None of those would strike me as likely. Methane hydrate disaster would follow extended and very severe global warming. So far, the world has warmed only 0.8C on average. To get to methane hydrate disaster would require something massively greater, and that would require total mismanagement of future economies. Not likely, since we are already beginning measures to limit global warming.
I don't know how much of my prior posts about this "switch to Earth's hot stable state" (high pressure steam atmosphere at the surface) you read but your reply indicates you missed the main point, if you read them. So I quickly summarize it (for others also).
No we are NOT now limiting the process that could make the switch - we are not even slowing the currently increasing rate of releases of CO2. Slowly increasing concentration of CO2 in the air to even a factor of three times the current level is not a serious problem, will not make Earth sterile, as it has been at least that high in the past. It is the UN-PRECIDENTED and increasing RATE of CO2 release that could be a serious problem.
Methane, CH4, is about 15 times stronger IR absorber than CO2; however, CH4 is oxidized and destroyed in the air. (I forget half life, a few months now, I think. It depends upon many things. Currently the OH radical is used in the oxidation / destruction / process but the supply of that is produced very high up in the atmosphere by harsh UV splitting water and in the lower atmosphere OH can be exhausted. (For each CH4 molecule destroyed, an OH is destroyed too as it, with an H from CH4, becomes H2O.) If the CH4 concentration were to became equal to that CO2 has now, then the CH4 half life would become years, instead of months.
Current rate of global warming (due to current rate of CO2 release) and man’s activities (even trash dump and the huge cattle herds) that are releasing CH4 and with the CO2 are releasing now naturally stored CH4 from the hydrates and the CH4 simply dissolved in deep, previously-frozen lakes, especially those in Arctic plus the now melting permma frost, bogs, etc. so that the total CH4 release rate is already significantly greater than the destruction rate. Proof: CH4 atmospheric concentration is growing, percentage wise, more rapidly than CO2’s rate of increase.
I.e. we already have a positive feedback system, but the loop gain is currently less than unity. BUT the loop gain could become greater than unity if the atmospheric life time of CH4 were to increase as it would if the rate of OH being delivered down to the lower atmosphere were less than the rate of CH4 being released from the surface.
I.e. too rapid CH4 release flux can overwhelm the lower atmosphere's OH and make the atmospheric life time of CH4 become years, not months. Then with greater than unity feedback loop gain the temperature begins to rise on an exponential growth curve.
All exponential growths eventually saturate and stabilize. If this one is stabilized by exhausting the stored CH4 then that, rather than the tropical ocean surfaces starting to boil, could occur but most estimates say there is more carbon in CH4 stored than all the carbon stored in coal and oil. If the oceans start to boil, or even if the air temperature becomes too hot for water vapor to fall from the sky as rain, then the exponential temperature rise accelerates as the lower layer of the air become mainly water vapor. (Water vapor is a much better absorber of the IR trying to escape from Earth’s surface than even CH4 is).
SUMMARY: afaik, NO ONE CAN SAY
WITH CERTAINTY THAT EARTH IS NOT ALREADY IN THE EARLY STAGES OF SWITCHING TO ITS HOT STABLE STATE. (This due to the un-precedented RATE of CO2 release, not due to the level of CO2) For other reasons, Venus switched from an Earth like state to its hot stable state some millions of years ago. I.e. any lead on the surface of Venus is liquid. If Earth switches, the oceans will eventually boil away into space and then, when the water vapor is gone and there is no more CH4 to release, the surface temperature will rapidly (a few thousand years) drop - perhaps down to only about 250F and then over many thousand of years may become even cooler than it is today (if it no longer has an atmosphere).
The release of an inimical life form seems unlikely to be extinction level disaster. A virus or similar might wreak havoc, and kill a billion people, but humans are very capable, and will engage remedial action.
Please suggest what mankind could do if in 200 years some deranged but brilliant scientist makes a piron in his garage that is:
Wind born, enters leaves it falls on, and in the process of replicating its self 100 times inside EACH leaf, kills the leaf and plant (for example by interfering with the photosynthesis process). I think that all life would die in a few years, except possibly some ocean creatures if his piron cannot attack photo plankton. For example, if the piron only enters leaves via their stoma (where the CO2 enters) which AFAIK photo plankton do not have. Piron molecules, although only single molecules, may be too big to diffuse thru the cell wall as the CO2 does, I think, in photo plankton. Compared to making the DNA for living cell (already done) making a much smaller piron molecule is very easy. - Not yet a one man job in his garage, but wait 200 or less years and it will be.
Would mankind try to collect every leaf on Earth, food crops included, and burn it? Or try to stop the wind? Again: Please suggest what mankind could do.
Top get back on thread, If you want mankind to be able to survived for next million years, I suggest decreasing his intelligence to that of a turtle - they have made it about a million years, I think.
. I don’t think I’m that special either, the world can survive without my descendance.
