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Organic Vapours from Boreal Forests can Cool the Climate
A new paper has been published:
Spracklen, D.V., Bonn, B., Carslaw, K.S. (2008), Boreal Forests, Aerosols and the Impacts on Clouds and Climate, Philosophical Transactions of the Royal Society A, 366, doi:10.1098/rsta.2008.0201.
The Abstract states:
Previous studies have concluded that boreal forests warm the climate because the cooling from storage of carbon in vegetation and soils is cancelled out by the warming due to the absorption of the Sun’s heat by the dark forest canopy. However, these studies ignored the impacts of forests on atmospheric aerosol. We use a global atmospheric model to show that, through emission of organic vapours and the resulting condensational growth of newly formed particles, boreal forests double regional cloud condensation nuclei concentrations (from approx. 100 to approx. 200 cm-3). Using a simple radiative model, we estimate that the resulting change in cloud albedo causes a radiative forcing of between -1.8 and -6.7 Wm-2 of forest. This forcing may be sufficiently large to result in boreal forests having an overall cooling impact on climate. We propose that the combination of climate forcings related to boreal forests may result in an important global homeostasis. In cold climatic conditions, the snow–vegetation albedo effect dominates and boreal forests warm the climate, whereas in warmer climates they may emit sufficiently large amounts of organic vapour modifying cloud albedo and acting to cool climate.
Keywords: boreal forests; climate feedbacks; aerosols; cloud condensation nuclei; climate mitigation; new particle formation
The paper concludes:
This work has important policy implications. Previous studies have suggested that climate mitigation through forest expansion in the boreal zone would warm climate. Our study questions this conclusion. Climate model studies that comprehensively evaluate all of the influences of forests on climate are now required. Our study focused on the impacts of forest terpenes on aerosol, but other biogenic aerosol and trace gas sources may also be important.
We propose that a combination of climate forcings may result in boreal forests acting to help stabilize regional and global temperatures. During cold climatic periods, a dominant snow–vegetation albedo forcing results in boreal forests warming climate. In warm climatic periods, this forcing becomes less important and the forest–aerosol–cloud albedo forcing may dominate, resulting in boreal forests cooling climate. This impact of boreal forest on aerosol and clouds represents an important climate feedback process that must be included in climate models in order to make realistic predictions.
November 25th, 2008 at 6:58 am
[...] 10) Previous studies have concluded that boreal forests warm the climate because the cooling from storage of carbon in vegetation and soils is cancelled out by the warming due to the absorption of the Sun’s heat by the dark forest canopy. However, these studies ignored the impacts of forests on atmospheric aerosol. We use a global atmospheric model to show that, through emission of organic vapours and the resulting condensational growth of newly formed particles, boreal forests double regional cloud condensation nuclei concentrations (from approx. 100 to approx. 200 cm-3). Using a simple radiative model, we estimate that the resulting change in cloud albedo causes a radiative forcing of between -1.8 and -6.7 Wm-2 of forest. This forcing may be sufficiently large to result in boreal forests having an overall cooling impact on climate. We propose that the combination of climate forcings related to boreal forests may result in an important global homeostasis. In cold climatic conditions, the snow–vegetation albedo effect dominates and boreal forests warm the climate, whereas in warmer climates they may emit sufficiently large amounts of organic vapour modifying cloud albedo and acting to cool climate. This work has important policy implications. Previous studies have suggested that climate mitigation through forest expansion in the boreal zone would warm climate. Our study questions this conclusion. Climate model studies that comprehensively evaluate all of the influences of forests on climate are now required. Our study focused on the impacts of forest terpenes on aerosol, but other biogenic aerosol and trace gas sources may also be important. We propose that a combination of climate forcings may result in boreal forests acting to help stabilize regional and global temperatures. During cold climatic periods, a dominant snow–vegetation albedo forcing results in boreal forests warming climate. In warm climatic periods, this forcing becomes less important and the forest–aerosol–cloud albedo forcing may dominate, resulting in boreal forests cooling climate. This impact of boreal forest on aerosol and clouds represents an important climate feedback process that must be included in climate models in order to make realistic predictions. http://climateresearchnews.com/2008/11/organic-vapours-from-boreal-forests-can-cool-the-climate [...]