Wednesday, March 24, 2010

More clarification for the IPCC

See Update March 29 below.

Simon Lewis of the University of Leeds tries once again to clarify his real views regarding the Amazon as reported by the Sunday Times.

Lewis said he was contacted by the Sunday Times before the article was published and told them the IPCC’s statement was “poorly written and bizarrely referenced, but basically correct”. He added that “there is a wealth of scientific evidence suggesting that the Amazon is vulnerable to reductions in rainfall”. He also sent the newspaper several scientific papers that supported the claim, but were not cited by that section of the IPCC report.


So the IPCC said "reduced rainfall could wipe out up to 40% of the Amazon rainforest," and Lewis says "the Amazon is vulnerable to reductions in rainfall." I would think the latter statement is obvious. Is there any actual evidence for the former statement? Richard North says there is no significant evidence to support the claim that drought such as in 2005 does little or no significant damage to the Amazon; on the other hand, there is a lot of uncertainty as to how much damage is done, and how long it lasts (how resilient the Amazon is). In the meantime, since 2005 there may have been more flooding than drought.

UPDATE: Bishop Hill is now on the case. ANOTHER UPDATE: Richard North again. Is there any kind of certainty as to how much rain a rainforest needs to avoid massive tree death? How much drought can be sustained, over how long a period of time, before there is massive tree death? That in fact even a modest decrease in rainfall, if it goes on long enough, could cause the destruction of 40% of the Amazon rain forest? Indeed, do experts agree as to whether climate change is likely to cause more rain or less rain in the Amazon? It seems by now that whichever happens, they will say they predicted it.

To no one's surprise by now, there is little certainty about any of this. Anyone can say that in some cases, rain forest has been turned into savannah by a lack of rain; the decrease in rainfall may not seem all that dramatic, but if it goes on long enough, it can have dramatic effects. But is there is any knowledge about where the tipping point is, either in amount of rain, duration of drought, or anything?

The most hilarious quote from Daniel Nepstad, who is one of Lewis's authorities although Lewis does not cite this particular piece:

One of the great ecological puzzles of the Amazon forests is their ability to withstand severe seasonal drought with no visible signs of drought stress.


So there is no trend today toward the Amazon disappearing because of drought--especially since there seems to have been massive rainfall and flooding since 2005. (I know, I know, they predicted it as long as it is somehow "extreme").

Maybe one observation to make is that contrary to what we are often told, the earth as a whole is not fragile--it is actually highly resilient. Bambi is fragile--he was born as a prey animal, with a big X on his chest, and he is certain to die young--compared to say a deer in a zoo. Human beings in a way are fragile, although we have adapted much better than deer to life in many different climates. Species have been wiped out--but far fewer have been wiped out by human action than you might think. Ecosystems change. But a variety of life forms have survived many changes, even what we would have to call truly catastrophic changes. Sometimes the diversity of life forms is greatly reduced, but then new life forms arise.

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