Reuters: Nearly 200 nations have agreed a legally binding deal to cut back on greenhouse gases used in refrigerators and air conditioners, a major step against climate change that prompted loud cheers when it was announced on Saturday.

The deal, which includes the world’s two biggest economies, the United States and China, divides countries into three groups with different deadlines to reduce the use of factory-made hydrofluorocarbon (HFC) gases, which can be 10,000 times more powerful than carbon dioxide as greenhouse gases.

“It’s a monumental step forward,” U.S. Secretary of State John Kerry said as he left the talks in the Rwandan capital of Kigali late on Friday.

Under the pact, developed nations, including much of Europe and the United States, commit to reducing their use of the gases incrementally, starting with a 10% cut by 2019 and reaching 85% by 2036.

Many wealthier nations have already begun to reduce their use of HFCs.

Two groups of developing countries will freeze their use of the gases by either 2024 or 2028, and then gradually reduce their use. India, Iran, Iraq, Pakistan and the Gulf countries will meet the later deadline.

They refused the earlier date because they have fast-expanding middle classes who want air conditioning in their hot climates, and because India feared damaging its growing industries.

“Last year in Paris, we promised to keep the world safe from the worst effects of climate change. Today, we are following through on that promise,” said U.N. environment chief Erik Solheim in a statement, referring to 2015’s Paris climate talks.

Gaining momentum

The deal binding 197 nations crowns a wave of measures to help fight climate change this month. Last week, the 2015 Paris Agreement to curb climate-warming emissions passed its required threshold to enter into force after India, Canada and the European Parliament ratified it.

But unlike the Paris agreement, the Kigali deal is legally binding, has very specific timetables and has an agreement by rich countries to help poor countries adapt their technology.

A quick reduction of HFCs could be a major contribution to slowing climate change, avoiding perhaps 0.5 degrees Celsius (0.9 Fahrenheit) of a projected rise in average temperatures by 2100, scientists say.

Environmental groups had called for an ambitious agreement on cutting HFCs to limit the damage from the roughly 1.6 billion new air conditioning units expected to come on stream by 2050, reflecting increased demand from an expanding middle class in Asia, Latin America and Africa.

Benson Ireri, a senior policy adviser at aid group Christian Aid, said that all African countries had volunteered for the earlier deadline because they worried about global warming pushing more of their citizens into poverty.

“It was a shame that India and a handful of other countries chose a slower time frame for phasing down HFCs but the bulk of nations, including China, have seen the benefits of going for a quicker reduction. It’s also been encouraging to see small island states and African countries a part of this higher ambition group,” he said in a statement.

A scientific panel advising the signatories to the deal said phasing out HFCs will cost between $4 billion and $6 billion, said Manoj Kumar Singh, India’s joint secretary at the Ministry of Environment, Forest and Climate Change.

“The implementation starts from 2024 onwards so there is enough time to plan and mobilize finance,” he told Reuters.

Donors had already put $80 million in a fund to start implementing the agreement, said Gina McCarthy, administrator of the U.S. Environmental Protection Agency.But Sergey Vasiliev, the head of the Russian delegation, said Russia’s estimates of the costs were higher and argued countries’ contributions to a multilateral fund to help poor countries adapt their technology should be voluntary.

The details of the funding will be finalised at a later meeting.

“We think it is more than $10 billion and some experts estimated up to $20 billion,” he told Reuters.

The HFC talks build on the 1987 Montreal Protocol, which succeeded in phasing out the use of chlorofluorocarbons (CFCs), widely used at that time in refrigeration and aerosols.

The protocol contains provisions for noncompliance, ranging from the provision of technical and financial assistance to trade sanctions in ozone depleting substances, which will be widened to include HFCs.

The original aim of the Montreal Protocol was to stop the depletion of the ozone layer, which shields the planet from ultraviolet rays linked to skin cancer and other conditions.

That effort cost $3.5 billion over 25 years, said Stephen Olivier Andersen, the director of research at Washington-based think tank Institute for Governance and Sustainable Development. Scientists say it prevented two million cases of skin cancer.

HFC greenhouse gases: a factfile

Hydrofluorocarbon (HFC) gases are set to be phased out under a historic international deal that experts say could do a huge amount to curb global warming.

What are they?

HFCs are part of a family called F-gases, which have fluorine as a common component. They are mainly used in refrigeration, air conditioners and aerosols. 

They are cousins of chlorofluorocarbons (CFCs) – a notorious substance that depletes the ozone layer, the thin gaseous shield that protects life on Earth from dangerous solar rays.

Why are they being banned?

HFCs were brought in to replace CFCs, which were banned in 1992 under the 1987 Montreal Protocol to protect the ozone layer.

HFCs have done their part in the process to heal the ozone, but have become a big problem on their own: they are massively efficient at trapping heat from the Sun. As a result, they are major contributors to global warming.

A molecule of HFC can be nearly 15,000 times more effective at warming than a molecule of carbon dioxide, depending on the type. Most of the HFCs entering the atmosphere come from routine leaks in refrigeration and air conditioning.

How could the ban fight climate change?

Eliminating HFCs could reduce global warming by 0.5 C by 2100, according to a 2015 study by the Institute for Governance and Sustainable Development.

UN members, in the historic Paris Agreement sealed last year, set a goal of curbing global warming to less than two degrees Celsius (3.6 degrees Fahrenheit) over pre-industrial levels. 

At present, Earth is on course for several degrees of warming by 2100, scientists say. This would doom many parts of the planet to worsening floods, droughts, desertification, rising seas and storms.

The Paris deal is voluntary and hedged with uncertainty as to whether countries will ratchet up their efforts to “decarbonise” their economies, moving away from polluting fossil fuels.

Scrapping HFCs would at the least buy some time to make the switch to cleaner sources and boost energy efficiency.

How many HFCs do we produce?

HFC emissions have been projected to grow from around one gigatonne (a billion tonnes) of carbon dioxide equivalent per year today, to between four and nine a year by 2050.

The increase is largely due to an expected huge rise in the use of air conditioners in developing countries in the coming decades.

The European Union introduced regulations to control HFCs from 2015 and encourage the use of safer alternatives such as ammonia, water or gases called hydrofluoroolefins. Switching entails financial costs, which for India and some other developing countries was a sticking point in the negotiations.

What’s in the deal?

The agreement takes the form of an amendment to the Montreal Protocol, already deemed one of the most successful environmental agreements ever.

Reached after seven years of negotiations among 197 parties, it sets down three pathways for eliminating HFCs.

Developed countries will start to phase down HFCs by 2019. Developing countries will follow with a freeze in consumption levels in 2024, with some other countries following suit in 2028.

By the late 2040s, all countries are expected to consume no more than 15-20 per cent of their baseline levels. The deal is legally binding, meaning those who break it could face punishment.

Countries also agreed to provide “adequate financing” for HFC reduction, the cost of which is estimated at billions of dollars globally, according to the UN Environmental Programme. 

The exact amount of additional funding will be agreed at a meeting in Montreal in 2017. There will also be grants for research on affordable alternatives to HFCs.

(SOURCES: Intergovernmental Panel on Climate Change Fifth Assessment Report; European Commission; UNEP.)