The IGBP Climate Change Index debuts in Copenhagen

International Geosphere-Biosphere Programme: Some people still question whether Earth's climate is changing as rapidly and profoundly as the majority of climate scientists suggest. But, what if the complexity of the Earth's climate were distilled down to one number, in the same way that the Dow Jones Index condenses volumes of data into a single figure? What, then, would be the general trend?

The IGBP Climate-Change Index is a first attempt to do just that. It brings together key indicators of global change: carbon dioxide, temperature, sea level and sea ice. The index gives an annual snapshot of how the planet's complex systems - the ice, the oceans, the land surface and the atmosphere - are responding to the changing climate. The index rises steadily from 1980 - the earliest date the index has been calculated. The change is unequivocal, it is global, and, significantly, it is in one direction. The reason for concern becomes clear: in just 30 years we are witnessing major planetary-scale changes.

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

Why those four metrics? Professor 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.

"We needed an oceanic measure and chose sea-level rise because the impact is global and of high public interest. The fourth metric concerns the cryosphere. Growing concern about the rate of loss of summer sea-ice in the Arctic led us to choose this metric. This parameter broadly represents the Earth system and it is interesting the summer sea-ice extent is shrinking much faster than models predicted five, ten years ago," said Professor Running, a lead author on the Intergovernmental Panel on Climate Change Fourth Assessment Report.

In the future, other variables could be added. "We did not identify any good land surface variable, because no good standard exists," says Professor Running. "But some day we may have annual albedo or land-cover change." Each parameter is normalised between -100 and +100. Zero is no annual change. One hundred is the maximum-recorded annual change since 1980. The normalised parameters are averaged. This gives the index for the year. The value for each year is added to that of the previous year to show the cumulative effect of annual change.

Professor Running says, "Some of us thought we'd need a five-year rolling average to help dampen fluctuations and to elucidate core trends. But when we first produced the index it was obvious this was unnecessary: the index highlights the trend extremely effectively."…