[wizzwizz4]

> Climate change is easy to solve: build fusion reactors which are 50x cheaper per kW to deploy than solar.

That just kicks the can down the road. If our general strategy (aim for exponential growth in all things) remains the same, cheaper power will mean we use more of it. Even if we completely phase out CO₂-releasing energy sources, the waste heat of our industrial processes would eventually dominate the power received from the sun. Even if we solve that… deuterium, like oil, is non-renewable. Doesn't matter how cheap it is: there are only two dozen trillion tonnes of it in the ocean, and once we've run out, we've run out.

[tbrownaw]

At some point the sun is supposed to go red giant and eat the earth. Anything that can last at least that long is effectively unlimited.

[wizzwizz4]

Projected oil demand is currently measured in trillions of tonnes per century. Deuterium is only seven or eight orders of magnitude more energy-dense than oil. If our power use continues to grow exponentially, we won't get close to the five billion year mark before running out: ten thousand years would be pushing it.