Mr Miliband said more ambition was needed to stop global warming
The UK government has said it is "disappointed" the Copenhagen climate talks did not achieve legal commitments to reduce greenhouse gas emissions.
But Climate Change Secretary Ed Miliband said there had been "significant progress" towards a treaty and that attitudes were shifting.
However, nations had to "go much further", he told MPs.
Last December's talks failed to end in a legally binding agreement by the 193 member states of the United Nations.
However, key states, including the US and China, reached what they call a "meaningful agreement" on a number of issues, such as a recognition to limit global temperature rises to less than 2C.
Mr Miliband praised this, saying the support given for eventual payments of $100bn a year to help developing countries become greener would help.
He told MPs: "The outcome of Copenhagen was disappointing in a number of respects.
"We are disappointed that Copenhagen did not establish a clear timetable for a legal treaty and that we do not yet have the commitments to cuts in emissions that we were looking for."
But he said the accord between 49 developed and developing countries, endorsing the limit of two degrees warming as the benchmark for progress on climate change, could be built upon.
There had been "significant commitments" made by the richer nations to help developing countries combat global warming and tackle deforestation.
Mr Miliband said: "By any measure, these are important steps forward. But we know the world needs to go much further.
"We need more certainty and a greater scale of ambition. The urgent task ahead is to broaden, deepen and strengthen the commitments made at Copenhagen, drawing on the large coalition of countries that wanted more from the agreement."
Mr Miliband said: "The United States is seeking to get all countries to sign up to the accord and the UK is supporting this."
Speaking about the Copenhagen decision-making process, which would have required the support of all 193 countries to bring about a set of legally binding commitments, he said: "We need to find better ways of running the process of negotiation."
He added: "The global shift may not have yet found international legal form, but scientific evidence, public opinion and business opportunity have made it irreversible."
For the Conservatives, shadow energy and climate change secretary Greg Clark said Copenhagen had been a "flop".
He said the accord was "completely unclear about when emissions should be cut and by how much" and there was no clarity about the "sources of finance" for helping developing nations.
He added: "It's essentially an agreement to disagree, defined chiefly by what is absent from it, containing nothing to indicate the scale or timing of carbon reductions required of the world."
The Lib Dems said the summit should have been better organised and that disagreements between nations should not have been allowed to derail progress towards a legally-binding accord.
"Isn't the real truth that much of the efforts in Copenhagen were too little and too late?" said climate change spokesman Simon Hughes.