24 April 2012

Winds and chaos

Yesterday, in a kitchen in Washington D.C. :
  - Michele : “My Dear, do you know that last March has been the hottest month of March in the U.S. since 1895 ?! I do not like these heat waves. Can’t the scientists predict them?”
  - Barack : “Oh Dear, climate is complicated, it is very difficult to predict. And concerning the heat waves, unfortunately global warming will mean more of them!…”

Chaos in the air 

For the scientists dealing with climate change, the forecast of the climate in the next decades is a key item. Models build these predictions. They show trends however no one can declare they are perfectly accurate. Why? Because the climate is an extremely complex system and humans have been studying it for only few decades.

We met Christophe in Nouméa 
on the 16th of April. In the past 
Christophe worked in the 
United States and Ivory Coast.
“The weather here in the Pacific Ocean is even less predictable than in the Atlantic Ocean for instance”, says Christopke Menkes. We met Christophe Menkes in Nouméa, New Caledonia, at the Institute of Research for Development (Institut de Recherche pour le Développement, IRD) which is a French governmental organization dedicated to research, outside of metropolitan France. Christophe is an expert in oceanology and focuses especially on cyclones, environmental impacts on tuna, and climate effects on Dengue spreading.

Christophe explains : “When dealing with climate predictions, there is a part of variability that cannot be reduced. The chaos theory explains this : many conditions influence the climate and very slight changes of these conditions can totally modify the consequences.” Maybe you have heard about the butterfly effect? 'A butterfly wing flapping in Japan might be the origin of a cyclone in the United States!'

From winds to cyclones 

Christophe adds : “For instance, about cyclones, specific winds of West Africa are always at the origin of the Atlantic cyclones. It is what we call a forcing input. In South West Pacific, the conditions are more complex and more random”.
The tropical cyclones, between 1945 and 2006 -
The area in South West Pacific where the cyclones are generated extends from the Solomon Islands to Tonga. New Caledonia is located in the middle of this cyclonic region.
“Concerning the cyclonic activity in the South West Pacific region, studies say that global warming will not necessarily mean an increase in numbers of cyclones. Regarding their intensity, only two studies have been published so far and they predict that the cyclones will be more intense in this region. The question should be more investigated to give solid conclusions”, says Christophe.

“Regarding the Central Pacific, things are clearer. The phenomenon El Niño has a direct impact on the generation of cyclones.” The El Niño episodes are defined as warmer than normal sea-surface temperatures in the tropical Pacific Ocean. “The more El Niño occurs, the more cyclones will emerge ; and the studies show that climate change is the origin of more and more periods of El Niño.”

Irene, Katrina, Rita… nice names which worry North East America

Concerning the Atlantic, there is observational evidence of an increase in intense tropical cyclone activity in the North Atlantic since about 1970. “In some cases natural variability of the climate can result in an extreme event being more intense on a long period. However in the North Atlantic the recent change is a consequence of human activity,” says Christophe.

The cyclone (or hurricane) Katrina of 2005 was one of the most destructive and expensive natural disaster in U.S. history. It claimed 1 800 lives and caused 134 billion dollars in damage (U.S. Global Change Research Program, 2009). We also remember that last year Irene forced New York City to stand still during some days and be partially evacuated. The Big Apple will probably experience these circumstances again in the future.

Land lost during 2005 Hurricanes - 
In 2005, in the United States, 560 km² of land and wetlands were lost to open water during hurricanes Rita and Katrina. The photos and maps show the Chandeleur Islands, east of New Orleans, before and after the 2005 hurricanes ; 85 percent of the islands’ above-water land mass was eliminated (U.S. Global Change Research Program, 2009).

At end of March, the Intergovernmental Panel on Climate Change (IPCC) published a special report about extreme events, called Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation. The report assesses the evidence that climate change has led to changes in climate extremes – cyclones, droughts, floods, heat waves - and the extent to which policies to avoid these prepare for, respond to and recover from the risks of disaster can reduce the impact of such events. Regarding cyclones, the conclusions are the following : “first, it is likely that the global frequency of tropical cyclones will either decrease or remain essentially unchanged. Second, average tropical cyclone maximum wind speed is likely to increase, although increases may not occur in all ocean basins.”

Presentation video of the special report by the IPCC. The report can be downloaded here.