Time to hit the panic button: time is running out to prevent a climate catastrophe.

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

SINCE THE START of the Industrial Revolution, humans have released 545,000,000,000 metric tons of carbon into the atmosphere. We now have more airborne heat-trapping gases--carbon dioxide, methane, and nitrous oxide--than at any time in the past 800,000 years. We are putting about 10,500,000,000 metric tons of carbon a year into the air. Annual emissions of carbon dioxide--from fossil fuel burning and cement production plus land-use changes--surged 54% from 1990-2011.

The average land and sea temperature has risen by about 1.5[degrees]F since the mid 19th century. The Greenland and Antarctic Ice Sheets are melting at increasing rates, as are the world's glaciers. Positive climate system feedbacks--warming that inexorably leads to more warming--are appearing, such as the warming, melting, and thinning of carbon-rich frozen soils known as permafrost. Arctic sea ice is melting very quickly as well, adding still more positive feedback. Sea levels are rising at an accelerating rate. Ocean temperature, currents, and salinity are changing. The oceans are growing dangerously more acidic. Because global temperature has risen, heat waves and other weather extremes have become more common. The onset of seasons has altered. The global water cycle and atmospheric circulation have been affected negatively.

These trends are likely to continue and accelerate for the foreseeable future but, even should emissions stop, adverse climate effects will continue for millennia. The greater cumulative emissions become, the higher the Earth's final temperature, and the more severe the consequences--longer-lasting droughts, more insufferable heat, larger deserts, scarcer food and water, higher oceans, more corrosive seawater, more fetid ocean bottoms, and a paroxysm of species extinctions.

The Earth cannot withstand the ravages of habitat destruction indefinitely, nor the strain of an exploding human population and abrupt climate change. Healthy natural ecosystems will lose their diversity or collapse outright. As their productivity declines, so will the Earth's life-support capacity. People will suffer. Vulnerable populations will begin to contract. Even if heat-trapping gas emissions magically fell to zero tomorrow, the atmosphere still would get another one to two degrees hotter, just from excess heat already absorbed by the oceans.

In a matter of decades, billions of people will lack adequate food and water if society continues on its current irresponsible emissions trajectory. Governments and relief organizations already are struggling to care for millions of refugees. In an overheated world, tens of millions...