How Scientists Found And Removed ‘False Warming’ In Satellite Data

Scientists in the Earth System Science Center (ESSC) at The University of Alabama in Huntsville ( UAH ) have calculated how much false warming NOAA-14 reported so the false warming could be removed from a long-term global atmospheric temperature record collected by MSU’s on satellites since mid-November 1978.



Weather Satellite Wanders Through Time, Space, Causing Stray Warming to Contaminate Data

In the late 1990s, the NOAA-14 weather satellite went wandering through time and space, apparently changing the record of Earth’s climate as it went.

Designed for an orbit synchronized with the sun, NOAA-14’s orbit from pole to pole was supposed to cross the equator at 1:30 p.m. on the sunlit side of the globe and at 1:30 a.m. on the dark side, 14 times each day. One of the instruments it carried was a microwave sounding unit (MSU), which looked down at the world and collected data on temperatures in Earth’s atmosphere and how those temperatures changed through time.

By the time NOAA-14 was finishing its useful life in 2005, however, it had strayed eastward from its intended orbit until it was crossing the equator not at 1:30 but at about 8:00. That pushed its early afternoon passage until after dark and its middle of the night measurements until well after dawn.

Because local temperatures typically change between 1:30 and 8:00, this introduced spurious temperature changes that had to be calculated and removed from long-term temperature datasets that use data from satellite instruments.

The drift also changed the satellite’s orientation relative to the sun, so that instead of instruments being shielded from sunlight in a consistent way, the sun’s rays peaked into unshielded and open crevices and other places where intense sunlight could influence the sensors. It warmed the MSU, which caused it to look at the atmosphere’s mid-troposphere (from the surface up to about 40,000 feet) as very slightly warmer than it actually was relative to its initial 1:30 crossing time.

Using data from weather satellites that stayed closer to home than NOAA-14, scientists in the Earth System Science Center (ESSC) at The University of Alabama in Huntsville (UAH) have calculated how much false warming NOAA-14 reported so the false warming could be removed from a long-term global atmospheric temperature record collected by MSU’s on satellites since mid-November 1978.

Details of that research have been published in the International Journal of Remote Sensing, and are available online at: https://www.tandfonline.com/doi/full/10.1080/01431161.2018.1444293

The wandering satellite became an issue when Dr. John Christy, director of UAH’s ESSC and lead author of the study, and Dr. Roy Spencer, an ESSC principal research scientist, were updating and revising UAH’s satellite-based global temperature dataset. (Version 6.0 was completed in 2016.) While they knew NOAA-14 had strayed from its path, a closer look showed the warming reported by the MSU on NOAA-14 was out of kilter with temperature data collected by instruments on other NOAA satellites. This seemed to be especially true in the tropical mid-troposphere.