Tropical forest sustainabilty: a climate change boon

Improved management of the world's tropical forests has major implications for humanity's ability to reduce its contribution to climate change, according to a paper published in the international journal, Science.

The authors — Dr Pep Canadell from CSIRO and the Global Carbon Project, and Dr Michael Raupach from CSIRO — say the billions of tonnes of carbon dioxide (CO₂) absorbed annually by the world's forests represent an 'economic subsidy' for climate change mitigation worth hundreds of billions of dollars.

However, concerns about the permanence of forest carbon stocks, challenges in quantifying changes in the size of those stocks and concerns about the environmental and socio-economic impacts of reforestation programs have limited the adoption of policies designed to foster forestry activities.

"With political will and the involvement of tropical regions, forests can contribute to both climate change protection through carbon sequestration and also enhanced economic, environmental and socio-cultural benefits," Canadell said.

"Forestry activities have the economic potential to offset 2–4% of projected CO₂ emissions by 2030, with tropical regions accounting for nearly two thirds of the total offset. A key opportunity is the reduction of carbon emissions from deforestation and degradation in tropical regions."

An estimated 13 million hectares of the world's forested areas — almost exclusively in the tropical regions — are deforested annually.

Raupach says, however, reducing rates of deforestation by 50% by 2050, and stopping further deforestation when countries reach 50% of their current forested area, would avoid emissions equivalent to six years of current fossil fuel emissions by the end of this century.

"This estimate shows that even with significant continuing deforestation, the mitigation potential is large, although major changes in governance and price incentives are required to realise this potential," Raupach said.

The authors also note, however, that efforts to mitigate climate change by increasing both the overall area and volume of biota in those forests does carry the risk that events such as bushfires and insect outbreaks can release massive amounts of sequestered carbon back into the atmosphere.

"Since 2000, for example, increases in the areas of Canada's forests affected by bushfires and insect outbreaks have transformed them from a 'CO₂ sink' to a 'CO₂ source' — a situation which is expected to continue for the next 20–30 years," Canadell said.

"Forests also affect biophysical properties of the land surface, such as sunlight reflectivity and evaporation, and climate models suggest large reforestation programs in the boreal (colder) regions of the word could have limited benefits due to the replacement of large areas of reflective snow with dark forest canopies.

"Conversely, the climate benefits of reforestation in the tropics are enhanced by positive biophysical changes such as cloud formation which further reflect sunlight."