An Earth six degrees warmer than today would have sea levels as much as 200 metres higher than they presently are with the oceans themselves too warm to sustain much life. This world would be almost entirely covered by desert, with only today’s polar regions capable of supporting extensive agriculture. Yet even all of these challenges would be trivial compared to the real game-changer: substantially increased levels of atmospheric methane. In that event, anything with lungs would struggle to breathe.
