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Methane (CH4)
introduction

 
   
 
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page last modified:
23 January 2004
   
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NOTE:
the data product Methane has been removed
from the TEMIS project.

 


 

Methane

Methane, CH4, is a greenhouse gas and the primary gas in Kyoto protocol. Large increases in methane concentration are observed since pre-industrial (a 150% increase, from 750 to 1750 ppb).

Methane is going to be a new product: it will be derived from SCIAMACHY near-infrared channels. What will be delivered are total methane columns with an anticipated accuracy of about 1%. As the example below shows, the variability due to the uncertainties in the emissions is a 1-2%, and so detection of emissions is perhaps possible.

Problematic is that there are large uncertainties in the estimates of methane sources (e.g. fossil fuels, cattle, rice agriculture, landfills, wetlands) and that methane is a well-mixed gas in the troposphere. Another aspect is that the methane column value varies with the surface pressure (i.e. with the local surface height), which has to be corrected for to be able to compare column values.
 

Model example

The following graph shows the result of an explicit modelling of methane emissions for June 1997 in Dobson Units (DU). Note that the step between the contours 20 DU or about 1-2%. The regions of high methane emissions in Eastern Europe and Asia are clearly visible.

 

modelled methane column, June 1997

 
The chemistry-transport model that produced the above image was run for 10 days, with the approriate meteorological information. And the same was done with a 50% increase in the emissions (a reasonable estimate of the variability of the emissions). The following graphs shows the difference after 10 days between the methane columns of these two model runs. Note that the scale runs up to 20 DU or 1% of the total methane column as showns in the picture above. In other words, the variability in the methane column due to uncertainties in the methane emissions is around 1%. (The moderately high values above Central Afrika and South America are due to biomass burning events.)

 

methane column difference after 10 days

 
Some 10-20% of the methane column is in the stratosphere and its variability is a few percent, as the following graph shows.

 

stratospheric methane column