The UN Climate Summit (COP25) ended this Sunday in Madrid with a modest agreement, postponing until next year a key decision on global carbon markets.

Delegates from almost 200 nations endorsed a declaration to help poor countries suffering the effects of climate change but didn't allocate any new funds to do so.

The final agreement highlighted the ''urgent need'' to cut greenhouse gases in line with the goals of the landmark 2015 Paris climate change accord.

But despite holding the longest climate talks ever in 25 annual editions, many delegates resisted calls to enhance pledges to cut greenhouse gases next year.

The Paris accord established the common goal of avoiding a temperature increase of more than 1.5 degrees Celsius (2.7 degrees Fahrenheit) by the end of the century. So far, the world is on course for a 3- to 4-degree Celsius rise, with potentially dramatic consequences for many countries, including rising sea levels and fiercer storms.

The thorniest issues, including carbon markets, were left for the next summit in Glasgow in a year's time.

Environmental groups and activists accused the world's richer countries of showing little commitment to seriously tackling climate change.

'Disappointment'

UN Secretary-General Antonio Guterres said he was "disappointed" by the meeting's outcome.

The international community lost an important opportunity to show increased ambition on mitigation, adaptation and finance to tackle the climate crisis,'' he said.

``"We must not give up and I will not give up."

350, an environmental NGO, issued a statement slamming the results of the summit.

"As COP25 comes to an end, national delegates failed once more to step up to the existential challenge of the climate crisis," the non-profit said.

"These talks reflect how disconnected country leaders are from the urgency of the science and the demands of their citizens in the streets," said Helen Mountford, Vice President for Climate and Economics, at the World Resources Institute think-tank. "They need to wake up in 2020."

Two-day extension, sleepless nights

Officials from almost 200 countries had extended their stay in Madrid for a second extra day after failing to reach a deal.

Talks were scheduled to conclude on Friday but lurched into Sunday as major economies and smaller states struggled to resolve outstanding issues under the 2015 Paris Agreement.

Some of the most vulnerable nations said their voices were not being heard.

"Over the last 24 hours, 90% of the participants have not been involved in this process," said Kevin Conrad, Papua New Guinea's climate envoy, echoing concerns expressed by some other developing countries.

Earlier, Chile faced fierce criticism after it drafted a version of the summit text that campaigners complained was so weak it betrayed the spirit of the Paris deal.

Carbon markets disagreements

"It's sad that we couldn't reach a final agreement on carbon markets, admitted the climate summit's chair, Carolina Schmidt, Chile's environment minister.

But European Union countries and others have said they prefer not to finalise rules on international carbon markets rather than to approve ones that could undermine efforts to cut greenhouse gas emissions.

“We are all looking for a compromise,” Frans Timmermans, the European Commission’s top official in charge of climate issues, said earlier on Friday. “But there is no way, no way, we could accept a compromise that jeopardises environmental integrity. Just no way."

Economists say allowing companies and rich countries to invest in carbon-cutting measures such as forest protection in poor countries could become a vital tool for lowering emissions, provided the markets are transparent and there is no double counting.

Elusive financing

Countries agreed to designate funds for the most vulnerable countries to compensate them for the effects of extreme weather, one of the most pressing issues for small island states.

Yet the delegates didn't clarify how to mobilize a $100 billion per year in climate financing by 2020, as it had been agreed to in Paris.

In 2013, countries agreed on a tentative system to channel such aid, known as the Warsaw International Mechanism.

But some rich countries, particularly the United States, have resisted attempts to hold them formally accountable for the impact their greenhouse gas emissions have on the climate, prompting criticism from developing nations.

“The US government is the largest humanitarian donor in the world,” a State Department official said Friday. “The WIM should be a constructive space to catalyze action on the wide range of loss and damage issues.”

“A divisive conversation on blame and liability helps no one,” said the US official, who spoke on condition of anonymity due to the sensitivity of the ongoing negotiations.

President Donald Trump has formally triggered the United States’ withdrawal from the 2015 Paris climate accord, a process that will be completed 4 November 2020, a day after the next US presidential election.

However dozens of countries have already said they will submit more ambitious emissions targets next year, though analysts say the commitments made so far aren’t enough.

Scientists have calculated that global emissions have to drop 7.6 per cent annually, starting next year, if the Paris accord’s goal of keeping global warming at 1.5 degrees Celsius (2.7 degrees Fahrenheit) by the end of the century is to be achieved.