Friday, September 28, 2012

Methane levels increasing - why?

This is interesting.

Atmospheric methane levels, having been flat for five years, have begun to go up again. 

Sussmann, Forster, Rettinger & Bousquet 2012
Above we see growth in levels of atmospheric methane brisk 1986-98, then levelling off, and since 2006, picking up again. Zugspitze and Garmish refer to measurements at 2 different locations, Z being high up (2964 m above sea level, and G being 743 m asl). There is more methane lower down.

In their paper Sussmann et al  comment on their findings:

This is either the longest and largest positive trend anomaly
since the beginning of systematic observations more than 25
years ago or the onset of a new period of strongly increasing
CH4 levels in the atmosphere.

I don't see much of an either/or there, more of a both/and.

They speculate on the cause of the increase. About 3/4 of the methane is attributed to tropical wetlands, which saw  20 year-record rainfall levels in 2007 and 2008, so more methane (CH4) emissions from natural wetlands is one possibility.

One quarter is attributed to methane of polar origin. But why is it going up, when the temperature has not been going up of late?

Or has it? In the North, where the bogs and tundra are located?

Take a look at this:

Source: Climate4You
I like using Climate4you because it is a skeptic's website, which means that I cannot be accused of pro-warming science sources. 

We see that Arctic temperatures have been rising steadily, apart from a fall from 2007-2009. When the methane levels were increasing. It is unlikely therefore that the increases can be attributed to melting tundra &c.

Sussmann says:
Finally, no evidence of strongly increased emissions from
stores of carbon in melting permafrost and from marine hydrates as a reaction to climate change can be found today from atmospheric observations. However, both will remain
potential sources of severely increasing methane emissions
in the future, which should be monitored closely by remote
sensing at the surface or from space.

He is saying that we have not even begun to see the release of methane from the soil or the sea. But they are there, waiting.

Methane is a greenhouse gas about 30 times as potent as CO2, but present in smaller concentrations, so that it represents only about 4-9% of the total of warming gases.
The main greenhouse gases are, in terms of their effect :

  • water vapor, 36–70%
  • carbon dioxide, 9–26%
  • methane, 4–9%
  • ozone, 3–7%
    (source: Wikipedia
Wikipedia explains the wide variation thus: It is not possible to state that a certain gas causes an exact percentage of the greenhouse effect. This is because some of the gases absorb and emit radiation at the same frequencies as others, so that the total greenhouse effect is not simply the sum of the influence of each gas. The higher ends of the ranges quoted are for each gas alone; the lower ends account for overlaps with the other gases.[11][12] In addition, some gases such as methane are known to have large indirect effects that are still being quantified.[17] 

Methane has doubled since industrialisation, and the present rate of increase 1996- 2012 means, I calculate, a 6.6% increase over 16 years. (That is, a 6.6% increase on its 3-7%, not an increase from 9.6 to 13.6%).

Methane has complex indirect effects which will amplify its direct warming effect.

Mercifully, this is still not a lot. Even so, it is a positive feedback, and all positive feed-backs need to be avoided if at all possible.

With all those billions of tonnes of methane locked up in the frozen poles, we need to take our foot off the gas and start thinking about hoisting the sails. As it were.

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