The BBC's environment correspondent Richard Black analyses key elements of the US-backed climate deal agreed in Copenhagen.
One widely-accepted definition of "dangerous climate change" is that it begins at a global temperature rise of 2C.
The Intergovernmental Panel on Climate Change (IPCC) recommends that to have a good chance of avoiding this definition of "dangerous climate change", developed countries cut emissions by at least 25% from 1990 levels by 2020, and that global emissions must peak and begin to decline by 2020 at the latest.
This agreement "recognises" the 2C goal but does not endorse it. There is no peak year, and no collective target for cutting emissions.
The EU considers this package so weak that it will maintain its lower pledge of keeping its emissions 20% below 1990 levels by 2020, rather than going to its alternative higher figure of 30%.
Other countries such as Japan and Australia are also likely to stick with their minimum levels of ambition.
This puts the globe more on track to a 3C rather than a 2C rise.
Sources close to the green business community say the deal is unlikely to stimulate investment in low-carbon technologies.
That requires either a functioning carbon market with a high enough carbon price to persuade companies to invest, or a state-directed system of financial levers.
Without near-term ramping-up of research, development and deployment of low-carbon technologies, the date by which emissions peak moves further into the distance, if it happens at all.
The essential partners in this deal were the US and China. India, Brazil and South Africa played supporting roles - creating the kind of deal that suits the emerging major economies.
The EU did a lot of the spadework on the day before leaders arrived. But reportedly, it was not informed that Mr Obama and Mr Wen had done a deal and were preparing to announce it.
The EU could have prevented this from becoming adopted as a global deal by refusing to endorse it.
As it does not meet the minimum standards for an acceptable package that several European countries had put forward, they had a politically defensible reason for turning it down. If they had, many if not all of the smaller developing countries would probably have followed them.
In the end, the EU decided not to stand up against the US and China, which emerge as the winners of this political game.
Ethiopia' President Meles Zenawi emerged as Africa's political victor - the chosen champion of France and the UK as they sought African support for their finance proposal. He delivered the African Union.
An immaculately choreographed presentation sequence by the White House saw US journalists only invited into crucial meetings and given briefings ahead of others.
Mr Obama announced the deal live on air to a US audience before most governments had even seen the document involved, ensuring he set the editorial agenda, at least in the US.
Exclusion of NGOs and press from the final day's politicking ensured scrutiny of draft agreements was always a beat behind the action.
Senators opposed to cap-and-trade legislation may call the president over less than firm language on monitoring and verification of developing countries' emissions.
INTERNATIONAL ENVIRONMENTAL GOVERNANCE
The concept that global environmental issues can and should be tackled on a co-operative international basis has taken a massive, massive blow.
The UN climate convention is the flagship agreement, and its outcomes are supposed to be negotiated. This deal was presented to the greater body of countries on a take-it-or-leave-it basis by small group of powerful players.
It is now debatable whether the UN climate convention has a meaningful future, or whether powerful countries will just decide by themselves, or in a small group, by how much they are prepared to cut emissions.
That makes optional the established schemes for helping the poorest countries towards a clean energy and climate-protected future.
The implications for other global treaties that are not meeting their goals, such as the UN biodiversity convention, can only be guessed at.