"As soaring greenhouse gas (GHG) emissions drove global CO2 concentrations past 400 parts per million in May 2013, shell-shocked climate scientists warned that unless we urgently adopt "radical" measures to suppress GHG emissions (50 percent cuts in emissions by 2020, 90 percent by 2050) we're headed for an average temperature rise of 3 degrees or 4 degrees Celsius before the end of the century.
"Four degrees might not seem like much, but make no mistake: Such an increase will be catastrophic for our species and most others. Humans have never experienced a rise of 4 degrees in average temperatures.
"But our ancestors experienced a four-degree cooler world. That was during the last ice age, the Wisconsin Stage (26,000 to 13,300 years ago). At that time, there were two miles of ice on top of where I'm sitting right now in New York City.
"In a four-degree warmer world "Heat waves of undreamt-of-ferocity will scorch the Earth's surface as the climate becomes hotter than anything humans have ever experienced. ... There will be "no ice at either pole." "Global warming of this magnitude would leave the whole planet without ice for the first time in nearly 40 million years." Sea levels will rise 25 meters - submerging Florida, Bangladesh, New York, Washington DC, London, Shanghai, the coastlines and cities where nearly half the world's people presently live.
"Freshwater aquifiers will dry up; snow caps and glaciers will evaporate - and with them, the rivers that feed the billions of Asia, South America and California. The "wholesale destruction of ecosystems" will bring on the collapse of agriculture around much of the world. "Russia's harsh cold will be a distant memory" as "temperatures in Europe will resemble the Middle East. ... The Sahara will have crossed the Strait of Gibraltar and be working its way north into the heart of Spain and Portugal. ...
"With food supplies crashing, humanity's grip on its future will become ever more tentative." Yet long before the temperature increase hits four degrees, the melting will have begun thawing the permafrost of the Arctic, releasing vast quantities of methane buried under the Arctic seas and the Siberian and North American tundra, accelerating GHG concentrations beyond any human power to stop runaway warming and sealing our fate as a species.(1)"