragement of our work.

I came from the University of Wisconsin-Madison with a Ph.D. in Meteorology, specializing in the energetics of African easterly waves (the precursors of most Atlantic hurricanes). I then did post-doc work there in the satellite remote sensing of precipitation using microwave radiometers. John Christy received his Ph.D. in Atmospheric Science from the University of Illinois where he did his research on the global surface atmospheric pressure field. John had experience in analyzing global datasets for climate research, and was hired to assist Pete Robertson (NASA) to assist in data analysis. I was hired to develop new microwave satellite remote sensing projects for the Space Shuttle and the Space Station.

James Hansen’s Congressional Testimony, and Our First Data Processing

In 1988, NASA’s James Hansen testified for then-Senator Al Gore, Jr., testimony which more than any single event thrust global warming into the collective consciousness of society. We were at a NASA meeting in New Hampshire. As I recall, UAH’s Dick McNider on the plane ride up had just read a draft of a paper by Kevin Trenberth given to him by John Christy (who had been a Trenberth student) that discussed many issues with the sparse surface temperature data for detecting climate change.

During lunch Dick asked, given all the issues with the lack of global coverage and siting issues with surface data sets discussed by Trenberth, if there wasn’t satellite data that could be used to investigate Hansen’s global claims? NASA HQ manager James Dodge was there and expressed immediate interest in funding such a research project.

I said, yes, such data existed from the NOAA/NASA/JPL Microwave Sounding Unit (MSU) instruments, but it would be difficult to access approximately 10 years of global data. Note that this was before there was routine internet access to large digital datasets, and ordering data from the government had a very large price tag. No one purchased many years of global data; it came on computer 6250 bpi computer tapes each containing approximately 100 MB of data, and computers then were pretty slow. The data we wanted was from NOAA satellites, and NOAA would reuse these large (10.5 inch) IBM tapes rather than to keep the old data tapes around using up storage space.

It turns out that Roy Jenne who worked data systems at the NSF’s National Center for Atmospheric Research (NCAR) in Boulder had years before taken it upon himself to archive the old NOAA satellite data before it was lost altogether. He kept the data on a “mass storage system” (very large and inefficient by today’s standards) and I believe it was Greg Wilson who made the connection to gain us access to those data.

We obtained somewhat less than 10 years of data from NCAR, and I decided how to best calibrate it and average it into a more manageable space/time resolution. I had frequent contact with JPL engineers who built the MSU instruments, Fred Soltis in particular, who along with Norman Grody at NOAA provided me with calibration data for the MSU instruments flying on different satellites.

We enlisted John Christy to analyze those data since he brought considerable experience with diagnosing global datasets for climate purposes. One of the first things John discovered was from comparing global averages from different satellites in different orbits: They gave surprisingly similar answers in terms of year-to-year temperature variability. This was quite unexpected and demonstrated that the MSU instruments had high calibration stability, at least over a few years. It also demonstrated that NOAA’s practice of adjusting satellite data with radiosondes (weather balloons) was backwards: the differences others had seen between the two systems were due to poor spatial sampling by the radiosondes, not due to changes in the satellite calibration stability.

In addition to the critical historical data archived by Roy Jenne at NCAR, we would some of the more recent satellite data that was kept at NOAA. We didn’t have quite ten years of data, and an editor at Science magazine wanted ten full years of data before they would publish our first findings. We were able to order more data from NOAA to get the first 10 years’ worth (1979 through 1988), and Science accepted our paper.

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