An anonymous poster asked about possible human extinction caused by acidification of the oceans. I believe I answered him reasonably well enough why I think that ocean acidification is unlikely to cause an extinction.
That said I did some reading about "anoxic events" and extinction events etc and the big one appears to be the K-T exinction where more than 90% of the world's species went extinct over a period of a couple million years.
Here's what's interesting:
There was at least one and probably many comet impacts during this period combined with a long (half a million years) period of volcanic eruptions.
What's interesting about this is that the food chain collapsed.
Well if we ask what that means it's the following: photosynthetic plants perished in great numbers during this period.
Sounds like "the road"!!!
If we ask ourselves what could cause this then we loop back and take a look at what actually happened then maybe we can draw some conclusions.
So first of all: what would cause photosynthesis to decline?
Well the most obvious answer is if the amount of sunlight went down.
That obviously didn't happen, since the Sun isn't very variable, so what else could have caused it?
Possibly massive plagues on plants or something blocking the ability of plants to use the available sunlight.
We don't have any evidence of any plagues on plants but comet impacts and volcanoes both throw huge amounts of dust into the atmosphere. We have evidence for both comet impacts and a long (half a million years) period of intense volcanic activity.
So maybe during this period the available sunlight was severely blocked by dust?
If that happened again I'd have no problem believing in "the road" type scenarios being in our future, but the situation we have isn't analagous. In fact it's more analagous to suddenly turning up the thermostat with the same amount of sunlight getting in.
The evidence suggests that plants do better with more heat so we're unlikely to see a collapse in photosynthesis on land. In the oceans we could see some issues for deepwater organisms and carbonate shelled organisms due to acidification (yet there's also evidence for foraminfera during super greenhouse events so clearly they don't ALL die out).
On balance it's hard to say what would happen without all the dust being injected into the atmosphere concurrently with carbon dioxide as happened during the K-T extinction event. I suspect there would be winners and there would be losers.
Animals on land did better during the K-T event. Although many died (primarily herbivorous animals), omnivores and detritus eaters did well.
I also suspect (call it anthropocentric arrogance if you like) that we would survive even a dust+carbon dioxide catastrophe given that we are omnivores and very very inventive, but carbon dioxide and global warming alone are not going to cut it to wipe us out.
Civilization itself is also pretty resilient as long as there is enough sunlight to grow crops. Some extreme doomers have said that the human species has never had to pass through a climate as warm as the super greenhouse climate of the cretaceous. I beg to differ. Saudi Arabia regularly reaches temperatures of 50C which is ridiculously hot, yet civilization continues there quite happily, though they depend heavily on technology and also on trade, similar to Las Vegas. Given that Canada, Siberia and Greenland would become productive farmland at the expense of other regions which warmed up too much to continue to be as productive agriculturally as they are now*, the losing regions would have to depend on trade, but technology would allow them to continue to survive. Las Vegas is damn hot for example and it survives on trade, thought the ecologists would say it's "unsustainable".
*Astute readers may note the apparent contradiction that plants like more heat with the fact that beyond a certain point, raised temperatures start to cause declines in agricultural production. The reason for this is that as it gets hotter, there is more and more evaporation and while the total quantity of water remains the same and plants are able to continue to photosynthesize, the plants aren't able to access the water because it's in the air instead of the soil. The solution to that particular problem is rainforests which are able to hold on to and regulate the water cycle more efficiently than we can in hotter regions. What that implies is the shift of agriculture to higher latitudes. Luckily, however we have tons of land up north.
Returning to the question of whether human civilization is robust at higher temperatures versus the charge by the ecologists that the human *species* has never dealt with such high temperatures before even though we have proof right now that we have (the cities in hot regions):
If what the ecologists and doomers are really saying is that human beings unaided could not survive such extreme temperatures well duh. I've been arguing all along that our current population depends on technology and technology will be required to maintain our current population.
Additional greenhouse gases and increased temperatures will do nothing to affect our ability to continue to maintain our technological base. On the contrary, the greenhouse gas doomers are the ones demanding the shutdown of our economy and the collapse of our technological base.
In fact the cut back solution is equivalent of pulling the rug out from under civilization if you examine the evidence of what actually DOES cause extinctions.
Shut down the economy and we're fucked.
Those who support that concept in order to reduce greenhouse gases are insane misanthropists nothing more nothing less.