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Global warming could turn forests from sink to source of carbon emissions

Rising temperatures could reverse the role forests play in mitigating climate change, turning them into net sources of greenhouse gases, reports a new assessment by the International Union of Forest Research Organizations (IUFRO).

The report, titled “Adaptation of Forests and People to Climate Change – A Global Assessment” and authored by 35 forestry scientists, examined the potential impacts of climate change across the world’s major forest types as well as the capacity of forest biomes to adapt to climate shifts. Among the conclusions: a 2.5-degree-C rise in temperatures would eliminate the net carbon sequestering function of global forests. Presently forests worldwide capture about a quarter of carbon emissions.

“We normally think of forests as putting the brakes on global warming, but in fact over the next few decades, damage induced by climate change could cause forests to release huge quantities of carbon and create a situation in which they do more to accelerate warming than to slow it down,” said Risto Seppälä, a professor at the Finnish Forest Research Institute and chair of the expert panel that produced the report.

Tropical forests — and their resident species — are particularly sensitive to small shifts in temperature.

Climate change, and associated shifts in temperature and precipitation, will have varying effects around the world. Some forests will benefit from warmer conditions, increased rainfall, and carbon dioxide fertilization effects, while others will suffer from increased incidence of drought, fire, and pest outbreaks.

The report says that these changes will affect ecosystem services and timber production, having social and economic implications.

Northern forests may benefit from climate change

“Since climate change is expected to have significant impacts on the capacity of forests to provide vital ecosystem services, it could have far-reaching consequences for the well-being of people living in affected areas,” the report states. “Whether changes in a given region are positive or negative will depend critically on the region-specific nature of climate change: under current projections, forest productivity will rise in some regions and decline in others.”

The report warns that decreased rainfall and increased incidence and severity of drought will put forest-dependent people in Africa at particular risk.

“A decline in forest ecosystem services reduces the ability of forest-dependent people to meet their basic needs for food, clean water and other necessities and can lead to deepening poverty, deteriorating public health and social conflict.”

The assessment also notes detrimental impacts in wealthy countries.

“Regions that, over the next 50 years, are likely to be particularly susceptible to the impacts of climate change on timber production are North America, Europe, Australia and New Zealand.”

Adaptation strategies

The report says that wider application sustainable forest management practices could help temper some impacts of climate change, but cautions that such efforts may only be a temporary reprieve in the face of rising carbon emissions.

“Even if adaptation measures are fully implemented, unmitigated climate change would, during the course of the current century, exceed the adaptive capacity of many forests,” said Professor Andreas Fischlin of the Swiss Federal Institute of Technology, who is one of the lead authors of the study. “The fact remains that the only way to ensure that forests do not suffer unprecedented harm is to achieve large reductions in greenhouse gas emissions.”

Risto Seppälä, Alexander Buck, & Pia Katila (Editors). ADAPTATION OF FORESTS AND PEOPLE TO CLIMATE CHANGE – A Global Assessment Report. Prepared by the Global Forest Expert Panel on Adaptation of Forests to Climate Change. International Union of Forest Research Organizations (IUFRO). World Series Volume 22. April 2009.

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