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Atmospheric CO2 increased to 379ppm in 2005 (Figure 3). Ice core
records reveal that we have left the domain that defined the Earth
system for the 420,000 years before the Industrial Revolution (4) in a
speed never occurred before (Figure 3).
CO2 is the most important
anthropogenic GHG and its annual emissions grew by about 80% between
1970 and 2004. The current level exceeds by far the natural range over
the last 650,000 years. The in-creases in GHG concentrations are mainly
caused by fossil fuel burning and land-use change provides another
significant contribution (Figure 5)
Greenhouse Gas (GHG) Emissions from Agriculture
Measurable anomalous emissions of GHG began already 8000 years ago.
These early anthropogenic CO2 emissions were caused by forest clearing
in Eurasia for agricultural purposes, and methane (CH4) emission rose
from widespread rice irrigation about 5000 years ago (6). After 1750
the increase in atmospheric CO2 was mainly caused by fossil fuel
combustion but emissions from land use change contributed about 30%,
from which more than half is estimated from depletion of carbon in the
soil. This depletion is exacerbated by further soil degradation and
desertification (7). The total soil carbon (organic and inorganic) is
3.3 times the size of the atmospheric carbon pool (1). As most
agricultural soils have lost 50 to 70% of their original carbon (7)
they represent a considerable carbon sink if efforts are made to
restore soil organic carbon, but also a huge source of GHG if soil
management and deforestation rates are not changed. There is high
agreement and much evidence that with current climate change mitigation
policies and related sustainable development practices, global GHG
emissions will continue to grow over the next few decades (25-90%
between 2000 and 2030) (8).
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| Figure 3 increases in the most important greenhouse gases (www.ipcc.ch) |
Figure 4 use of fossil energy (nat-ural gas) for nitrogen (fertilizer) synthesis |
Read about The Importance of Soil Organic Carbon
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