Don’t be swayed by recent blog posts claiming that the Amazon benefits from climate change.
Some of the world’s most eminent tropical forest scientists have debunked such posts, calling them uninformed and ridiculous.
The posts, published last month on The Telegraph and The Register by Tim Worstall, a Senior Fellow at London’s Adam Smith Institute, asserted that a new Nature study indicates that “climate change will mean new and larger tropical forests.”
“We’re told, endlessly, that climate change will mean the end of the Amazon, of the tropical forests, and the Earth will lose its lungs,” he wrote. “It appears that this is not wholly and completely true. Actually, an increase in CO2 in the atmosphere is likely to lead to the growth of huge, new, tropical forests.”
The paper in question looks specifically at the potential impacts of higher carbon dioxide levels on plant growth in the savannas of Africa.
It found that elevated CO2 levels may favor so-called C3 plants like trees over C4 plants like grasses, leading to more trees sprouting up across Africa’s grasslands and potentially more African woodlands.
Worstall extends the findings to argue that increased carbon levels will suddenly cause new rainforests to emerge worldwide.Photo: Rhett A. Butler.
“The major point of this paper is that far from climate change being a threat to the tropical forests, it looks as if it will be the cause of more of them growing,” he writes on The Register.
“Burning more fossil fuels therefore seems likely to grow several new Amazon style forests across Africa and Latin America,” he adds on The Telegraph’s finance blog.
But some of the world’s leading tropical forest experts took aim at Worstall’s logic, noting the limitations of the study as well as the other factors that are endangering rainforests.
“This is a typically uniformed piece by Tim Worstall. After confusing Amazon rainforests and African savannas, he implies that scientists only report on what he calls negatives, such as the impacts of extreme droughts on tropical forests, and not on what he calls positives, like carbon dioxide increasing plant growth. A simple call to a scientist working in the area could have pointed him to papers showing both things. Simpler still he could have read the newspaper website he writes for, where both drought and carbon dioxide impacts have been reported,” Simon Lewis, a tropical forest expert at the University of Leeds, told mongabay.com.Photo: Rhett A. Butler
Lewis, who led one of the most extensive studies of carbon uptake in tropical forests, explained that while there is evidence that more trees are growing across the drier parts of Africa, it doesn’t mean rainforests are poised to expand.
“Growth of new tropical forests depends on vegetation responses to multiple changes in the environment and complex feedbacks. Increasing carbon dioxide amounts in the atmosphere tends to increase tree growth, but higher air temperatures tends to reduce growth. Droughts and associated fires kill trees,” he said, adding that the new scientific paper that Wortall cites ignored the effects of drought, which would reduce tree growth.
“A common view within the scientific community is that at higher carbon dioxide concentrations, if businessPhoto: Rhett A. Butler
as usual emissions continue, eventually tropical trees will become saturated with carbon dioxide, and at much higher temperatures, photosynthesis may well decline, and there will be more fires and droughts which combined may reduce overall tree growth and increase tree deaths. This net impact is not a panacea for tropical forests. Even a rudimentary grasp of the scientific literature would show that Tim Wortall’s dramatic statement is a fairly wild extrapolation from a single scientific paper.”
Greg Asner, an ecologist with the Carnegie Institution who has done advanced assessment of the impact of droughts across the Amazon, agreed with Lewis.
“Worstall has taken a single study on a single component process (CO2 uptake) in a very different ecosystem and extrapolated it to a totally different biome encompassing all processes at a global scale, and then he proceeded to concoct an interpretation of that study that is inconsistent with what is happening at the large scale in the tropics,” he told mongabay.com.
“The real problem here is physiology, time and scale,” Asner continued. “Sure, you can feed someone more and more donuts and they might gain the weight, but cut off their water repeatedly, and gradually increase the temperature in the room, and those poor souls will keel over, just more dramatically with all those extra donuts ingested. That’s exactly what is happening with climate change in the humid tropics. Yes, the trees are getting more CO2 in the background, but in the foreground are these repeated droughts and constantly increasing nighttime temperatures that pull the vegetation back, and to the ground. We are still trying to assess the longer-term effects of the 2010 drought in the Western Amazon, but there’s no sign that the forests did ‘well’.”Photo: NASA
In fact, drought and other factors are triggering the opposite of the picture painted by Wortall, according to Eric Davidson, Executive Director and Senior Scientist at the Woods Hole Research Center in Massachusetts.
Earlier this year Davidson led a review of 100 studies looking at the effects of disturbance and climate change on the functioning of the Amazon Basin. It concluded that the combination of deforestation, forest degradation, and the effects of climate change are weakening the resilience of the Amazon ecosystem, potentially leading to loss of carbon storage and changes in rainfall patterns and river discharge. Among the changes was a shift from rainforest to savanna.
“As our review paper in Nature earlier this year describes, the transition forest on the southern flank of the Amazon is showing a transition from forest to savanna. So, just the opposite from what he describes is currently happening. The southern Amazon transition forest is experiencing more drought, longer dry seasons, and more fire. Wet season river flooding and sedimentation has also increased in this region — another indicator of forest decline. While increasing CO2 concentrations can increase productivity of many plants, drought and fire are the big determinants of tree growth in the southern Amazon.”
“Worstall’s rant about widespread Amazon forest dieback reinforces my view that this is a distraction — let’s look at the evidence at hand where forest meets savanna — it is moving more towards savanna, not towards more forest.”
Dan Nepstad, Director at the Amazon Environmental Research Institute (IPAM), agreed.
In his column, Worstall belittled the risks of deforestation to tropical forests, writing “Good news for those of us who like our unsustainable tropical hardwood furniture: it looks like there’s going to be a lot more of it to go around soon enough.”
Worstall also exaggerates proposed solutions for reducing greenhouse gas emissions: “Of course what we’re told we have to do about it, closing down industrial civilization, is simply crazed lunacy. Better to lose all the forests than have to return to rural peasantry for all.”
“After studying the Amazon rainforest for 28 years, it is clear that one third or more of this mighty ecosystem is vulnerable to severe degradation through the interacting influences of devastating droughts, fire, forest conversion to crops and pastures, and logging. What is most worrisome is that this process of degradation is self-reinforcing — fire begets fire; drought begets drought. The severe weather episodes associated with climate change may already be pushing the forest-climate-fire system towards a tipping point of cascading forest degradation. These effects swamp the slightly faster growth rates that we are seeing in some Amazon trees that may be the result of higher CO2 levels.”
William F. Laurance, an ecologist at James Cook University in Australia, told mongabay.com that these other factors make it far too soon to begin assuming tropical forests are set to expand.
“Mr Worstall’s comments are a bit ridiculous, really,” said Laurance. “Yes, it’s true that, where disturbances are limited, rising CO2 levels might help give trees a competitive edge with grasses. And it’s also true that some tropical forests are slowly getting more massive, quite possibly because of CO2 fertilization.”
“But to suggest this means our worries for rainforests are over is patently silly. There are a whole constellation of factors—such as bulldozers, fires, chainsaws, and rapidly expanding road networks—that are knocking down rainforests every day. Forest destruction is happening a whole lot faster than forest expansion.”
Photo: Rhett A. Butler
“We live in an era of rapidly shrinking rainforests, and all signs suggest that is only going to continue, especially in a world with up to 10 billion people in it.”
Worstall’s editorials come two years after Jonathan Leake, Science & Environment Editor of the Sunday Times, triggered the Amazongate scandal when he claimed that studies forecasting a potential die-off of the Amazon rainforest were bogus. Scientists quickly refuted the story and a subsequent investigation revealed the die-off scenario was indeed backed by scientific research.
The debacle led to Sunday Times retracting the piece and issuing an apology, acknowledging journalistic misconduct in the handling of the story.
Adapted from Scientists slam Telegraph blogger’s claims that climate change will be good for the Amazon by Rhett A. Butler, mongabay.com.
Mongabay.com provides news, information, and analysis on environmental issues, with a special focus on tropical rainforests. The web site features more than 70,000 photos and has a section about forests for children available in nearly 40 languages.
Editor: Lara C.
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