Afforestation of the Sahara and Australian Outback

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. 


The study by Ornstein et al (2009) investigated the possibility of using the Sahara and the Australian Outback as areas for afforestation. The Sahara and Australian Outback are extremely dry and arid areas; therefore the forests would have to be irrigated. The possible water supplies considered were the groundwater because the Sahara has the largest store of groundwater. However, the groundwater would only be able to support the irrigated forest for a few years.  They noted that the irrigation may only be required for the early establishment and afterwards biogeophysically-induced precipitation would be capable of supporting the forest. The study found that the amount of biogeophysically-induced precipitation would not be enough to support the forest especially if rainfall was seasonal.

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 CO_2.

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

http://www.springerlink.com/content/55436u2122u77525/

Geothermal Energy in Newcastle

Engineers have started drilling a 2000m hole in Newcastle today in order to use geothermal energy. The project will hopefully result in 80⁰C water being used to heat the buildings in the surrounding area. The first hot water is due to be pumped out by June.

See full article and video here:

http://www.bbc.co.uk/news/uk-12549886

This is a positive step towards lower emissions of carbon dioxide for the UK. The project is estimated to cost £900,000 so hopefully it will succeed. The long term cost of geothermal energy is minimal and is continuously available because it doesn’t rely on any environmental factors such as, wind or sun. If the project is a success then hopefully the government will allocate funding to implement geothermal energy nationwide. 

Old-growth forests

There has been a long-standing view that old-growth forests are carbon neutral because it was thought that photosynthesis (carbon dioxide uptake) was equivalent to respiration (carbon dioxide release) (Luyssaert, 2008). However, this understanding is based on ten years of data collection from one site (Luyssaert, 2008). Unfortunately this has led to old-growth forests not being protected by international treaties.

Luyssaert et al (2008) investigated the view that old-growth forests are carbon neutral by compiling data from 519 sites. They found that in forests aged between 15 and 800 years the net carbon balance is usually positive. Therefore old-growth forests can continue to remove carbon dioxide from the atmosphere and store the sequestered carbon dioxide in woody tissue and soil.

Contrastingly, Luyssaert et al (2008) found that young forests can be sources of carbon dioxide because the disturbance resulting from creating a new forest causes a greater decomposition rate than the net primary production of the regrowth.

Another important issue which arises from the article is that it is more unlikely for an old-growth forest to become a carbon source than an even-aged plantation. If an old-growth forest was to undergo some disturbance then there is usually another canopy of trees which can continue the productivity of the ecosystem. Also tree mortality and regeneration is quick whereas decomposition can be on a decadal scale. Therefore contribution of carbon dioxide to the atmosphere through decomposition is a slow process and so old-growth forests do not necessarily become carbon sources. Even-aged plantations do not have the same insurance of a secondary canopy and therefore if tree mortality occurs they can become carbon sources (Luyssaert et al, 2008).

Old-growth forests have accumulated carbon for centuries. There is the possibility that this carbon could be released back into the atmosphere if the forests are disturbed. The exclusion of old-growth forests from the Kyoto Protocol was based on the carbon neutral hypothesis. However, there is an increasing international understanding about the importance of forests and the impact deforestation has on the climate. Luyssaert et al (2008) stress the need for old-growth forests to be protected by the international community.

Apart from increasing understanding about the ability of old-growth forests to capture and store carbon dioxide, Luyssaert et al (2008) have highlighted potential issues with schemes of reforestation. Plantations with trees of similar ages can be potentially dangerous for the environment because if fungal attacks occur, the trees die and there is no secondary canopy to continue uptake of carbon dioxide. Therefore carbon dioxide release would exceed carbon dioxide uptake and the plantation would become a carbon dioxide source.

This study completely changes the understanding of old-growth forests and therefore further research should be applied to this area. Research should focus in particular on the impacts of planting even-aged plantations to mitigate climate change. There needs to be an increased emphasis on protecting these valuable ecosystems on an international scale. 

Luyssaert, S., E. Detlef Schulze, A. Börner, A. Knohl, D. Hessenmöller, B. E. Law, P. Ciais, and J. Grace (2008) 'Old-growth forests as global carbon sinks' Nature, 455, pp.213-215

doi:10.1038/nature07276

Old-growth forests as global carbon sinks 

Aim of Cleaning Climate

The aim of Cleaning Climate is to identify whether geoengineering should be the focus for mitigating climate change. In order to achieve this aim the natural processes which have in the past taken carbon  dioxide (CO₂ ) out of the atmosphere will be discussed. These processes are split into oceanic and terrestrial processes. Human methods for CO₂ reduction will also be discussed for example, ocean fertilisation, and afforestation. The discussions will involve looking at different research articles to identify the advantages and disadvantages of the different methods.