By Alissa de Carbonnel and Nina Chestney
BRUSSELS/LONDON (Reuters) - Britain's exit dashes the European Union's leadership ambitions on efforts to slow climate change, leaving the bloc on the sidelines while others endorse the global pact it championed to curb greenhouse gas emissions.
Last week, EU environment ministers jointly called for action "as soon as possible" to avoid being absent when the deal struck in Paris last December to limit global average temperatures below 2 degrees Celsius locks into place.
Britain's vote to leave the union has disrupted everyday affairs and probably displaced climate concerns as a political priority. It also removes one of the EU's strongest voices in favor of emissions-cutting policies.
The Paris Agreement will take effect once 55 nations responsible for 55 percent of man-made emissions ratify it.
With India, China and the United States hastening to lock in their pledges this year, some experts predict that could even be by the next round of climate talks in November in Marrakesh.
The EU's reversal from being the key broker clinching the landmark deal to lagging on its ratification and implementation would deal a blow to the bloc's credibility and influence on how the global climate rules are written.
"The likely scenario is that come Marrakesh, the EU will be very embarrassed," said an EU source close to the talks.
Britain has long championed the fight against global warming: it was one of the first nations to adopt a legally-binding framework to cut emissions with its Climate Change Act in 2008.
At U.N. climate talks in Paris, it committed to a single EU target of reducing emissions by at least 40 percent by 2030 from 1990 levels with the 27 other EU nations.
"It (Brexit) would reduce the level of clout of the EU in UN climate negotiations," said Ruth Davis, a political adviser to Greenpeace and a senior associate at E3G. "I'm afraid that overall I see that as a lose-lose."
WANING CLIMATE AMBITION?
This week, UN climate chief Christiana Figueres raised the prospect that the EU might need to reassess its emissions target.
The climate deal requires the bloc as well as each of the nations it spoke for in Paris to ratify simultaneously. So the EU is only ever as fast as its slowest member.
France and Hungary are the only EU countries to have ratified so far. Some want to wait for the EU breakdown of how the EU will share out the burden of meeting the 2030 target - a complex proposal that is due next month.
On Wednesday, Britain's secretary of state for energy and climate change Amber Rudd said it would not step back from international leadership on climate change.
The EU executive says it foresees no changes to the agenda, and some EU officials insist the lawmaking will press on, with Britain remaining a formal member of the EU for at least two years during the exit negotiations.
"They (Britain) are in until the end," one EU diplomat said. "We continue negotiating as 28 for now."
Privately, however, others see delays to the proposal on how to implement the Paris deal to avoid it being challenged later.
"What do you do with the U.K., effort which was a piece of the whole puzzle?" an EU official asked. "There's uncertainty: people don't know and Brits don't know either."
Meanwhile, some fear Britain's diminished voice will allow to member states such as Poland to dilute measures to curb their reliance on coal or improve air quality.
"This is at very best a massive distraction and at very worst disruption," said Rachel Kyte, chief executive of U.N. body Sustainable Energy for All. "Having a strong Europe push from the front has been a repeated pattern of breakthroughs."
(Additional reporting by Barbara Lewis in Brussels; Editing by Ruth Pitchford)