The non-binding accord, which the US reached with key nations including China and Brazil, "recognises" the scientific case for keeping temperature rises to no more than 2C but does not contain commitments to emissions reductions to achieve that goal.
US officials spun the deal as a "meaningful agreement" but even Barack Obama said: "This progress is not enough.
"We have come a long way, but we have much further to go."
It is up to national parliaments to adopt the accord, after which signatories will be obliged to take measures to reduce greenhouse gas emissions and start preparing to help poor countries adapt to climate change. The intention is for a full legal agreement to be signed within a year.