Is the arctic carbon bomb about to go off?

• Author: Berger, John J.
• Position: Ecology

THE GLOBAL CLIMATE system is comprised of major components or elements. At the largest scale, these include the atmosphere (vapor), cryosphere (snow and ice), hydrosphere (oceans and freshwater), geosphere (soil and rocks), and biosphere (living things). On a smaller scale, each of the major climate elements has key components that themselves can exert powerful impacts on global climate. For example, permafrost--thick subsurface layer of soil that remains frozen year-round--and frozen methane deposits in the seabed, known as methane hydrates or clathrates, are critically important parts of the cryosphere and hence the climate system.

When an element becomes unstable, it not only can accelerate climate change, but potentially can cause a chain reaction consisting of an irreversible, self-intensifying cycle. A global climate element close to one of these dangerously unstable conditions is said to be at a tipping point. At that juncture, an incremental change in climate conditions can provoke a disproportionately large and dramatic feedback response that permanently could disrupt the world's climate. If the feedback is a warming, that warming will cause additional warming in a continuous, positive feedback cycle. A polar icecap or region of permafrost close to its melting point is at a tipping point.

Tipping points are not reversible on time scales of interest to current generations. A climate threshold leading to a tipping point thus is a little like the spring-loaded steel spikes at a parking lot exit. You can roll forward over them, but you cannot back up. Similarly, passing that threshold is a one-way journey that leaves our climate at the mercy of self-reinforcing natural processes.

When the Arctic permafrost tipping point or climate threshold has been passed, the permafrost begins to deliver ever-increasing amounts of heat-trapping gases to the atmosphere in response to global warming. The additional heat-trapping gas then generates additional warming in a vicious, self-amplifying cycle. Eventually this significantly could reduce the planet's ability to support human life.

By 2100, average global temperatures will be warmer than at any time in the past 5,000,000 years, if current emissions trends continue. However, as global temperatures rise, more and more extensive areas of permafrost and methane hydrates will begin thawing, as average increases in global temperature are magnified in the Arctic.

When we warm the planet, we do likewise...