This is something that our sector has spent much time grappling with. It is what we are still trying to work out

Barack Obama’s negotiators make their debut at UN climate talks on Sunday, but many nations have rowed back on plans, focusing instead on the economy.

Governments broadly support tough 2050 goals for cuts in greenhouse gas emissions but are split on how to share out the reductions.

The world could eliminate fossil fuel use by 2090 by spending trillions of dollars on a renewable energy revolution.

Backers of technologies to curb global warming advocate dumping iron dust into the seas or placing smoke and mirrors in the sky to dim the sun.