Only 1 Year Away From Amazon Disaster!

[Jez]

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Amazon rainforest 'could become a desert' (http://www.climateark.org/articles/reader.asp?linkid=58635)

Dying Forest: One Year to Save the Amazon (http://www.commondreams.org/headlines06/0723-03.htm)




The vast Amazon rainforest is on the brink of being turned into desert, with catastrophic consequences for the world's climate, alarming research suggests. And the process, which would be irreversible, could begin as early as next year.

Studies by the blue-chip Woods Hole Research Centre, carried out in Amazonia, have concluded that the forest cannot withstand more than two consecutive years of drought without breaking down.

...

The research carried out by the Massachusetts-based Woods Hole centre in Santarem on the Amazon river has taken even the scientists conducting it by surprise. When Dr Dan Nepstead started the experiment in 2002 by covering a chunk of rainforest the size of a football pitch with plastic panels to see how it would cope without rain he surrounded it with sophisticated sensors, expecting to record only minor changes.
The trees managed the first year of drought without difficulty. In the second year, they sunk their roots deeper to find moisture, but survived. But in year three, they started dying. Beginning with the tallest the trees started to come crashing down, exposing the forest floor to the drying sun.

By the end of the year the trees had released more than two-thirds of the carbon dioxide they have stored during their lives, helping to act as a break on global warming. Instead they began accelerating the climate change.

As we report today on pages 28 and 29, the Amazon now appears to be entering its second successive year of drought, raising the possibility that it could start dying next year. The immense forest contains 90 billion tons of carbon, enough in itself to increase the rate of global warming by 50 per cent.



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[Jez]

The above articles needs a correction added to them:

Amazonian drought (http://www.realclimate.org/index.php/archives/2006/08/amazonian-drought/)



There has been a flurry of recent commentary concerning Amazon drought - some of it good, some of it not so good. The good stuff has revolved around a recently-completed interesting field experiment that was run out of the Woods Hole Research Center (not to be confused with the Woods Hole Oceanographic Institution), where they have been examining rainforest responses to drought - basically by using a very large rainproof tent to divert precipitation at ground level (the trees don't get covered up). As one might expect, a rainforest without rain does not do well! But exactly what happens when and how the biosphere responds are poorly understood. This 6 year long field experiment may provide a lot of good new data on plant strategies for dealing with drought which will be used to improve the models and our understanding of the system.

The not-so-good part comes when this experiment is linked too directly to the ongoing drought in the southern Amazon. In the experiment, older tree mortality increased markedly after the third year of no rain at all (with around 1 in 10 trees dying). Since parts of the Amazon are now entering a second year of drought (possibly related to a persistent northward excursion of the ITCZ), the assumption in the Independent story (with the headline 'One year to save the Amazon') was that trees will start dying forest-wide next year should the drought continue.

This is incorrect for a number of reasons. Firstly, drought conditions are not the same as no rain at all - the rainfall deficit in the middle of the Amazon is significant, but not close to 100%! Secondly, the rainfall deficits are quite regionally variable, so a forest-wide response is highly unlikely. Also, the trees won't all die in just one more year and could recover, depending on yearly variation in climate.


* Please note, the above quote leaves out the hyperlinks to lots of additional info which are embedded in the original article, and the article also contains a lot of additional comment about REAL problems the Amazon is facing and relates it back to the research misinterpreted in the first two articles.

Also, the researchers involved had this to say regarding the first two articles in the post above:




Posted on behalf of Daniel Nepstad, senior scientist at the Woods Hole Research Center, and lead investigator on the forest drought experiment. (Via Elizabeth Braun, Director of Communications at the Center.) -


"On July 23, The Independent report on the recent findings of our forest drought experiment in the Amazon, in which we reduced rainfall inputs to a hectare of forest over a five-year period. This alarmist article involved no interview, and it contains many statements that I do not support.

To clarify, our results do not show that the rainforest 'could become a desert'. In the third paragraph, the piece implies that I support the position that drought in the Amazon will lead to drought that would spread to Britain, with the world spinning out of control, becoming uninhabitable. That is simply not true.

What our work does show is that the drought we imposed caused big trees to die more than small trees, which was a surprise. We also know that the amounts of carbon that may be going to the atmosphere following Amazon droughts are probably big enough to accelerate global warming. Currently trends suggest that a big chunk of the Amazon forest will probably be displaced by fire-prone scrub vegetation; global warming will probably exacerbate this trend.

The challenges we are confronting and those that we will be faced with in the future are significant. The world's tropical rainforests will be changed in important ways by global warming. But public understanding of these processes is not served by evoking apocalyptic images. What is needed now is credible reporting and sound journalism so that the global community can act wisely."