Climate change in a nutshell

Economic indices like the Dow Jones are extremely powerful communications tools. The single number, distilled from perhaps hundreds of sources, combines a wealth of underlying information. The underlying data are essential to professionals in the field, but they are an unnecessary distraction to most others. The media stops at the index, only delving deeper when the markets crash or soar: most people are not interested in the detail.

Economic theorists argue how inaccurate these economic indices are for predicting economic trends, but nevertheless the press, the public, policymakers and economists follow them daily. They are easy to digest, and give a simple thumbs up/thumbs down assessment of economic trends.

The idea came about when several IGBP scientists, including Steven Running, former IGBP director Kevin Noone, Kathy Hibbard, Mark Stafford Smith, IGBP executive director Sybil Seitzinger, Peter Cox, Suzi Kerr and Pierre Friedlingsten, realised that the way various global datasets are reported throughout the year is confusing. It is uncoordinated, there is a variety of unfamiliar units, and natural variability sometimes masks a trend. The press and public are not clear about the scale of the changes scientists are witnessing. The index is a response to these concerns.

Why those four metrics? Steven Running from the University of Montana says, "The iconic Mauna Loa atmospheric CO2 concentration was obvious. Global air temperature is already widely reported at the end of each calendar year, so that was a logical choice too.

In the future, other variables could be added. "We did not identify any good land surface variable, because no good standard exists," says Running. "But some day we may have annual albedo or land-cover change."