It'll certainly be a stinky way to go. You've smelled it before, if you've ever rolled a rock over on a beach at low tide, smelled a propane leak, or suffered the consequences of eating jerusalem artichokes (aka "fartichokes") or a healthy serving of beans. It's hydrogen sulfide -- mother nature's cleanser of choice whenever the organisms on planet earth become too annoying, like us.
It happened before -- and is the cause of most previous mass extinctions in the geologic record. A warming planet stratifies the oceans, reducing circulation and oxygenation. Hydrogen sulfide producing bacteria start to dominate, releasing clouds of the toxic gas which wipe out most oxygen-breathing creatures.
Unfortunately for us, it's starting to happen again, because we think we "need" fossil fuels. A warming planet is slowing ocean currents, and our oceans are again stratifying, as the NE Pacific did during the recent El Nino that lead to droves of dead seabirds and marine mammals washing ashore from California to Alaska. This year the stratification is leading to the worst red-tides ever seen in Chile, prompting the shutdown of Chile's fishing fleets.
Off the coast of Namibia, the hydrogen sulfide producing bacteria bloom in quantities that are visible from space. Current modeling suggests that most of the world's oceans will be significantly stratified by the 2030s, leading to the conditions that would allow hydrogen sulfide producing bacteria to flourish.
We've already bleached out 95% of the northern great barrier reef this year, and recently discovered that the coral reefs of the Florida keys are now dissolving in the CO2 acidified sea water. The crazed hippies at the USGS suggest that we may well see the first-ever blue-sea event in the arctic this year, as the north polar icecap disappears for the first time in human history. If the icecap goes, all the methane under the arctic sea comes out, and our problems become a whole lot tougher to solve. What will next year bring?
Driven a car lately? Flown anywhere? Turned on your (fracked) gas furnace? Do we need these things more than we want our kids to survive? It's long past time to remember how to live as we did before.