29 September 2010

Geoengineering Today

Geoengineering . . . You're Looking At It

[crossposted from Doc's Green Blog]

"Geoengineering" refers to large-scale efforts to manipulate the climate. There are several current and recent activities that have been undertaken for other purposes, but which have the effect of changing climate, for good or ill.

We will set aside the deliberate release of 25 billion tonnes of greenhouse gases from combustion of fossil fuels each year, a geoengineering "experiment" that seems already to be creating many interesting effects. Although this is one of the largest geoengineering projects ever undertaken, it has been discussed in some detail elsewhere.

The three current geoengineering programs this post will consider are:
  • China's "Great Green Wall"
  • Large-scale expansion of irrigation
  • Large-scale deforestation

Afforestation Changes The Climate

Since 1978 China has been engaged in a vast project that has been called the "Great Green Wall". In 1981 the National People’s Congress passed a resolution to require every citizen above age 11 to plant at least three Poplar, Eucalyptus, Larch or other saplings every year. [Source] Afforestation has already covered 500,000 square kilometres with new artificial forest, and China hopes to have such forests on 400 million hectares--more than 42% of its land area--by 2050.

Chinese Vice Premier Hui Liangyu recently called for even greater efforts to increase China's forest cover.

The immediate goal of this program is to slow the encroachment of desert from the north and west into areas formerly grassland. Whether artificial forests can do this remains to be seen. And there are some concerns about other effects, such as increased water use. [More at Wikipedia.] A similar effort was the shelterbelt program in the U.S. Great Plains in the 1930s, but that was not on a Chinese scale.

Since forests affect the water cycle, albedo, and cloud cover of an area they can be expected to modify the local climate, and perhaps the climate downwind.

Irrigation Changes The Climate

Large programs of crop irrigation in Asia and North America result in large quantities of water evaporating from fields and water channels, and by transpiration through plants.

Because of the latent heat of water, more evaporation means more cooling in some places, and more rain means more warming in other places. (What is latent heat? See this post at Science In Action.)  A recent article in the Journal of Geophysical Research (pdf here, New York Times Green blog post about it here) says irrigation may be causing cooling in some regions, locally masking the effects of global warming.

The model runs reported in this paper suggest that parts of northern India may have experienced several degrees of cooling due to all the heat absorbed by irrigation water applied to crops in the later part of the 20th century. Weather patterns may even have been affected enough to reduce the amount of rain in the Bay of Bengal branch of the Southwest Monsoon. (Other researchers got somewhat different or even contradictory results with different models.)

This is a bit scary because if groundwater depletion leads to reduction in irrigation in the future, the resulting reduction of cooling effect could have both local an regional climate effects, including sharply higher temperatures and changes in rainfall amounts and distribution.

Deforestation Changes The Climate

Large-scale deforestation for conversion of forest to pasture or cropland is an old story.  Such deforestation took place over much of Europe and temperate North America in earlier centuries. A similar massive land-use change was the breaking up of the American prairie grasslands for farming in the 19th century.

When forests are burned (the usual method) to clear them for agriculture the carbon trapped in the trees is dumped into the atmosphere. Soot and other particulates are also released in great quantities. Both CO2 and black carbon have significant local and global effects on climate.

The Nature Conservancy says "deforestation and land use change contributes approximately 20 to 25 percent of the carbon emissions that cause climate change." This Wikipedia article on per-capita greenhouse gas emissions by country, which uses data from the World Resources Institute for 2000, suggests land-use changes account for about 17% of greenhouse gas emissions.

So land-use changes, mostly deforestation, annually release about the same amount of greenhouse gases as the USA or China does from all burning of fossil fuels.

The Future of Geoengineering

Several enormous geoengineering projects have been discussed as ways to undo some of the damage the earlier geoengineering projects mentioned above are causing. This previous post looks at some of the limitations and potential impacts of such schemes. Whether such consequences are "unintended", "unavoidable", or "somebody else's problem" will be part of the discussion of these projects in years to come.

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