Tuesday, June 21, 2011

Afforestation no substitute for reducing CO2 emissions



A new scientific study published in Nature Geoscience says that major afforestation will have little impact on slowing global warming and that "afforestation is not a substitute for reduced greenhouse-gas emissions".


The study was authored by Vivek K. Arora & Alvaro Montenegro and published in Nature Geoscience on 19 June 2011. The authors argue that forests are less reflective than croplands, and the absorption of incoming solar radiation is greater over afforested areas resulting in net climate warming particularly at high latitudes.

International climate negotiations focus on afforestation as a key climate change mitigation strategy for storing carbon, providing 'offsets' for continued greenhouse emissions. But climate negitiators fail to take into account the albedo affect of forests. In mid and high latitudes the forests absorb more sunlight increasing temperatures, while in the tropics the high rate of evaporation has a slight cooling effect on temperatures.

The study found that warming reductions per unit afforested area are around three times higher in the tropics than in the boreal and northern temperate regions. The study suggests that stopping deforestation and continued afforestation in the tropics are effective forest-management strategies from a climate perspective.

Using a comprehensive Earth system model to assess the climate-change mitigation potential of forests under different scenarios the study says that if 100% of cropland was turned to forests it would provide reduced warming of around 0.45°C, and for 50% forests about 0.25°C.

"Temperature benefits associated with more realistic global afforestation efforts, where less than 50% of cropland is converted, are expected to be even smaller, indicating that afforestation is not a substitute for reduced greenhouse-gas emissions." says the report abstract.

Here in Australia we have Opposition Leader Tony Abbott whose climate mitigation "direct action" plan involves planting 20 million trees by 2020. But planting trees is no substitute for actually reducing greenhouse gas emissions. Australia is also overly reliant on REDD climate offsets. Where original tropical forests can be preserved these offsets provide a valuable benefit, but often the offset mechanism has been used for deforrestation and then plantation farming which contributes carbon emissions.

Related:
* Jan 28, 2011 - Forests are not commodities - REDD under fire for narrow focus on carbon storage
* New Scientist, June 19 2011 - Planting forests won't stop global warming

Source:
Nature Geoscience (2011) doi:10.1038/ngeo1182 abstract - Small temperature benefits provided by realistic afforestation efforts by Vivek K. Arora & Alvaro Montenegro