Cutting back harmful hydrofluorocarbons (HFCs), used in refrigeration, aerosols and air conditioning, could avoid global temperature rise of 0.5 degrees by end of century

By Francois Murphy and Lesley Wroughton

VIENNA, July 22 (Reuters) - U.S. Secretary of State John Kerry urged U.N. nations on Friday to reach a deal to cut the use of a family of powerful greenhouse gases and take a big step towards keeping global warming in check.

Officials from nearly 200 countries are meeting this week to hammer out an agreement to cut the use of hydrofluorocarbons (HFCs), which are used in refrigeration, aerosols and air conditioning, by amending the landmark Montreal Protocol.

The Montreal Protocol succeeded in slashing the use of chlorofluorocarbons (CFCs), which damage the ozone layer. The HFCs that have often replaced them, while better for the ozone layer, are greenhouse gases far more potent than carbon dioxide.

A deal to replace HFCs could avoid a global temperature increase of 0.5 degrees Celsius by the end of the century, officials say - a big step towards implementing the goal set in last year's Paris climate pact of a rise of less than 2 degrees.

"I think that we probably all recognise that an awful lot of the world, most of the world, doesn't know this meeting is taking place," Kerry, the only foreign minister attending the meeting of environmental officials, said in a speech to delegates.

"But the truth is our goal for these talks, amending the Montreal Protocol to phase down HFCs, is one of the single most important unitary steps that we could possibly take at this moment to stave off the worst impacts of climate change," he added.

The Vienna meeting's objectives include agreeing on schedules for countries to reduce HFC use and on financial help for developing nations to cut their use. A final agreement is due to be reached at meeting in Rwanda's capital, Kigali, in October.

"The goal of the meeting is to get as far as possible, but while it would be a wonderful outcome, I don't expect to complete the negotiations here in Vienna," a senior U.S. official said on condition of anonymity.

"We expect and hope that the parties will narrow the issues and reach agreement on some elements so that we are on track to finalize the amendment when parties reconvene in Kigali in October," the official added.

Kerry said progress had been made towards overcoming resistance from hot and developing countries related to the difficulties and cost of switching to more environmentally friendly products.

"In the last two days I have talked personally with his royal highness the deputy crown prince of Saudi Arabia, who agreed that we need to try to move forward and we had a good conversation about it, and we know we can do it with countries that have a high ambient (temperature) challenge," he said.

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