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Methane (aka natural gas) is taking up a growing share of the world's supply of energy.
Last month a consortium of NGOs, including Greenpeace and 350.org, published an analysis of the investments now being planned. The Oil Change International report (good title that) tells us that the rich G20 countries are projected to spend more than US$1.6 trillion developing new gas fields over the next 12 years to 2030.
Just five countries - the US, Russia, Australia, China and Canada - are expected to make up three-quarters of that total. To these may now be added Argentina, where gas reserves are thought to be the second-largest in the world.
Methane does have significant advantages relative to coal as a source of heat, producing twice the heat per kilogram of anthracite coal, and four times the heat of the lignite coals that are used here in the South Island to produce milk powder. When burned, it does emit the CO2 that will be the major driver of global warming for centuries to come, but the rate of emissions is half that of burning oil. Hence methane is seen as a useful transition fuel away from the dirtier sources of carbon emissions while we develop alternative carbon-free energy sources.
The Oil Change report challenges some of this thinking. The companies making these massive new investments in natural gas will of course expect a return on their investment, and a gas field typically operates for 30 years or more to make that return. Hence these investment decisions, taken now, are locking us into ongoing emissions of CO2 and methane right up to 2050, when the Paris Agreement challenges us to eliminate all carbon emissions from the power sector. To meet that target, we need to be phasing out all sources of carbon over the next 30 years. The report also argues that wind and solar energy sources are already cheaper than gas in many parts of the world.
Much of the increase in gas supply is being won by fracking. Fracking is an aggressive way to get methane out of the ground in which significant volumes of raw methane are released straight to the atmosphere. And in the short term, raw methane is a far more powerful greenhouse gas than CO2.
I have already cited in these columns a study by Robert Howarth, of Cornell University, which recognises this high short-term warming potential of released methane and finds that, over the first 20 years, fracked shale gas is a stronger driver of global warming than oil, and even coal.
New Zealand's methane emissions come from a different source, as we all know. For us, it is agriculture, not energy supply, that challenges us to reduce our contribution to a warming planet. New Zealand is also unique for the importance of agricultural methane in its greenhouse gas emissions, making up nearly half the national total.
So it is important when the pre-eminent science journal Nature publishes a paper arguing that we need to distinguish between the methane that we extract from long geological storage under the ground - a fossil fuel - and the methane produced by ruminant animals.
The paper, published last month by authors including Prof Dave Frame, at Victoria University, in Wellington, points out that agricultural methane is one step in a closed chemical cycle in which grasses extract CO2 from the atmosphere, that animals eat, producing methane, which returns to the atmosphere and decays over a century or so back into CO2 again.
As such, it does nothing to add to the stock of CO2 already in the atmosphere, simply taking what is there and sending it back again. By contrast, burning fossil methane involves extracting gas that could stay safely locked up in geological structures and adding to the stock of atmospheric CO2.
This is surely an important insight and we should expect it to feature large in New Zealand's discussions with the rest of the world about our contributions to emissions control.
I am certainly not qualified to argue the science here, but I can imagine an argument or two that might be used against us. First, accepting that agricultural methane is merely cycling around CO2 already present in the atmosphere does not absolve us from a responsibility to help reduce the dangerously high stocks of atmospheric CO2 that will drive changes in the climate for centuries to come, and for us that means reducing agricultural methane.
Second, the conversion of CO2 into methane changes the time profile of the drivers of global warming, from the centuries over which CO2 will warm the planet and bringing them forward into our own lifetimes.
Over its first 100 years in the atmosphere, methane is 25 times more powerful as a greenhouse gas than CO2. Over its first 20 years, a whopping 86 times more powerful. Indeed, the rate at which several of the effects of a warming world are coming upon us continues to surprise science: the disappearance of Arctic summer ice; the melting of Greenland's glaciers (and our own); the destabilising of the West Antarctic ice sheet.
In a way, the conversion of CO2 into methane is bringing forward into our own times an enlarged picture of what atmospheric CO2 will be doing to the planet long after our generation is gone. And this may not be a bad thing if it gives us the stimulus we need to get carbon and its global-warming equivalents out of our lives by 2050.
Colin Campbell-Hunt is an emeritus professor at the CSAFE Centre for Sustainability, University of Otago. Each week in this column, one of a panel of writers addresses issues of sustainability.