Unfortunately, we may need to grow gills in a hurry.  Better hurry up with those genetic modification experiments.

During the end of the Permian era 250 million years ago, global warming ran rampant on Earth, extinguishing 95 percent of life in the ocean, and 70 percent of life on land.

Through the darkest days, the planet was a barren wasteland. Ocean circulation, so vital to our modern climate, had shut off. Huge algal blooms sucked the seas dry of oxygen. Poisonous hydrogen sulfide built up to lethal concentrations in the water and may have even been belched into the atmosphere, suffocating organisms on shore.

Where Life Found Refuge During Mass Extinction : Discovery News