15 years is probably too extreme for even the most pessimistic climate change scenarios where you get to the point of boiling the oceans.

However, these kids will be dealing with the consequences of extreme climate change in their lifetimes. Lots of people are going to die. Some societies will collapse. It's not going to be easy and having the world leaders today range from offering emotional support and no effective policy decisions to outright hostile to the entire concept of climate change is not helpful.

Human beings haven't relied on "the food chain" for thousands of years, but it's certainly true that climate change will have a big impact on agriculture, the recent IPCC report on land covers the topic in some depth[1]. Models of runaway change don't suggest humans would be wiped out (though I wouldn't want to live near a coastline...[2]), especially not within 15 years.

1: https://en.wikipedia.org/wiki/Special_Report_on_Climate_Chan...

2: https://www.pnas.org/content/115/33/8252

And how likely are either of these?

The carbon locked up in fossil fuels and a lot of sedimentary rocks was in the atmosphere at some point. Granted the sun was a bit cooler, but the earth has been drastically warmer in the past and life went on just fine. We have the technology today to grow all of our food in hydroponic greenhouses in Siberia and Canada, but food is so cheap that nobody is bothering to.

If we put a lot of effort on removing carbon from stable minerals, there is probably enough of it on Earth's crust to make it uninhabitable. But that's a large engineering effort that I don't think humanity is currently able to achieve.

Climate what now? /s

For real though I swear half of hacker news must work in oil and gas.