MPs have called on the prime minister to set aside previous commitments and attend the upcoming Rio+20 summit on global sustainable development.
World leaders are due to gather for the meeting in Brazil's capital in June. The summit marks twenty years since 1992's Earth Summit, which set goals for tackling climate change and poverty.
Environment Secretary Caroline Spelman is due to attend in David Cameron's place, as the meeting clashes with the Queen's Diamond Jubilee celebrations.
But opening an estimates day debate on preparations for the summit, on 28 February 2012, Labour MP Joan Walley told the Commons it was essential for the prime minister to represent Britain.
"At a time when the world is changing, when environmental debt needs to be as high on the agenda as economic debt... when we have this one opportunity for the international community to frame new priorities, to work out how we each individually and collectively engage with this, we need the UK prime minister actively shaping the new agenda," the chair of the Environmental Audit Committee said.
Conservative MP Mark Spencer agreed, adding that the British government had a "moral responsibility to go to Rio and negotiate the best deal we can for the globe".
The DUP's Ian Paisley said the PM's attendance would give the "necessary panache, the necessary proof" that the environment was top of the government's agenda.
Liberal Democrat Martin Horwood agreed, telling MPs: "The political message of who attends the summit is very important."
He said Mr Cameron should attend "if he possibly can" because "that would send exactly the right message that, 20 years on, we are turning youthful idealism into real leadership and tangible action at governmental and global level".
Winding up for Labour, Fiona O'Donnell said the UK needed an "ambitious government that leads the world".
"To have credibility, it isn't enough to talk the talk, it has to walk the walk too," she told MPs.
Responding for the government, Environment Minister Richard Benyon said the government's priority for the upcoming summit was to "stand up and make a clear statement that sustainable development is the only way forward".