SYDNEY: The largest study of its kind reveals that global warming is already having a massive effect on life across the planet – greater even than habitat loss and deforestation.

The study, which analysed nearly 30,000 data sets stretching back to 1970, suggests that warnings spelt out last year by the U.N. underestimated the impact of the problem.

Significant changes

The data set covered phenomena as varied as the earlier leafing of trees and plants; the movement of species to higher latitudes and altitudes in the northern hemisphere in response to warmer weather; the shrinkage of glaciers and melting of permafrost; and changes of bird migrations in Europe, North America and Australia.

The study concludes that "significant changes" are already occurring among natural systems on all continents, with the exception of Antarctica, and in most oceans.

Published today in the U.K. journal Nature, it goes beyond the scope of the landmark report issued by the U.N.'s Intergovernmental Panel on Climate Change (IPCC) in February 2007.

In that document, the IPCC said man-made global warming was "likely" – within a probability of 66 to 90 per cent – to have had a "discernible" effect on many physical and biological systems.

The new study is authored by many of the experts who wrote the so-called Working Group I report, which was the first of a trio of major assessments released last year by the IPCC. Its approach widens the net of data for making a fresh analysis.

"Remarkable concordance"

"Humans are influencing climate through increasing greenhouse gas emissions," said lead author Cynthia Rosenzweig of the NASA Goddard Institute for Space Studies and the Columbia Centre for Climate Systems Research in New York City, USA. "The warming world is causing impacts on physical and biological systems attributable at the global scale," she said.

This study provides "overwhelming" evidence for change in physical and biological systems, commented Barry Brook, director of the Research Institute for Climate Change and Sustainability at the University of Adelaide in Australia. These changes include those affecting the timing of breeding events, changes to species ranges and population declines.

"Around 90 per cent of all reasonably long-term observations [in the study] show changes consistent with global warming and associated effects," he said. "There is always considerable natural variability in response of individual species, physical process and so on. Therefore, this level of concordance is really quite remarkable."

The effect is all the more remarkable when you take into account the fact that there has only been 0.75 ºC of warming so far, said Brook, yet the expectation for this century is four to nine times that amount.

"These changes are only a minor portent of what is likely to come, especially if we continue on our carbon profligate pathway," he said.

Not just human impact on habitats

"People sometimes wonder if the warming reported by climate scientists perhaps just reflects cities growing bigger, or changes in the way we measure temperature," noted Neville Nicolls who studies climate impacts at Monash University in Melbourne.

"[But] Rosenzweig and her colleagues used tens of thousands of time series of phenomena such as the timing of flowering or egg laying to test this. Most of their data were from well outside cities, and used nothing other than natural phenomena to 'measure' temperatures," he said.

In an accompanying commentary, also published in Nature, climatologists Francis Zwiers of Environment Canada in Toronto and Gabriele Hegerl of the University of Edinburgh in Scotland picked over the big dispute as to whether climate impacts could be pinned on human interference.

They placed a question mark over the 38-year period analysed by Rosenzweig's team. Evidence stretching back far longer than a few decades is needed to get a solid perspective, they said. But, they added, these criticisms are outweighed by "the sheer number" of impacts on species and ecosystems the study cites.