The Tories and Lib Dems have called on David Miliband to join a cross-party consensus on climate change.
Scientists - and politicians - are worried ice sheets are melting
Tony Blair has asked the new environment secretary to look at setting up an office on global warming.
And Mr Miliband's predecessor, foreign secretary Margaret Beckett has said she will appoint a special climate change representative.
But the Tories and Lib Dems say real progress will not be made until there is cross-party agreement.
In a joint letter from Conservative environment spokesman Peter Ainsworth and his Lib Dem counterpart Chris Huhne, the parties call on Mr Miliband to sign up to an "environment contract" with "clear rights and responsibilities" for government, business and individuals.
"We appreciate that offers of assistance from opposition parties are not always well intended," said the letter.
"However, we would like to help put in place a robust, long-term framework capable of engendering the confidence on the part of investors and the public alike.
"We are therefore writing to ask that you join the existing cross-party agreement on climate change."
The cross-party consensus, which has been agreed between the Tories, Lib Dems, the SNP, DUP and Plaid Cymru, would commit the UK to reduce emissions by 60% by 2050, whoever is in power.
It also includes commitments to year-on-year emission reductions and the establishment of an independent body to ensure that such reductions actually take place.
Meanwhile, in a letter to Mr Miliband, who was handed the environment job in last week's cabinet reshuffle, Tony Blair repeated his warning that climate change "is the greatest long-term threat facing the world today".
He also underlined the government's track record so far in this area of "action not just words".
The prime minister said he wanted Mr Miliband to develop ideas that help individuals make small changes to their own lives that might make a difference to global warming and the environment.
And he asked the new environment secretary to work with other departments to deliver an energy review with a programme to reduce emissions.
Meanwhile, Foreign Secretary Margaret Beckett announced she was appointing a special representative on climate change.
She said the issue was the biggest challenge facing the planet and the foreign office had a key role to play in addressing it.
"We're creating a new globalisation section directorate general in the FCO [Foreign and Commonwealth Office] but I also wanted someone who I know is steeped in these issues with a small support team," she told BBC Radio 4's The World at One.
The representative will work on several international initiatives, including those reached at the Gleneagles summit last summer.
The putative cross-party pact came under strain early this week, when the Conservatives reacted angrily to Lib Dem claims they will use a meeting between the two leaders to test the extent of Mr Cameron's green beliefs.
While a Tory environment spokesman accused his Lib Dem counterpart of "playing politics" with climate change.
The Lib Dems say they want to know where Mr Cameron stands on key issues such as nuclear energy and vehicle excise duty.
"For the consensus to work we need clear policy commitments from David Cameron's Tories, not just warm words," said Mr Huhne for the Liberal Democrats.