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‘Compost bomb’ is latest climate change ‘tipping point’

By Louise Gray (The Telegraph) - March 27, 2012

Climate change could fuel a giant ‘compost bomb’, scientists have warned, as decaying vegetation stuck under under the ice or in peat bogs starts to heat up and tips the world into dangerous global warming.

In gardens every spring compost heaps are beginning to warm up as the microbes in the soil get to work breaking down vegetable matter and releasing a certain amount of greenhouse gases – as well as a pungent smell.

This process is repeated on a much larger scale when microbes trapped in the permafrost in the Arctic, tropical swamps or peat bogs around Europe and the UK heat up.

Scientists fear that if temperatures warm up too fast it will destabilise these natural cycles and unlock billions of tonnes of greenhouse gases into the atmosphere.

Peatlands cover just 3 percent of the world’s land area, but the soil could store up to twice the amount of carbons currently in the atmosphere.

Peter Cox, Professor of Climate System Dynamics at the University of Exeter, explained the process of decomposition kicked off by warmer temperatures.

He said microbes in the soil generate more heat as they break down vegetable matter, releasing a certain amount of gases until the “compost heap” is exhausted or temperatures cool

However if temperatures rise too fast there is a “runaway effect” as the microbes are producing heat so fast it cannot be released and builds up, potentially causing fires. Gases also build up eventually causing a huge ‘burp’ or explosive release of carbon into the atmosphere all at once.

“If you put your hand to a compost heap it is warm,” he said. “It is exactly what is happening in peat soils around the world as organic matter breaks down.

“Normally it does not matter as carbon dioxide and other gases are released gradually into the atmosphere.

“But if we are warming the planet too fast then theoretically the soils will warm up like a compost heap, making the microbes work faster and generate yet more heat. This causes heat and gases to build up and an abrupt release of carbon into the atmosphere.”

The compost bomb also causes a positive ‘feedback loop’ as the hotter the soil gets the harder the microbes work, causing yet more heat. Also the gases released cause more global warming.

Speaking at the Planet under Pressure conference in London, Prof Will Steffen, a global change expert from the Australian National University, described the ‘compost bomb’ as one of many “tipping points” in danger of pushing global temperatures beyond dangerous levels.

Almost 3,000 scientists are attending the conference to discuss the threats of global warming and the best way forward.

He said that there is evidence of a ‘compost bomb’ around 55 million years ago that caused a huge amount of carbon to be released into the atmosphere all at once.

Scientists are also investigating whether a ‘compost bomb’ caused the peatland fires around Moscow a couple of years ago.

“We know how the compost bomb process works, we think we have seen it in the past, we just do not know what global warming will trigger it or when it will happen, ” he said.

Other tipping points identified by Prof Steffen as part of the ‘great acceleration’ in global warming include the melting of ice in the Arctic that creates more areas of ocean and therefore absorbs more heat than reflective white, again causing a positive feedback loop.

Although the global population is stabilising and we are more efficient at producing energy, human beings are causing more carbon dioxide to be released than ever before because the amount individuals consume is still rising, causing a number of environmental impacts.

Prof Steffen said that this period of climate change caused by humans, known as the ‘anthropocene era’, could ultimately cause the whole system of ice ages followed by warm periods, that has allowed life on Earth to flourish, to be over.

“The further and faster we push temperatures up, the more serious the risks,” he said. “But we simply do not know where these tipping points lie.”