Of the top of my head, asteroids, bio weapons, disease, the Sun, AI and authoritarianism are more serious. Especially AI - not being the dominate species anymore will be dangerous. But 10°C more? That just requires AC and migration.
There are a lot of reasons such as whether food or water scarcity might trigger nuclear war. But the biggest reason is that it puts us into the territory of previous mass extinction events on Earth. This article does a good job of illustrating the worst possible outcome. It does belong up with the others on the existential threat scale.
http://burro.case.edu/Academics/USNA229/impactfromthedeep.pd...
Give it a read and let me know if you think industrial civilization could adapt to these conditions.
2) We are probably already in a mass extinction event. That also has little change of causing human extinction - we're the most adaptable species this planet has ever seen.
"known colloquially as the Great Dying... approximately 252 million years ago. It is the Earth's most severe known extinction event, with up to 96% of all marine species and 70% of terrestrial vertebrate species becoming extinct."
Seriously, it's a good article and quite short. I think you'd find it interesting food for thought and I'm honestly interested to hear your response to it, not some cheap dismissals.
Edit: if you really don't have time to read the whole thing, at least let me know what you think of the figure on page 6
Just look how poorly rich countries are reacting to the current levels of migration from less rich countries.
I was responding more to the callous nature of your comment than whether or not current warming trends are an absolute existential threat.
Plants, rainfall, and harvests are susceptible to changes in climate.
Globally, though, I'd be surprised if we could last a single year if every food crop failed. You can already see what this looks like in Africa and the Middle East - famine affects entire countries at a time. Imagine if there was a string of bad years - say 10 or 15.
As a kind-of related example, most of the US would starve within a week if there were no oil to power trucks. Our current globalized food production/transportation network is extremely fragile.