Friday, June 27, 2008

{News} 071018 Rough Weather

Rough Weather

The Indian monsoon cycles are more vulnerable to climate change than previously thought, a new study shows. From eastern Africa to Australia, this may mean drought in some areas and more flooding in others.

Rebecca Hall
Newsweek Web Exclusive
Updated: 12:00 PM ET Oct 18, 2007

The Indian monsoon has always been a matter of intense interest to farmers on the subcontinent because it brings the summer rains, which account for 80 percent of annual rainfall. The phenomenon also drives weather patterns for a vast region that stretches from eastern Africa to Indonesia. Now scientists have found that global warming may have a much bigger impact on this key driver of Asian weather than previously thought. In a paper published today in the journal Science, researchers have now found that the climate system in the entire region is tightly linked to water temperatures in the Indian Ocean. This means that as global temperatures rise, Asia will undergo an upheaval in climate patterns, causing chronic droughts in some places and increased flooding in others. The key mechanism behind this change is the so-called Indian Ocean Dipole (IOD)—an annual event in which warm and cold water change places in the Indian Ocean, causing an east-west flip in wind direction, triggering the monsoons.

NEWSWEEK’s Rebecca Hall spoke by phone with Nerilie J. Abram, a climate scientist at the British Antarctic Survey in Cambridge, England, who led the research team from the Australian National University about the implications. Excerpts:

NEWSWEEK: What exactly is the Indian Ocean Dipole?

Nerilie J. Abram: The easiest way to think of it is the Indian Ocean’s equivalent of El Niño. It has a dramatic impact on the climate around the Indian Ocean but also has the potential to impact places further a field, as well. When the temperature changes its direction, the eastern Indian Ocean, normally the warmest side, becomes cold, and the western Indian Ocean becomes warm. That flip also means that the wind direction changes. Essentially, it is a reversal of the temperature gradient and wind direction.

Your research focused on coral. What does that have to do with monsoons in Asia?

Corals contain an amazing record of past climate. As corals grow they gain a band each year, kind of like how a tree has a ring for every year that it grows. We looked at that in great detail and measured the chemistry of the coral skeleton. This gave us a record for the ocean temperature that the coral was growing in. Additionally, it provided a measure of how much rainfall was being received. We were able to look at the temperature and the rainfall signals together in great detail, almost up to a weekly resolution. We can do this on corals that are currently living in the reef as well as fossil corals that provide snapshots in time of what the climate was like, at a weekly resolution, 6,000 years ago.

What is so interesting about 6,000 years ago?

We wanted to look at how the Indian Ocean Dipole operated about 6,000 years ago because we know that the Asian monsoon was much stronger then than it is currently. That might be partly analogous to the changes we are going to see in the future, because the monsoon is increasing, and that increase is predicted to continue because of global warming in the coming century. We wanted to determine if there were differences in the IOD from what we see now and what was recorded in the corals 6,000 years ago.

What did you find?

It has been known for a while that monsoons are going to increase and instrumental records are supporting this. The immediate implication is that the areas that receive monsoon rainfall will become wetter in the future. But our research also shows that it will have knock-on effects [a domino effect] in other parts of the climate system. As the Asian monsoon increases, it will produce greater and more widespread climate events than what we have previously imagined. For example, an IOD event will have a very dramatic effect on the countries surrounding the Indian Ocean. Indonesia will suffer massive droughts and wild fires. The drought will also extend into parts of Australia, and there will be flooding in eastern Africa.

How is this likely to affect the region?

When we looked at the timing of the droughts that happened 6,000 years ago, they had shifted to a different time of the year. So evidence of a strong cooling in the eastern Indian Ocean had a very strong drought to go with it. As a result of the shift, the maximum drought occurred in the month when the region would normally receive the most rainfall. You can imagine that as the Asian monsoon strengthens, we may get a similar shift in the timing of the droughts. This could have major implications for agriculture in this area. How farmers deal with the IOD now may not be the same way they will need to in the future. And the actual impact it has on their lives may become more severe if a drought cuts into what should be their peak rainfall period.

Is this a result of increasing global warming?

IOD is a natural phenomenon, and through the work we have done on the corals we can see that IOD events have happened naturally, going back at least 6,000 years but probably much longer. Like El Niño and monsoons, they are natural features of the climate, but we are trying to understand how it will change as a result of global warming.

Will your examination of the past assist others in predicting future weather patterns?

By looking at the past, we tried to get some more information about how these different tropical climate systems affect each other. Knowing that one part is changing, we can see how that might have a knock-on effect and influence another part of the climate system. The team is continuing to research the IOD because there is still a lot to learn. They are working in other parts of Indonesia to really start piecing together how the El Niño southern oscillation, as well as monsoons, fit into the whole story. We want to understand how those climatic impacts might change as global warming changes our climate.

Do IOD events become more severe when combined with El Niño?

The research into the IOD is still very much in its infancy, as it was only discovered in 1999. Monsoons and El Niño have benefited from many decades of research so we know a lot more about how they operate. El Niño has repercussions all around the world. It affects climate from Antarctica to Europe. One thing we do know is that if we have an El Niño event at the same time as an IOD event, the IOD acts to accentuate the climate features of El Niño. When they coincide, we end up with much stronger climate features than what we would ordinarily expect. This is adding a new piece to the puzzle that we didn’t know before.


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