Following the discussion about old-growth forests and their ability to capture carbon dioxide (CO2), I shall now discuss afforestation as a potential solution for mitigating climate change. Afforestation is the establishment of a forest where previously there was no forest.
Therefore desalination of sea water was found to be the most appropriate source of water for irrigation. The cost of which had dropped in 2008 to $0.53 per cubic meter of fresh water. Several other costs need to be considered when using desalination and irrigation systems such as distribution costs, cost of electricity, maintenance costs, construction costs, and the risk of leakage of sequestered CO2.
Ornstein et al (2009) find that afforestation of subtropical deserts sequesters 8 Gt C per year. However, they estimated that 8.8 Gt C per year is required to mitigate climate change and so this method cannot be the only method used. They argue that the costs involved with afforestation of subtropical deserts need to be weighed against potential costs of recovering from the impacts of global warming such as drought and flooding.
The article briefly mentions possible environmental issues with the afforestation of subtropical deserts but explains in details the economic costs. I think that there should be much more emphasis on these environmental issues. For example, a forest in the Sahara will dramatically reduce the dust content which is thought to suppress hurricanes that originate in the Atlantic. Therefore the hurricanes which hit the Gulf of Mexico could be stronger.
There is also the issue of the highly saline waste water from the desalination plants. The water would need to be diluted before being put back into the ocean so that the thermohaline circulation is not disrupted and hyper-saline anoxic areas are not created.
Fire is also another issue because the ground litter will be dry. Therefore investment in firebreaks would be necessary.
It is clear that more research is needed before this can ever be put into practice. Ornstein et al (2009) seem to be enthusiastic about this method of mitigation however even they recognise that more understanding about induced rainfall and climatic teleconnections are needed.
According to Ornstein et al (2009), afforestation on such a large scale will still not remove enough CO2 to halt global warming therefore maybe smaller scale projects could work in combination with other methods.
This video explains the afforestation project which is happening in China.
Ornstein, L, I. Aleinov, D. Rind (2009) 'Irrigated afforestation of the Sahara and Australian Outback to end global warming', Climatic Change, 97, pp. 409-437
DOI 10.1007/s10584-009-9626-y
an interesting post hollie. i'd not heard about reforesting desert regions to help mitigate climate change. certainly in the early holocene regions such as the sahara were wetter and greener.
ReplyDeletehave any modelling studies been done to see what impact afforestation might have on climate change?
The study mentioned above used modelling to find what impact the afforestation would have on the climate. Ornstein et al (2009) used the GISS GCM ModelE with two ocean models. There was a Fixed Ocean (FO) model and Russell’s Dynamic Coupled Ocean model (DCO). Some of the results are shown below. In the figure a and b show annual precipitation over an irrigated Sahara. (I can't seem to get the figure on to this but it is figure 3 in the paper cited in the post.) The FO model shows precipitation of between 700 and 1200 mm/year and for DCO 1000 mm/year. They also found that the effects on precipitation were local. However, the rainfall was seasonal because it began in April and ended in November and so heavy irrigation would be needed for the rest of the year.
ReplyDeleteOverall, models have shown that only tropical afforestation has the potential to mitigate climate change because new forests in the tropics lead to increased evapotranspiration and therefore increased cloudiness (Bale, 2009). Increased cloudiness causes less surface solar radiation which has a cooling effect. This is in addition to the cooling from CO2 sequestration. Models also show that afforestation in the high latitudes can accelerate global warming because boreal forests would decrease the surface albedo which is normally quite high because of the snow (Bale, 2009). Therefore more surface radiation will be absorbed.
Bale, G (2009) ‘Problems with geoengineering schemes to combat climate change’ Current Science, 96, 1, pp. 41-48