Scientists query future power of "carbon sinks"
Date: 24-May-01
Country: UK
Author: Patricia Reaney
Researchers at the University of Michigan and Duke University in North Carolina have completed a seven-year study which raises doubts about the ability of forests, so-called carbon sinks, to soak up the excess CO2 being pumped into the atmosphere from exhaust pipes and smoke stacks.
Using forests to fight global warming, a plan backed by the United States, was one of the disputed points at the heart of the failed U.N. climate conference in The Hague last year.
The new research by the American scientists shows a shortage of water and nutrients in the soil could limit how trees respond to increases in CO2.
"In terms of rising atmospheric CO2, I believe we need to consider the fertility of the site when we are thinking about how much carbon sequestration (absorption) we have now and how much we can project in the future," David Ellsworth said in a telephone interview yesterday.
The finding does not change the situation very much for current carbon sinks, he said, but it could have serious implications on future predictions.
"If we are trying to value future carbon sinks, this could be incredibly important in the sense that future carbon sinks may not be as large as we have anticipated based on shorter-term studies and modelling activities," Ellsworth added.
The assistant professor of plant physiological ecology and colleagues examined the effects of elevated CO2 on forests with limited nutrients over many years. They also exposed trees to increased CO2 to simulate conditions predicted in 50 years time.
ROLE OF SOIL ALSO QUESTIONED
Their results are reported in the current issue of science journal Nature along with a study by other Duke scientists which questions the role of soils as long-term carbon sinks.
Until now the impact of soil nutrients has not been considered as a factor in a tree's ability to absorb CO2, but Ellsworth and his colleagues said it should be.
"The debate over how much CO2 trees will absorb should consider the limitations of soil fertility or other key resources in low supply," he said.
"It makes the playing ground a lot more complicated to evaluate," Ellsworth added.
The dispute between the European Union and the United States at the climate talks was mainly over carbon sinks. The U.S. plan called for developed nations to be allowed to count CO2 soaked up by forests against targets for cutting greenhouse gas emissions.
Opponents of the scheme argued that it could lead to a rise in global emissions.
"I don't think we can assume existing forests, with their fertility limitations, will completely offset rising CO2 without soil amendments," said Ellsworth.
"We will more likely find solutions in measures such as burning less fossil fuel and planting more trees in high-nutrient soils," he added.
But the scientists cautioned that adding nutrients to the soil may involve other negative effects on the environment.
