Tag Archives: Satellite Data

About That Satellite Data

Last December, the United States Senate subcommittee on Space, Science, and Competitiveness, headed by Ted Cruz, held a hearing to which they invited a gaggle of climate change deniers and one good guy to testify about how the science on climate change is all wrong. I wrote about it here. The strangest aspect of this hearing was probably shock jock Mark Steyn’s use of the venue to argue his case in a civil law suit pertaining to his apparently libelous behavior. But there was another feature of this hearing worth noting. Both the deniers, in particular John Christy, and Senator Cruz focused on a set of data that they construed to indicated showed that global warming is not really happening.

The oceans are warming significantly. The Earth’s surface, as measured by thermometers as well as direct and indirect measurements of the sea surface, is warming significantly. The only people who doubt this are those who are either very badly misinformed or politically or financially motivated to deny reality.

But among the data are satellite based measurements of the troposphere. These data also show warming if properly analyzed, but some forms of these data can be used to make a graph that might give the impression that the warming we clearly see is not happening, or at least, not happening much.

So what is going on here? Are these satellite data telling the Real Truth, contrary to what all the other data show, or is this just a bad data set, or are these data being abused by contrarians?

Most of the satellite data in question come from a set of birds that are deployed for use in weather prediction, but secondarily measure the temperature of the Troposphere. They have sensors that collect microwave energy emitted by Oxygen molecules to estimate temperature. This technique has certain advantages and certain disadvantages, and is fairly easy to deploy.

How one goes from these microwave signals to a temperature measurement is actually very complicated. This has been further complicated by the failure of some of the instruments, and the fact that over time the satellites, in a polar orbit, lose altitude over time, which changes how the readings must be calibrated. Also, the satellites are supposed to pass over the Earth at nearly noon and nearly midnight (on opposite sides of the planet) as the Earth rotates beneath. But this synchronization goes off over a period of time as well.

And that is the simple version.

There have been many studies of these data, and attempts to adjust for all of the problems in this methodology. The experts do not all agree on how to correct the data. There are two approaches commonly used to produce potentially usable data (known as RSS and UAH) and each has advantages and disadvantages.

Skeptical Science has a set of three discussions, couched in less or more technical terms, of how this all works. If this is of interest to you, check it out.

Tamino, at Open Mind, addressed Ted Cruz’s misuse of the satellite data and concludes,

When Ted Cruz said that both satellites and balloon data fail to show warming, he was just plain wrong. When he said these data sets were the best evidence of whether warming is occurring, he was just plain wrong. Together, those two claims make up point number 4 of the 7 things he called “facts” — but he was wrong about their being facts. They’re just claims, claims which are just plain wrong.

Ted Cruz also didn’t seem able to keep straight how many of his so-called “facts” he listed. There were 7, but he repeatedly referred to 8. I guess when it comes to counting anywhere near as high as 10, Ted Cruz is again likely to be just plain wrong.