Carbon Feedback Cycles

As we continue to pump large amounts of carbon into the atmosphere, the rising concentrations will lead to an ever greater amount of heating and general climate change. The threats from global warming are very serious and require urgent action. However, if we fail to reach a strong agreement at Copenhagen, the danger is not just that carbon levels will continue to rise, leading to a linear increase in environmental harm. Instead as carbon levels rise, various positive feedbacks may kick in, accelerating the process of climate change.

A study in Nature mentions that soil, globally, contains about 300 times the carbon we are currently releasing annually into the atmosphere. This was previously assumed to be inert and unchanging. After a systematic survey of 6000 sites in the UK, however, the data showed a significant amount of soil organic carbon being released from the soil. The total loss for the UK is estimated at 13 million tons a year, enough to completely offset all emissions reductions made by the UK under the Kyoto Accord.

The study doesn't arrive at a conclusive explanation for the cause of this release of carbon from the soil. They speculate that several factors are involved, including warming temperatures and changing land use. The conclusion is that this needs more study, and the release of carbon from the soil needs to be taken into account in efforts and agreements designed to prevent climate change. Clearly, if this factor can completely offset reductions made under Kyoto, we are going to need tougher targets, as well as potentially other changes in our land use and farming methods.

A feedback cycle is also involved in the case of melting ice. There are vast quantities of ice and snow in the polar regions as well as in glaciers and on mountain tops. Ice and snow reflect a large amount of the heat radiated by the sun. Rising carbon levels mean that more and more of this heat is trapped by the atmosphere and radiated back to the Earth. As this causes temperatures to increase, more and more ice melts, exposing either land or the surface of the sea. Both land and the sea absorb much more heat than snow or ice, resulting in faster warming of the planet.

This phenomenon is called Ice-albedo feedback, and it means that as the planet gets warmer, it absorbs more heat, leading to more melting, and so on. This cycle results not only in an acceleration of global warming, but could also lead to an acceleration in sea level rise and the loss of glaciers. This is bad news for the Tibetan Plateau and other areas dependant on outflows from glaciers.

Another potential feedback source is the vast deposits of methane stored in permafrost in northern Russia, Europe and Canada. There is estimated to be about 70 billion tons of methane stored within the permafrost. As temperatures rise, many areas of permafrost are beginning to melt and release methane into the atmosphere. Methane is a greenhouse gas, like carbon dioxide, but is roughly eight times more potent. An increase in atmospheric concentrations of methane could accelerate warming, which would, of course, speed up the melting of permafrost, releasing yet more methane into the atmosphere at an increasing rate.

The world's oceans currently absorb about 40 percent of our carbon emissions. While this is causing ocean acidification and other problems, there is another area of concern. A new study has shown that as temperatures rise, the ocean is losing its ability to absorb carbon dioxide. Of course, this means that more carbon will stay in the atmosphere, leading to more warming, and faster heating of the oceans, in another feedback cycle.

These and other feedback effects may be one of the reasons why the impacts of climate change are happening at a much faster rate than predicted by scientists and the IPCC. Previous predictions appear to have been too conservative, and we are now on track, in many cases, for what were previously considered worse-case scenarios. This makes it even more important that we reach a strong agreement at Copenhagen, and it means we must set much tougher emissions targets as soon as possible.