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May 16, 2008

Study Shows Human-Caused Climate Change
Responsible for Global Impacts
First-ever survey of data shows human activity
linked to changes in diverse physical and biological systems

A vast array of physical and biological systems across the earth are being affected by warming temperatures caused by human activity, says a new Columbia study. These impacts include earlier leafing of trees and plants over many regions; movements of species to higher latitudes and altitudes in the Northern Hemisphere; changes in bird migrations in Europe, North America and Australia; and shifting of the oceans’ plankton and fish from cold- to warm-adapted communities. Based on an analysis of aggregated data, this study is the first to link observed global changes in diverse systems to human-caused, or anthropogenic, climate change. The study appears in the May 15 issue of the leading scientific journal Nature.

Retreat of the Chacaltaya Glacier, Bolivia: Until 2004 the Chacaltaya Glacier hosted the only ski area in Bolivia, which at 5,300 meters was also
the world's highest ski run. Chacaltaya Glacier has now melted almost entirely due to warming and
skiing is no longer possible. The ski lift, indicated with a red line, had a length of about 800 m in 1940
and about 600 m in 1996. The red cross shows the position of the ski hut, which did not exist in 1940.
The original location of the ski lift in 1940 is indicated with a black segmented line in subsequent
years. Sources: IPCC Working Group II Fourth Assessment Report 2007; 1940 Servicio Aerofotográfico Nacional, Bolivia; 1982
Reinhardt & Jordan; 1996, 2005 Bernard Francou
Retreat of the Chacaltaya Glacier, Bolivia 1940-2005
(Click image above for larger photo)
Sources: IPCC Working Group II Fourth Assessment
Report 2007; 1940 Servicio Aerofotográfico Nacional, Bolivia;
1982 Reinhardt & Jordan; 1996, 2005 Bernard Francou

“Humans are influencing climate through increasing greenhouse gas emissions, and the warming world is causing impacts on physical and biological systems attributable at the global scale,” said lead author Cynthia Rosenzweig, a scientist at the NASA Goddard Institute for Space Studies and the Columbia Center for Climate Systems Research. Both are affiliates of The Earth Institute at Columbia University.

Rosenzweig and researchers from 10 institutions across the world analyzed data from published papers on 829 physical systems and some 28,800 plant and animal systems, stretching back to 1970. Their analysis reveals a picture of changes on continental scales; previous studies had looked mainly at single phenomena, or smaller areas. In physical systems, 95 percent of observed changes are consistent with warming trends. These include wastage of glaciers on all continents; melting permafrost; earlier spring river runoff; and warming of water bodies. The study also found that 90 percent of changes among living creatures inhabiting these systems are consistent with warming.

The researchers say it is unlikely that any force other than human-influenced global warming could be driving these changes; factors like deforestation or natural climate variations could not explain it. Their work builds upon the consensus of the Intergovernmental Panel on Climate Change, which in 2007 declared human-made climate warming “likely” to have discernible effects on biological and physical systems.

“It was a real challenge to separate the influence of human-caused temperature increases from natural climate variations or other confounding factors, such as land-use changes or pollution,” said coauthor David Karoly, a climate scientist at the University of Melbourne in Victoria, Australia. “This was possible only through the combined efforts of our multi-disciplinary team, which examined observed changes in many different systems around the globe, as well as global climate model simulations of temperature changes.”

The researchers’ findings show that patterns of change are strongest in North America, Asia and Europe—mainly because far more studies have been done there, said Rosenzweig. On the other continents, including South America, Australia and Africa, documentation of changes in physical and biological systems is sparse, even though there is good evidence of human-influenced warming itself. The authors say that there is an urgent need to study these environmental systems, especially in tropical and subtropical areas.