Global Temperature? Which Global Temperature?

When you talk about a "global average temperature," do you know what you are really talking about? It is not as easy as you might think.

The global average temperature exists as a theoretical concept. If we were able to place a large number of sensors around the world at regular spacings, we would be able to establish a meaningful estimate of the instantaneous average, which could then in turn be averaged over a year to produce a number that is a reasonable representation of the thermal state of the surface of the planet. Unfortunately, such a ground station network does not exist. Not only are the existing sensors poorly distributed, many are placed in thermally atypical sites such as cities and airports, others are in primitive rural areas where they are poorly maintained. Ironically though, it is over the oceans that the most discrepant surface measurements occur. Thus surface weather stations provide a very poor basis for determining average global temperature.

Fortunately there is an alternative, which is satellite surveillance. Microwave radiation from oxygen in the atmosphere is temperature dependent and therefore provides a convenient remote thermometer. Because the satellite orbit is continuously scanning the Earth’s surface like a television raster, it is equivalent to a very large number of well-distributed thermometers. As a result it produces a credible estimate of a global average temperature. The results cross calibrate well with data collected by balloons.

Less fortunately, the satellite record is relatively short, as the technology has not been around for very long. It shows a slight cooling trend, but all finite data sets show trends that are not necessarily properties of the parent distribution. All the satellite data tell us at the moment is that there are no dramatic changes of temperature occurring.

Numberwatch

Climate scientist Roger Pielke believes the only credible way to measure the heat content of the Earth, is by following the ocean heat content. Other than the sun, the oceans appear to be the clear driver of Earth's climate, due to their ability to hold and release large amounts of solar energy.

The huge problem of determining global mean temperature via ground surface stations is apparent when none of the large climate organisations can agree on rankings of "warmest recent years."

Here's what three of the world's leading agencies monitoring climate change say.

NASA's Goddard Institute for Space Studies, headed by James Hansen who is an advisor to Al Gore, says 2007 was the second warmest year on record.

Meanwhile, the U.S. National Oceanic and Atmospheric Administration says it was the fifth warmest.

And Britain's Meteorological Office (the MET), which does its analysis in conjunction with the University of East Anglia, and which at the start of the year predicted 2007 would likely be the warmest on record, says it was the seventh warmest.

TorontoSun via Tom Nelson

Since the US surface station network is the best in the world--and is a bloody mess--we should not base our futures upon projections that rest upon surface temperature readings. What is left? Satellite measurements--a distinct improvement but still imperfect--and ocean heat content estimates.

It may take several decades to upgrade temperature surface stations in the developed world. The undeveloped world may take centuries. So, clearly, while going about that difficult and time-consuming task, we should also look to satellite temperature and ocean heat readings. In other words, we need data--lots of data. The IPCC has a lot of "guesses" and projections based upon worthless ground temperature data combined with difficult to interpret "proxies" of past temperatures. That is not good enough to overturn the economies of the world. We need more, and better, data.

More on global temperature here.

More on lack of warming here.