Environment, Headlines

ENVIRONMENT BULLETIN-CLIMATE: El Nino Effect on Amazon Rainforests

Danielle Knight

WASHINGTON, Dec 20 1998 (IPS) - The El Nino weather phenomenon may be causing rainforests in the Amazon Basin to emit the heat-trapping gas carbon dioxide, rather than absorbing it, say scientists.

Normally the world’s largest tropical rainforests act as a natural sponge or ‘sink’ – soaking up carbon dioxide which most scientists believe is one of the “greenhouse” gases that causes global warming.

But during the years of El Nino – the warm tropical current that appears in the Pacific – the drier and warmer weather in the Amazon caused the tropical rainforest to emit, rather than absorb, large amounts of carbon, according to a new study published Wednesday in the scientific journal Nature.

“When soil becomes dry during the El Nino phenomenon plants seem to respire less and absorb less carbon,” says Hanqin Tian, a researcher at the Marine Biological Laboratory, in Woods Hole, Massachusetts. “Soil also stores less carbon when it is dry.”

Such new observations on the flow of carbon are being closely watched by scientists worldwide as governments debate how they can get credit for preserving forests as natural ‘sinkholes’ for greenhouse gases – part of an international strategy to reduce the threat of global warming.

Most scientists believe that these gases, mainly resulting from the burning of oil, coal and gas, are responsible for heating the earth’s surface.

If current trends continue, average global temperatures could rise between one and 3.5 degrees centigrade by the year 2050. The increase in temperatures could have major climatological and environmental effects, ranging from an increasing intensity of storms to flooding and desertification, scientists say.

In Kyoto, Japan last December, industrialised nations agreed to reduce the emissions of six greenhouse gases – including carbon – by an average of six percent from 1990 levels, and to complete the reductions between 2008 and 2012.

The Kyoto Protocol, as the basic framework of the treaty is known, provides industrial countries the option to offset their greenhouse emissions by counting the carbon absorbed by their forests and other ecosystems that absorb carbon dioxide, termed ‘carbon sinks.’

Yet, at these negotiations many scientists argued that they did not understand the carbon cycle in its entirety well enough to predict how much carbon forests absorb or if the carbon absorbed by forests would remain there, notes Ashley Mattoon, a researcher at the Washington-based Worldwatch Institute

“In their view, carbon sinks shouldn’t have been entered into the treaty until more solid data on them had been collected.”

According to the latest report in Nature magazine, researchers found that, overall, the Amazon was a carbon sink from 1980 to 1994. But, year to year the amount of carbon the lush tropical vegetation mops up varied greatly, depending largely on how dry and hot the region becomes during the pedriodic appearance of El Nino.

Using data on vegetation, soil, temperature, and precipitation, the study reveals that the three strongest El Nino events (in 1982- 83, 1986- 87, and 1991- 92) corresponded with when the region acted as a weak sink or as an actual source of carbon.

In 1987 and 1992 – when El Nino made the region much drier and warmer – the region actually added 0.2 petagrams of carbon to the atmosphere. One petagram of carbon equals one billion metric tons of carbon.

In the non-El Nino years of 1981 and 1993, however, the region stored away 0.7 petagrams of carbon. In comparison, researchers said the deforestation in the Amazon in the early 1990s added 0.3 petagrams of carbon per year to the atmosphere.

Soil moisture, which is affected by both precipitation and temperature, and which affects both plant and soil processes, seemed to be an important factor concerning carbon storage, according to the study.

“Increased temperature from El Nino is not as important as the impact of dryness,” says Hanqin Tian, who designed the scientific model for which the study was based. “The real problem is the lack of moisture.”

Drier soil is believed to decrease the rate at which plants respire and take in carbon. Lack of moisture in the soil also increased the rate at which the soil emits carbon, he says.

The increasing amount of carbon concentration in the atmosphere also was believed to impact whether carbon was absorbed or emitted, he added. Such concentrations affect the ability of plants to photosynthesize but “the impact of carbon dioxide concentration needs to be studied more,” says Tian.

Despite the year-to-year fluctuations caused by weather changes, overall these areas absorb carbon from the atmosphere and therefore need to be protected.

“It is really important to protect tropical forests because when we cut them down they cannot function as a sink,” he says

 
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