Abrupt Climate Change Could Drag Monsoon Over the Ocean, Decreasing Vegetation Growth

monsoon clouds photo

photo: Ken Bosma via flickr

About three months ago we learned of new research from Purdue University showing that climate change is likely shift the onset of the monsoon 10-15 days later in many parts of South Asia and in many places decrease its intensity. Now research coming out of Oregon State University shows that abrupt climate changes in the past have already played havoc with the monsoon:The research, published in today's edition of Science, shows that in the past the monsoon shifted so far to the south that most of its precipitation fell over the oceans, resulting in serious drops in vegetation growth on land.

Ice Core Samples Tell the Story
The scientists, which in addition to the OSU researchers included members of the Scripps Institution of Oceanography and The Desert Research Institute, examined oxygen isotopes in ice cores and previously published data on ancient stalagmites. The oxygen isotopes were examined to gauge changes in vegetation occurring over the past 100,000 years, with changes in vegetation being indicated by changes in the ration between different oxygen isotopes.

Ed Brook, professor of geosciences at OSU:

Changes of this type have been theorized in climate models, but we've never before had detailed and precise data showing such a widespread impact of abrupt climate change. We didn't really expect to find such large, fast environmental changes recorded by the whole atmosphere. The data are pretty hard to ignore.

Both the ice core data and the stalagmites in the caves gave us the same signal, of very dry conditions over broad areas at the same time. We believe the mechanism causing this was a shift in monsoon patterns, more rain falling over the ocean instead of the land. That resulted in much lower vegetation growth in the regions affected by these monsoons, in what is now India, Southeast Asia and parts of North Africa.

Oxygen levels and its isotopic composition in the atmosphere are pretty stable, it takes a major terrestrial change to affect it very much. These changes were huge. The drop in vegetation growth must have been dramatic.

The caveat in all this, the article says, is that past climatic data does perfectly predict future changes. However, this study does point to the fact that monsoon behavior is closely linked with climate change, and in the past abrupt climate changes have occurred in the span of decades.

More: Science (subscription or pay-per-article)

Monsoon, Climate Change
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