| I'm worried that this could be just 'the tip of the iceberg' [1]. I have a suspicion that even J. Hansen is still underestimating the issue. Just looking at [2] the variability of current estimates of stored methane is enormous - going from 10E2 to 5x10E4 Gigatonnes! Methane does greenhouse forcing 20-25x as strong as CO2 over 100 years, or as much as ~160x if you only count 10 years. Depending on how fast methane gets released this really matters - if the released methane triggers more methane to come out through warming we may be in big trouble, even without burning all coal, oil and gas reserves currently known. Further reading concerning methane: [3], [4]. Reason why dismissing this using PETM boundary is probably invalid: There was with high certainty less methane around since PETM didn't immediately follow a cold high-storage period, solar energy was also weaker, and most importantly, PETM was caused by methane alone, not a combination of fossil fuel burning in addition to methane [5]. Just to clarify: If we get the effects of PETM alone, this means around +8C global average on top of what we're doing. But from what I'm reading, PETM effects are not the whole story as pointed out above. Not that it really matters, +10-12C global average is almost certainly a global killer alone (except bacteria), it's just that I don't think it would stabilise there, it would go on to pressure cook earth's surface until absolutely nothing is left. This stuff has me worried by far the most, especially for my now 2yo son. [1] https://www.kairoscanada.org/wp-content/uploads/2011/12/PBP2... [2] http://oceanrep.geomar.de/30683/1/GasHydrates_Vol1_screen.pd... [3] https://www.sciencedirect.com/science/article/pii/S187661021... [4] http://science.sciencemag.org/content/327/5970/1246 [5] http://www.columbia.edu/~jeh1/mailings/2013/20130415_Exagger... |
The earth will one day reach a true runaway greenhouse when the sun brightens by 10% in about 1.1 billion years. But according to J. Hansen in 2013 a complete greenhouse runaway can't happen unless the high temperatures are maintained for several million years, long enough for all the oceans to evaporate, and our own forcing will only(!) last a few tens of thousands. So my understanding is that we won't cause all life to go extinct, if that makes you feel any better.