The Kyoto Protocol requires that greenhouse gases be stabilized at a level that prevents

‘‘dangerous anthropogenic interference’’ with the climate system. In an effort to help define what this means, O’Neil and Oppenheimer (2002) relate certain physical effects to rising temperature:

● At 2 degrees Fahrenheit, we can expect ‘‘large-scale eradication of coral reef systems’’ on a global basis.

● At 4 degrees Fahrenheit, an irreversible process leading to the collapse of the West Antarctic Ice Sheet and a sea-level rise of 25 feet becomes significantly more likely.

● At 6 degrees Fahrenheit, the shutdown of the Gulf Stream leading to a sudden, dramatic cooling in Northern Europe and accelerated warming in the South Atlantic becomes significantly more likely.

The authors conclude that it is impossible to prevent a 2-degree warming. Based on the relationships above, they call for holding global temperature increases to less than 4 degrees.

a. Is this an efficiency, ecological sustainability, or safety standard? Why?