According to Dr. Peter D. Ward in Under a Green Sky: Global Warming, the Mass Extinctions of the Past, and What They Can Tell Us About Our Future one of the great mass extinctions of the past was triggered by global warming stopping the ocean conveyor (large ocean currents). The oceans stagnated and gave off hydrogen sulphide, (a gas more toxic than hydrogen cyanide) in such massive quantities that it killed off 90% of all life on earth, both plants and animals.
~ Roedy (born: 1948-02-04 age: 61)