Australia: The Land Where Time Began

A biography of the Australian continent 

Arctic Methane Release – Global Impact

A release of 50 Gt of methane over 10 years was modelled by Wadhams, together with Gail Whitman and Chris Hope, both in terms of temperature and cost (Whiteman, Hope & Wadhams, 2013). Though this is a huge quantity of gas, that is seemingly impossible to let loose on the world. The total annual release of CO2 is 35 Gt; it is less than 10 % of the total volume of methane believed to be locked up in the East Siberian Sea sediments. They used the PAGE09 integrated assessment model, to quantify the effects of a major pulse of Arctic methane on the global economy, as it allows the extra emissions to be traced through sea level changes, regional temperatures, and regional and global impacts, such as flooding, health and extreme weather, as well as taking account of uncertainty (Hope, 2013). PAGE09 calculates the amount by which the Net Present Value (NPV) of impacts, which is aggregated between the present and 2200, increases for 1 more tonne of CO2 that is emitted, Which Wadhams says is effectively the social cost of CO2. PAGE09 is the most recent version of the model PAGE, Which had been developed by Chris Hope at the Judge Institute in Cambridge and was used by the Stern Review of the Economics of Climate Change to calculate the impacts of climate change (Stern, 2006). All of these results are based on 10,000 runs of the model, which allows for a full picture of the risks to be built up in order to work out the uncertainties.

Wadhams et al. tested 2 standard emission scenarios. For the ‘business as usual’ scenario it was assumed the world carries on along its present course releasing increasing emissions of CO2 and other greenhouse gases year after year with no mitigating actions. For the ‘low emissions’ case, with a 50 % chance of keeping the rise of the global mean temperature to less than 2oC (the ‘2016r5low’ scenario from the UK Meteorological Office), was run. With both cases releasing a decade-long pulse of 50 Gt of methane to the atmosphere between 2015 and 2025. The impacts of later, longer lasting or smaller pulses of methane were also explored.

The extra rise in temperature by 2040 resulting from the methane was 0.6oC, which is a substantial extra contribution. Wadhams says this would be catastrophic, in part as it is so rapid. All other global warming effects would increase in speed as a result and nothing could be done to shut off the methane short of cooling the water column to bring back the ice, which is very difficult to imagine how this could be achieved. The time at which the global mean temperature increase exceeded 2oC above pre-industrial levels would be brought forward by between 15 and 35 years to 2035 for the ‘business as usual’ scenario or 2040 for the low emissions scenario. Note how rapidly the climatic effect is generated by the methane, because a rise of 0.3-0.4oC occurs within a few years, though the peak of 0.6oC is reached 25 years after the beginning of the emissions.

The cost of this increase totals 60 trillion dollars over a century for the business as usual scenario, measured at present values. Wadhams says they had anticipated the cost of changes to the Arctic would be steep, in spite of economic gains in the short term for Arctic nations and some industries, though didn’t expect the magnitude of the cost they discovered. The amount is 15 % of the total of $400 trillion that has been estimated for all climate change impacts around the world over the same period, estimated by the same model. There will still be a cost of an extra $37 trillion for the low emissions scenario. Whether or not the pulse of methane is delayed by up to 20 years, only kicking in at 2035 instead of 2015, the costs are the same, or stretched out over 2 or 3 decades instead of 1 decade. There is almost exactly half the impact of a 50 Gt pulse of methane for a 25 Gt of methane. In order to model where change would result the model divides the Earth into 8 regions. The global distribution of the extra impacts closely mirrors the total impacts of climate change: with 80 % of the extra impacts by value in the poorer economies of Africa, Asia and South America. The extra methane emissions magnify all the impacts such as inundation of low-lying areas, extreme heat stress, droughts and storms. It has now been found that what was believed to be a purely Arctic effect, by the retreat of sea ice over Arctic shelves that was triggered by global warming, has a global impact. As Wadhams says that as usual it is the poor around the globe who will feel the effects of climate change the most.

Sources & Further reading

  1. Wadhams, P., 2016, A Farewell to Ice, Penguin Books Ltd.


Author: M. H. Monroe
Last updated:  17/09/2016
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