IPCC is right: Amazon still at risk from drought, global warming

It’s been difficult to avoid the coverage in the media about the holes being poked in the 2007 report by the Intergovernmental Panel on Climate Change (IPCC).  But the latest attack, this one on the part of the report that says drought can be very damaging to the Amazon forest, gets it blatantly wrong.

The Amazon forest, the largest remaining tropical forest in the world and home to enormous biological and cultural diversity, stores about 100 billion tons of carbon.  In recent decades, the Amazon has become a major source of greenhouse gas emissions, as clearing forest for agriculture and cattle ranching have increased. Globally, emissions from deforestation now account for about 15% of total global emissions annually — more than all emissions from transportation worldwide — and between 2000 and 2005, 60% of the deforestation in the world happened in the Amazon.

Since the mid-1990s, scientists have observed that in dry years, particularly El Niño years, forest regions that were always too moist to burn have been catching fire, killing trees and increasing carbon emissions . Most climate change models predict that unless global greenhouse gas emissions are substantially reduced in coming years, forest in a large part of the southern and eastern Amazon risks large-scale dieback, releasing large amounts of carbon to the atmosphere and replacing the forest with savanna.

A new study lead by the World Bank, which includes experts from five international modeling groups and is independently reviewed by a blue-ribbon panel of international scientists, confirms these results.  The group looked at the effects of climate change, deforestation, and fires under different global emissions trajectories and found that if fossil fuels remain predominant in the global energy matrix, and deforestation attains 20% of the Amazon biome (it’s currently at 17%), 40% of the rainforest would be lost by 2025. And by 2100, climate change alone would reduce the Amazon forest by two-thirds.  In other words, the Amazon appears to be approaching a tipping point, after which large part of the ecosystem could collapse.

People I talk to who live in the Amazon forest, like rubber tapper leader Manoel Cunha and indigenous Chief Almir Surui, say they are already seeing the effects of climate change. Important forest species no longer flower or give fruit in the same season they previously did, droughts bring out-of-control forest fires, and rains fall out of season.  They are worried about the future of the forests they depend on for their livelihoods.

It is then, in this light, stunningly poor judgment that Boston University issued a sensationalistic press release misrepresenting a recent scientific article by BU scientists Samanta et al. in Geophysical Research Letters as discrediting an IPCC statement on the Amazon and climate change.

In the latest issue of Geophysical Research Letters, Samanta et al, used satellite data to check earlier findings that the Amazon got greener during the 2005 drought, rather than browner, as was expected.  They found that those previous results could not be replicated using an improved data set and that the Amazon in 2005 was neither greener nor browner than in non-drought years, so the previous results were incorrect.  The article’s conclusion – that the old study didn’t really show that the Amazon is more resistant to drought than people thought is actually a solid contribution to the remote sensing literature on forest carbon cycles.

It’s not clear how we got from here to the conclusion reported in the press and across the blogosphere that the study shows that the IPCC was wrong — but it wasn’t by using logic or science. Boston University’s recent press release titled “New study debunks myths about Amazon rain forests”, claims that Samanta et al.’s article disproves the IPCC’s affirmation that large part of the Amazon is drought sensitive.  But the article does nothing of the kind.

The article does not address any of the field surveys on the effects of drought that found greatly increased tree mortality, or large-scale rainfall exclusion experiments showing the same effects, or any of the modeling results. It does not consider that what happened in a single drought year may be much less important than what could happen with increasingly frequent droughts. It does not raise the mutually reinforcing effects of climate change, reduced rainfall, deforestation and fires. It does show that one series of data from one, mid-resolution satellite sensor, didn’t detect any measurable difference in the spectral signature of Amazon trees during one drought year.

One positive that has come out of the press release’s drastic mischaracterization of Semanta et al.’s article and corresponding news coverage is the quality conversations incited about the findings in the IPCC report.  I’ll conclude with a portion of a statement yesterday by 19 leading scientists who conduct research on Amazon forests, climate, and/ or fire released, which called the BU press release “misleading and inaccurate”.

There are multiple, consistent lines of evidence from ground-based studies published in the peer-reviewed literature that Amazon forests are, indeed, very susceptible to drought stress… [and] the main conclusion of the IPCC statement – that Amazonian forests are very susceptible to reductions in rainfall – remains our best understanding of the data available at the time of the IPCC report and also today.

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  • By sell on February 19, 2015 at 7:03 am


    IPCC is right: Amazon still at risk from drought, global warming | EDF Talks Global Climate

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