Amazon under threat from cleaner air

May 07, 2008
Sky, Clouds

The Amazon rainforest, so crucial to the Earth’s climate system, is coming under threat from cleaner air say prominent UK and Brazilian climate scientists in the leading scientific journal Nature.

The new study identifies a link between reducing sulphur dioxide emissions from burning coal and increasing sea surface temperatures in the tropical north Atlantic, resulting in a heightened risk of drought in the Amazon rainforest.

The Amazon rainforest contains about one tenth of the total carbon stored in land ecosystems and recycles a large fraction of the rainfall that falls upon it. So any major change to its vegetation, brought about by events like deforestation or drought, has an impact on the global climate system.

A team from the University of Exeter, Centre for Ecology and Hydrology, Met Office Hadley Centre and Brazilian National Institute for Space Studies used the Met Office Hadley Centre climate-carbon model to simulate the impacts of twenty-first century climate change on the Amazon rainforest. They compared the model to data from the 2005 drought, which caused widespread devastation across the Amazon basin. The researchers estimate that by 2025 a drought on this scale could happen every other year and by 2060 a drought could occur in nine out of every ten years.

Co-author Dr Matthew Collins of the Met Office Hadley Centre puts this into context: “The rainforest is under many pressures. Direct deforestation is the most obvious immediate threat, but climate change is also a big issue for Amazonia. We have to deal with both if we want to safeguard the forest.”

Co-Author Dr Carlos Nobre of the Brazilian Institute for Space Research adds: “Global warming, deforestation and increased forest fires are all acting in synergy to reduce the resilience of the Amazonian forests”.

Sulphate aerosol particles arising from the burning of coal in power stations in the 1970s and 1980s have partially reduced global warming by reflecting sunlight and making clouds brighter. This pollution has been predominantly in the northern hemisphere and has acted to limit warming in the tropical north Atlantic, keeping the Amazon wetter than it would otherwise be. Chris Huntingford of CEH, another of the co-authors, explains: “Reduced sulphur emissions in North America and Europe will see tropical rain-bands move northwards as the north Atlantic warms, resulting in a sharp increase in the risk of Amazonian drought”.

Lead author Professor Peter Cox of the University of Exeter sums-up the consequences of the study: “These findings are another reminder of the complex nature of environmental change. To improve air quality and safeguard public health, we must continue to reduce aerosol pollution, but our study suggests that this needs to be accompanied by urgent reductions in carbon dioxide emissions to minimize the risk of Amazon forest dieback.”

Source: University of Exeter

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CWFlink
5 / 5 (6) May 07, 2008
Over a year ago Nova has a show on the fact that particulate matter in the air contributed to clouding that impacted sunlight reaching the gound. It was pointed out that global warming was being countered by polution that led to clouds that led to sunlight being reflected. I've joked that, as a result, "smog reduction programs" are a cause of global warming. A recent article on the melting of Arctic ice suggested that the clear skys over the Arctic recently was the cause. So again, we're faced with the realization of how little we know: we bend over backwards to stop polution to obtain "cleaner skys" and find an unintended consequence is deforestation, desertification and a greater global disaster than we started with. Sad commentary on our ignorance about life on earth. National Geo's special on China deepens that sadness. Nature's solution is well known: massive die-off. In our case, it will come via wars springing from overpopulation and starvation. There is no justification for telling the 3rd world they must die so we can live. There is no way we can feed them; they must feed themselves. So much of what we CAN do may simply prolong their suffering. I'm totally bumbed-out. Got a clue?
Soylent
4 / 5 (5) May 08, 2008
Flink, it's been known since at least the 60's that sulphate particulates are an important negative forcing and that other particulates bias the temperature distribution higher up into the atmosphere(see "global dimming").

The reason we've tried to stop emitting particulates and smog at the ground level is not for "clean skies" per se; it was to reduce the horrific death toll, reduce the rate of corrosion of our structures and vehicles and reduce the ecological impact of acid rain.

Many studies have been done on releasing sulphate particulates high into the atmopshere as a countermeassure to climate change. It is known that it is very cost effective and reasonably compensates for global warming temperature wise. There are various suspected drawbacks(e.g. ozone depletion, change of some weather patterns). The effect on plants and agriculture due to decreased sunshine is believed to be slight and positive; this seems paradoxical until you note that sulphate particles in addition to reflecting some light back into space also decrease the direct lighting from the sun and increases the diffuse lighting from the sky which lits up plants more evenly.