LE BOURGET (France): Nearly 200 nations adopted on Saturday a global pact to fight climate change, calling on the world to collectively cut and then eliminate greenhouse gas pollution but imposing no sanctions on countries that don’t.

Loud applause erupted in the conference hall after French Foreign Minister Laurent Fabius gavelled the agreement. “This is huge,” tweeted US President Barack Obama. “Almost every country in the world just signed on to the #ParisAgreement on climate change....”

In the pact, the countries committed to limiting the amount of greenhouse gases emitted by human activity to the same levels that trees, soil and oceans could absorb naturally, beginning at some point between 2050 and 2100.

In practical terms, achieving that goal means the world would have to stop emitting greenhouse gases altogether in the next half-century, scientists say. Achieving such a reduction in emissions would involve a complete transformation of how people get energy, and many activists worry that despite the pledges, countries are not ready to make such profound and costly changes.