Chris Huhne's resignation doesn't change the arithmetic of the Cabinet in terms of Lib Dem bums on seats. Yet green campaigners are already concerned that his absence from top-level discussions could have consequences for the government's policies on climate change.
Ed Davey is considered a safe pair of hands but is relatively inexperienced compared to Huhne, who according to Whitehall sources regularly challenged George Osborne, who many believe is a climate change sceptic.
A Downing Street spokesman said on Friday afternoon: "Edward Davey has been appointed. He will no doubt want to come into the job and read himself into the brief but I wouldn't expect a significant change of direction."
But Davey will inherit a struggle experienced by Huhne against Tories who believe climate change should be lower down the list of coalition priorities.
Environmental groups lamented the loss of Huhne, with Greenpeace head John Sauven saying: "He has been a vocal advocate for the green agenda in a government whose green credentials are looking more than a little tarnished."
His sentiments were echoed by Friends of the Earth's executive director Andy Atkins, who called on Ed Davey to "stand firm against George Osborne's anti-green agenda."
Huhne was seen as a champion of tackling climate change in the face of what some describe as the Treasury's "anti-green" agenda, credited with playing a significant part in getting global climate negotiations back on track in Cancun in 2010, after near-collapse at the summit in Copenhagen the previous year, and driving them further forward in Durban last year.
Caroline Flint, the shadow energy and climate change secretary, said the appointment of Davey would be a "much-needed opportunity for the government to change course".
"David Cameron promised this would be the 'greenest government ever'. But on his watch the Green Investment Bank has been delayed, thousands of jobs and businesses in the solar industry have been put at risk and the UK has fallen from third in the world for investment in green growth to 13th."
Conservative climate change sceptics were buoyed by George Osborne's speech to the Tory party conference in October, when he said the UK should cut its emissions "no slower but no faster" than other European nations.
The coalition is expected to come under increasing pressure to abandon the roll-out of smart meters, which have the potential to save energy but which are opposed by landlords who will have to pay to install them.
There is also pressure to curb the massive expansion of wind energy. Wind farms often annoy Tory voters living in the countryside on aesthetic and practical grounds. Chris Huhne was extremely keen to see the roll-out of wind energy, the challenge for Ed Davey will be to ensure this Lib Dem aspiration remains on the agenda.
George Osborne is said to be sympathetic to lobbying from a previous Tory chancellor, Lord Lawson, who is an ardent climate change sceptic. Chris Huhne has publicly attacked Lord Lawson over his beliefs on climate change in the past. The question will be whether Ed Davey - seen as an all-round nice guy - will be able to take on the Tories on these issues once he arrives at the Department for Energy and Climate Change next week.
In more general terms, Chris Huhne's resignation further damages the sickly Liberal Democrat brand, and his leaving government won't draw a line under it. The trial - which will have its first hearing on 16 February, could last some time. Doubtless every twist and turn will be followed by the media in the weeks to come. And until someone else in the Cabinet resigns (Cheryl Gillan resumes her place as bookies' favourite over her resistance to High Speed Rail), it's a Lib Dem (once again) whose fall from political grace will stick in the memory of would-be voters.
So although on the face of it the resignation doesn't change a huge amount, it means that two of the three cabinet resignations since the election have been Lib Dem, two of the party's most powerful figures are not in government, and there's nothing to suggest their poll ratings are improving.