Thursday, 12 November 2015

Amazon Deforestation and Climate Change

In last week's post we explored the relationship between humans and deforestation in the African continent. Now we are flying a few thousand miles across the Atlantic to explore the relationship between deforestation and global (and local) climate change in the Amazon.

The Amazon Rainforest is one of the most beautiful and captivating locations on our planet and hosts roughly half of the world's species and covers an area of 5.4 million km2 (62% of Brazil).

Outstanding Natural Beauty - the Amazon is at risk (source)
How does deforestation alter the landscape and effect local climate?
The removal of lowland tropical rainforests in the southern and eastern parts of the Amazon jungle for cattle ranches and soybean production means that trees are being replaced by grass.
Shukla et al. (1990) undertook numerical modelling to evaluate the effects of deforestation on local and global climate. They found that there would be an rise in surface temperature and a reduction in evapotranspiration and precipitation would cause an increase the duration of the dry season (supported by Malhi et al. 2008). This was also modeled in the 2007 IPCC report which showed a decrease in dry season rainfall but an increase in rainfall in the western Amazon during the wet season. Shukla et al's work is convincing yet dated and the recent work by Malhi et al. (2008) explores the climatic effects of deforestation one step further.

Evaporation and condensation over the Amazon  are the locomotives driving global atmospheric circulation. Furthermore, 25-50% of rainfall is recycled from forests which is important in places, such as the Amazon, where precipitation is a consequence of regional convection (Shukla et al. 1990). Removing the trees reduces rainfall, decreases cloudiness and increases insolation. It also alters the surface roughness increasing wind speed and therefore desertification and soil erosion. The changes to local scale climate are extensive.
% Change in Rainfall due to deforestation. Red shows the areas that will experience large decreases in rainfall. This are often the areas where the greatest deforestation occurs (NOAA)
How does deforestation alter global climate?
An incredibly recent study by Exbrayat and Williams (2015) showed that Amazon deforestation had a net contribution of 1.8ppm of atmospheric CO2 or 1.5% of historical growth which reflects the significance of the Amazon in the global system. It reinforces the argument that deforestation directly contributes to climate change (much in the same way as burning fossil fuels).
Malhi et al's (2008) work also touched upon the global carbon cycle and climate change talking about the release of stored carbon from trees and within the soil following deforestation. Soil carbon is released when the tree roots that hold rainforest detritus together are no longer present and the soil is eroded through aeolian and fluvial processes.

Significance and Future
As these articles and pieces of research demonstrate, the Amazon rainforest is an important component in the Earth system. It is vital for so many species including our own (Feeley and Rehm 2012). However, if nothing is done the Amazon rainforest could be completely gone within 50-100 years (Shukla et al. 1990). An increased rate of deforestation is chronicled in an interesting article by the Guardian written last year.Huge amounts of research continues to be conducted in the Amazon because it is a site of outstanding scientific interest.
Picking up the pace - rates of deforestation in the Amazon are increasing (The Guardian)


  1. Great post Max :) Any ideas of what we can do in this country to promote Amazon rainforest protection?

    1. I think ideas surrounding afforestation or reforestation are often slow so immediate solutions revolve around policy and government but often the revenue from logging is so great that governments put the environment at risk for a bit of extra cash