Has climate change tipped out of control?

As part of the Global Risks Report 2013, the World Economic Forum’s Risk Response Network has identified five “X Factor” risks in partnership with Nature. These look beyond mainstream risks to five emerging potential game-changers.

The threat of climate change is well known. But have we passed the point of no return? What if we have already triggered a runaway chain reaction that is rapidly tipping Earth’s atmosphere into an inhospitable state?

The natural greenhouse effect is a prerequisite for life. Without it, the Earth’s global average surface temperature would be far below zero. But our planet’s climate is a volatile beast. Small fluctuations in the Earth’s orbit around the sun can exert a major influence on our climate. So can the varying concentration in the Earth’s atmosphere of heat-trapping molecules such as carbon dioxide, to which we have been adding through greenhouse gas emissions.

How pronounced and how fast the warming will be (and how it will affect rainfall and storminess) is hard to say as even the most sophisticated computer models cannot capture all the factors involved in a system as complex as the Earth. But it could be more dramatic and difficult to adapt to than most scientists predict because of the natural feedbacks in the system, linked to processes in the oceans and on land.They have the potential to amplify climate change to a point of fundamentally disrupting the global system. The much debated questions are where these tipping points lie, how soon they might be reached, whether they can be predicted – and what will happen when they are crossed.

The perhaps best-known positive feedback mechanism is the so-called ice-albedo feedback. In a warmer world there will be less snow and sea ice. Their melting reveals the darker land and water surfaces below, which absorb more solar heat. More absorption then causes yet more melting and warming, and so forth, in a self-reinforcing feedback loop. The unprecedented thawing of 97% of Greenland’s surface ice in July 2012, for example, has led to a darkening of Greenland’s ice cap, meaning that it will begin to absorb higher levels of solar energy and melt faster still.

Melting of the complete Arctic summer sea ice – the Arctic is expected to be seasonally ice-free by around 2040 – could probably be reversed on human timescales if greenhouse gases are reduced and temperature drops. But if the several kilometre-thick ice sheets that cover Greenland and Antarctica dwindle, they may not so easily reappear in a cooler world. New ice would have to form at low elevations, where temperatures are higher.

Permafrost melting, land use and vegetation changes, and the effects of changing cloud cover provide for other major feedback mechanisms. Some scientists suspect that by 2040 up to 63 billion extra tonnes of carbon – and up to 380 billion tonnes by 2100 – might be released by the thaw and degradation of permafrost soil alone.

Finally, there is the potentially huge feedback effect of water vapour, a natural greenhouse gas in itself. A warmer atmosphere can hold more water. As the average air temperature soars in response to our burning of fossil fuels, evaporation and atmospheric concentration of water vapour will increase, further intensifying the greenhouse effect. On Venus, this probably caused a runaway greenhouse effect, which boiled away the oceans that may have existed in the planet’s early history.

Luckily, man-made climate warming has virtually no chance of producing a runaway greenhouse effect analogous to that of Venus. Even so, scientists with the Intergovernmental Panel on Climate Change (IPCC) assert that the water vapour feedback on Earth could be strong enough to double the greenhouse effect due to the added carbon dioxide alone.

While climate change debates of the past decade centred on whether or not humans could be responsible for altering a system as great as Earth’s climate, we may be rapidly moving into forced discussions on how best to strengthen resilience and adaptive capacity to cope as Earth’s climate auto-pilot mercilessly hurtles us towards a new and unknown equilibrium.

See also: X Factors: The risks that bite back, by Tim Appenzeller

Image: Splinters of ice peel off from one of the sides of a glacier in Argentina REUTERS/STRINGER Argentina