28th August, 2009 - Posted by admin - Comments Off
Methane has a much shorter lifetime in the atmosphere than carbon dioxide so to compare the effect of an extra tonne of methane released into the atmosphere with an extra tonne of carbon dioxide, it is usual to choose a fixed number of years over which the comparison is made. See Wikipedias entry on Global Warming Potential (GWP):
The usual number for the GWP of methane is measured over 100 years (GWP100). This sets methane at 25 times carbon dioxide. But some say that, because climate change is urgent, we need ways of reducing the heating caused by greenhouse gasses in timescales much shorter than 100 years. There is a the recent New Scientist Article “Methane controls before risky geoengineering, please”. It makes the case for taking control of methane emissions much more seriously and says
Methane is a much more powerful greenhouse gas than CO2. A tonne of methane is responsible for nearly 100 times more warming over the first five years of its lifetime in the atmosphere than a tonne of CO2 …
Wikipedia gives the Global Warming Potential of methane measured ofer 20 years as 72 times that of caron dioxide. In his model Adrian Williams calulates the carbon footprint of Beef and Lamb using GWP20 (methane compared to CO2 over 20 years) as well as the conventional GWP100. Using this finds 1 kg Beef has a carbon footprint equal to 25 kg CO2e.