The importance of avoiding the “Tipping Point” in the climate system
Global warming so far, about two degrees Fahrenheit over land areas, seems almost innocuous, being less than day-to-day weather fluctuations, said Dr. James Hansen, director of NASA’s Goddard Institute for Space Studies, speaking at the 2008 Kansas Wind & Renewable Energy Conference in Topeka. But more warming is already “in the pipeline,” delayed only by the great inertia of the world oceans. And the climate is nearing a dangerous tipping point, Hansen warned.
A tipping point in the climate system occurs when there are large, ready positive (amplifying) feedbacks, such as Arctic sea ice, West Antarctic and Greenland ice sheets, and frozen methane hydrates, he said. These feedbacks can partner with the inertia of the oceans and ice sheets to create a situation in which the warming in the pipeline, due to human-made greenhouse gases (GHGs) already in the air, can carry climate to large rapid changes without any additional forcing.
Another critical fact is the long lifetime of fossil fuel CO2 emissions, Hansen pointed out. “Half of a fossil fuel CO2 pulse disappears within 20-30 years, mostly into the ocean. However, much of the CO2, about one-fifth, is still in the air after 1,000 years,” he said.
Climate can reach points such that amplifying feedbacks spur large rapid changes. “Arctic sea ice is a current example. Global warming initiated sea ice melt, exposing darker ocean that absorbs more sunlight, melting more ice. As a result, even without any additional greenhouse gases, the Arctic soon will be ice-free in the summer,” Hansen said.
More ominous tipping points loom, he added. “West Antarctic and Greenland ice sheets are vulnerable to even small additional warming. These two-mile-thick behemoths respond slowly at first, but if disintegration gets well underway it will become unstoppable. Debate among scientists is only about how much sea level would rise by a given date. In my opinion, if emissions follow a business-as-usual scenario, sea level rise of at least two meters is likely this century. Hundreds of millions of people would become refugees. No stable shoreline would be reestablished in any time frame that humanity can conceive,” he said.
Animal and plant species are already stressed by climate change, he noted. “Polar and alpine species will be pushed off the planet, if warming continues. Other species attempt to migrate, but as some are extinguished their interdependencies can cause ecosystem collapse. Mass extinctions, of more than half the species on the planet, have occurred several times when the Earth warmed as much as expected if greenhouse gases continue to increase. Biodiversity recovered, but it required hundreds of thousands of years,” he said.
-- Steve Watson, CASMGS Communications