All the other techniques we know about just prevent emission, nothing else,
said lead author Klaus Becker of the University of Hohenheim in Stuttgart,
Germany. Only plants are able to extract carbon dioxide from the air.
Spoken like a true biologist. The problem with plants (unlike geochemical CO2
uptake) is they usually don't store carbon long term. Solve that little problem
(CROPS, biochar, etc.) plus nutrient, water, albedo, and land use issues and
maybe you've got something? - Greg
CARBON CAPTURE:
Study proposes large 'carbon farms' to reverse rising temperatures
Elizabeth Harball, EE reporter
Published: Friday, August 23, 2013
A recent study by German researchers presents the possibility of carbon
farming as a less risky alternative to other carbon capture and storage
technologies. It suggests that a significant percentage of atmospheric CO2
could potentially be removed by planting millions of acres of a hardy little
shrub known as Jatropha curcas, or the Barbados nut, in dry, coastal areas.
But other experts raised doubts about the study's ambitious projections,
questioning whether the Barbados nut would be able to grow well in sandy desert
soils and absorb the quantity of carbon their models predict.
The researchers behind the study say Barbados nut plantations could help to
mitigate the local effects of global warming in desert areas, causing a
decrease in average temperature and an increase in precipitation. If a large
enough portion of the Earth were blanketed with carbon farms, they say, these
local effects could become global, capturing between 17 and 25 metric tons of
CO2 per hectare each year over a 20-year period.
All the other techniques we know about just prevent emission, nothing else,
said lead author Klaus Becker of the University of Hohenheim in Stuttgart,
Germany. Only plants are able to extract carbon dioxide from the air.
The studyhttp://www.earth-syst-dynam.net/4/237/2013/esd-4-237-2013.pdf,
published in the journal Earth System Dynamics, states that if 730 million
hectares of land -- an area about three-quarters the size of the United States
-- were devoted to this method of carbon farming, the current trend of rising
atmospheric CO2 levels could be halted.
Carbon farms would not compete with food production if they were concentrated
in dry coastal areas, the researchers said. In their scenario, oceanside
desalination plants, partially powered by biomass harvested from the
plantations themselves, provide a low-emissions irrigation method.
Could huge plantations change weather patterns?
The study states that the Barbados nut is uniquely suited to growing in regions
inhospitable to other crops. The plant, which produces a nonedible seed that
can be used to create biodiesel, is comfortable growing at temperatures
exceeding 100 degrees Fahrenheit. It can also withstand high levels of
contamination in the soil, making wastewater another potential source for
irrigation.
Additionally, the plant grows rapidly and develops pretty large roots below
the soil, which is important for carbon binding, said co-author Volker
Wulfmeyer, also of the University of Hohenheim. As part of their research,
Wulfmeyer and Becker traveled to a Barbados nut plantation in Luxor, Egypt, to
collect physical samples from the plants to estimate their carbon-storing
potential.
There are about 1 billion hectares of desert land in coastal areas that could
be used for Barbados nut plantations, the researchers estimate, located in
countries such as Mexico, Namibia, Saudi Arabia and Oman. If the entirety of
this land were used for carbon farming, the study found, atmospheric carbon
dioxide could be reduced by 17.5 parts per million over two decades, or 16.6
percent of the CO2 increase since the start of the Industrial Revolution.
But less ambitious projects may also have an impact. Using models, the
researchers projected that 100-square-kilometer plantations in Oman and
Mexico's Sonoran Desert could cause temperatures to fall by more than 1 degree
Celsius. The model also saw a precipitation increase of 11 millimeters per year
in Oman and 30 millimeters per year in the Sonoran.
Paradoxically, this is because plantations are darker than the surrounding
desert, explained Wulfmeyer, retaining more heat during the daytime. As a
result, a low-pressure system develops over the carbon farm, causing changes in
wind patterns that allow clouds to develop and precipitation to increase.
Mitigating global warming on a more local scale should be a big incentive for
countries to back large plantations, Wulfmeyer said: The technology is there
to do this, but it needs some enthusiasm and some idealism and some more
knowledge in the countries before it can be realized.
Barbados nut a disappointment in the past
The cost of carbon farming is comparable to the costs associated with other
carbon capture and storage technologies, the study asserts.
The researchers
