KATOWICE, Poland (AP) — Three years after sealing a landmark global climate deal in Paris, world leaders are gathering again to agree on the fine print.

The euphoria of 2015 has given way to sober realization that getting an agreement among almost 200 countries, each with their own political and economic demands, will be challenging — as evidenced by President Donald Trump's decision to pull the United States out of the Paris accord, citing his "America First" mantra.

"Looking from the outside perspective, it's an impossible task," Poland's deputy environment minister, Michal Kurtyka, said of the talks he will preside over in Katowice from Dec. 2-14.

Top of the agenda will be finalizing the so-called Paris rulebook, which determines how countries have to count their greenhouse gas emissions, transparently report them to the rest of the world and reveal what they are doing to reduce them.

Seasoned negotiators are calling the meeting, which is expected to draw 25,000 participants, "Paris 2.0" because of the high stakes at play in Katowice.

Forest fires from California to Greece, droughts in Germany and Australia, tropical cyclones Mangkhut in the Pacific and Michael in the Atlantic — scientists say this year's extreme weather offers a glimpse of disasters to come if global warming continues unabated.

A recent report by the Intergovernmental Panel on Climate Change warned that time is running out if the world wants to achieve the most ambitious target in the Paris agreement — keeping global warming at 1.5 degrees Celsius (2.7 degrees Fahrenheit). The planet has already warmed by about 1 degree C since pre-industrial times and it's on course for another 2-3 degrees of warming by the end of the century unless drastic action is taken.

The conference will have "quite significant consequences for humanity and for the way in which we take care of our planet," Kurtyka told the Associated Press ahead of the talks.

Experts agree that the Paris goals can only be met by cutting emissions of carbon dioxide and other greenhouse gases to net zero by 2050.

But the Paris agreement let countries set their own emissions targets. Some are on track, others aren't. Overall, the world is heading the wrong way.

Last week, the World Meteorological Organization said globally averaged concentrations of carbon dioxide reached a new record in 2017, while the level of other heat-trapping gases such methane and nitrous oxide also rose.

This year is expected to see another 2 percent increase in human-made emissions, as construction of coal-fired power plants in Asia and Africa continue while carbon-absorbing forests are felled faster than they can regrow.

"Everyone recognized that the national plans, when you add everything up, will take us way beyond 3, potentially 4 degrees Celsius warming," said Johan Rockstrom, the incoming director of the Potsdam Institute for Climate Impact Research.

"We know that we're moving in the wrong direction," Rockstrom told the AP. "We need to bend the global carbon emissions no later than 2020 — in two years' time — to stand a chance to stay under 2 degrees Celsius."

Convincing countries to set new, tougher targets for emissions reduction by 2020 is a key challenge in Katowice.

Doing so will entail a transformation of all sectors of their economies, including a complete end to burning fossil fuel.

Poor nations want rich countries to pledge the biggest cuts, on the grounds that they're responsible for most of the carbon emissions in the atmosphere. Rich countries say they're willing to lead the way, but only if poor nations play their part as well.

"Obviously not all countries are at the same stage of development," said Lidia Wojtal, an associate with Berlin-based consultancy Climatekos and a former Polish climate negotiator. "So we need to also take that into account and differentiate between the responsibilities. And that's a huge task."

Among those likely to be pressing hardest for ambitious measures will be small island nations , which are already facing serious challenges from climate change.

The U.S., meanwhile, is far from being the driving force it was during the Paris talks under President Barack Obama. Brazil and Australia, previously staunch backers of the accord, appear to be following in Trump's footsteps .

Some observers fear nationalist thinking on climate could scupper all hope of meaningful progress in Katowice. Others are more optimistic.

"We will soon see a large enough minority of significant economies moving decisively in the right direction," said Rockstrom. "That can have spillover effects which can be positive."

Poland could end up playing a crucial role in bringing opposing sides together. The country has already presided over three previous rounds of climate talks, and its heavy reliance on carbon-intensive coal for energy is forcing Warsaw to mull some tough measures in the years ahead.

The 24th Conference of the Parties, or COP24 as it's known, is being held on the site of a Katowice mine that was closed in 1999 after 176 years of coal production. Five out of the city's seven collieries have been closed since the 1990s, as Poland phased out communist-era subsidies and moved to a market economy.

Yet elsewhere in the city, 1,500 miners still extract thousands of tons of coal daily. Poland also still depends on coal for some 80 percent of its energy needs.

Poland intends to send a signal that the miners' futures, and those of millions of others whose jobs are at risk from decarbonization, are not being forgotten. During the first week of talks, leaders are expected to sign a Polish-backed declaration calling for a 'just transition' that will "create quality jobs in regions affected by transition to a low-carbon economy."

Then negotiators will get down to the gritty task of trimming a 300-page draft into a workable and meaningful agreement that governments can sign off on at the end of the second week.

"(I) hope that parties will be able to reach a compromise and that we will be able to say that Katowice contributed positively to this global effort," Kurtyka said.

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Jordans reported from Berlin.

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Follow Frank Jordans on Twitter at http://www.twitter.com/wirereporter

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Read more stories on climate issues by The Associated Press at https://www.apnews.com/Climate