ROME -- Leaders of the world's biggest economies agreed Sunday to stop funding coal-fired power plants in poor countries and made a vague commitment to seek carbon neutrality "by or around mid-century" as they wrapped up a Rome summit before the much larger United Nations climate conference in Glasgow, Scotland.

While Italian Prime Minister Mario Draghi and French President Emmanuel Macron described the Group of 20 summit as a success, the outcome disappointed climate activists, the chief of the UN and Britain's leader. The U.K. is hosting the two-week Glasgow conference and had looked for more ambitious targets to come out of Rome.

British Prime Minister Boris Johnson called the G-20's commitments mere "drops in a rapidly warming ocean." UN Secretary-General Antonio Guterres agreed the outcome was not enough.

"While I welcome the #G20's recommitment to global solutions, I leave Rome with my hopes unfulfilled -- but at least they are not buried," Guterres tweeted. "Onwards to #COP26 in Glasgow."

The G20 countries represent more than three-quarters of the world's greenhouse gas emissions, and Britain had hoped for a "G20 bounce" going into the Glasgow COP26 meeting. Environmentalists and scientists have described the UN conference as the world's "last best hope" for nailing down commitments to limit the global rise in temperature to 1.5 degrees Celsius (2.7 degrees Fahrenheit) above the pre-industrial average.

The summit laid bare the divisions that still exist between Western countries that polluted the planet the most historically but are now seeing emissions decline and the emerging economies led by China whose emissions are rising as their economies grow.

Britain pushed for a commitment to achieve climate neutrality or net-zero emissions, meaning a balance between greenhouse gases added to and removed from the atmosphere, by 2050.

The United States and the European Union have set 2050 as their own deadline for reaching net-zero emissions, while China, Russia and Saudi Arabia are aiming for 2060. The leaders of those three countries didn't come to Rome for the summit.

In the end, the G20 leaders arrived at a compromise to achieve climate neutrality "by or around mid-century," not a set year.

Before leaving Rome, U.S. President Joe Biden called it "disappointing' that G20 members Russia and China 'basically didn't show up" with commitments to address the scourge of climate change ahead of the UN climate conference.

Russian leader Vladimir Putin and Chinese President Xi Jinping are not expected to attend the conference in Glasgow, although they are sending senior officials to the international COP26 talks.

"The disappointment relates to the fact that Russia...and China basically didn't show up in terms of any commitments to deal with climate change. And there's a reason why people should be disappointed," Biden said, adding: "I found it disappointing myself."

Biden comments came in response to a reporter's question about the modest pledges made during the G20 summit.

"We made commitments here from across the board in terms of what we're going to bring to (COP26)," the president said. "As that old trade saying goes, the proof of the pudding will be in the eating."

Earlier in the day, Russian Foreign Minister Sergey Lavrov pushed back at the West's target date.

"Why do you believe 2050 is some magic figure?" Lavrov asked at a news conference. "If it is an ambition of the European Union, it is the right of other countries also to have ambitions....No one has proven to us or anybody else that 2050 is something everyone must subscribe to."

Italy's Draghi said the declaration went further on climate than any G20 statement before it. He noted that it referred to keeping the 1.5-degree global warming target within reach, something that science shows will be hard to accomplish unless the world dramatically cuts emissions from fossil fuels.

"We changed the goalposts," Draghi told reporters.

Canadian Premier Justin Trudeau said that G20 leaders were able to get together was in itself a success given the coronavirus pandemic.

"The fact that we have well laid out the table and know where the sharp edges are, and know what work we we're going to have to do at COP is a very positive step," Trudeau said.

The future of coal, a key source of greenhouse gas emissions, also proved one of the most difficult issues on which to find consensus for the G20.

At the Rome summit, leaders agreed to "put an end to the provision of international public finance for new unabated coal power generation abroad by the end of 2021." That refers to financial support for building coal plants abroad.

Western countries have been moving away from such financing and major Asian economies are following suit: Chinese President Xi Jinping announced at the UN General Assembly last month that Beijing would stop funding such projects, and Japan and South Korea made similar commitments earlier in the year.

China has not set an end date for building coal plants at home, however. Coal is still China's main source of power generation, and both China and India have resisted proposals for a G20 declaration on phasing out domestic coal consumption.

The failure of the G20 to set a target for phasing out domestic coal use was a disappointment to Britain. But Johnson's spokesperson, Max Blain, said the G20 communique "was never meant to be the main lever in order to secure commitments on climate change," noting those would be hammered out at the Glasgow summit.

John Kirton, director of the G20 Research Group at the University of Toronto, said the leaders "took only baby steps" in the agreement and did almost nothing new.

He pointed to the agreement to "recall and reaffirm" their overdue commitment to provide $100 billion in assistance to poorer countries and to "stress the importance of meeting that goal fully as soon as possible" instead of stating that they were ready to stump up the full amount.

The agreement to end international coal financing "is the one thing that's specific and real. That one counts," Kirton said.

Youth climate activists Greta Thunberg and Vanessa Nakate issued an open letter to the media as the G20 was wrapping up, stressing three fundamental aspects of the climate crisis that often are downplayed: that time is running out, that any solution must provide justice to the people most affected, and that the biggest polluters often hide behind incomplete statistics about their true emissions.

"The climate crisis is only going to become more urgent. We can still avoid the worst consequences, we can still turn this around. But not if we continue like today," they wrote, just weeks after Thunberg shamed global leaders for their "blah blah blah" rhetoric during a youth climate summit in Milan.

Greenpeace Executive Director Jennifer Morgan said the G-20 failed to provide the leadership the world needed. "I think it was a betrayal to young people around the world," she told The Associated Press on Sunday.

Aside from climate issues, the leaders signed off on a landmark agreement for countries to enact a global minimum corporate tax of 15%. The global minimum is aimed at deterring multinational companies from dodging taxes by shifting profits to countries with ultra-low rates where they may do little actual business.

The leaders also said they would continue work on a French initiative for wealthier countries to re-channel $100 billion in financial support to needier countries in Africa in the form of special drawing rights - a foreign exchange tool used to help finance imports allocated by the International Monetary Fund and also received by advanced countries.

The leaders said they were "working on actionable options" to do that and set the $100 billion figure as a "total global ambition" short of an absolute commitment. Some $45 billion has already been reallocated by individual countries on a voluntary basis.

The commitment reflects concern that the post-pandemic recovery is diverging, with wealthy countries rebounding faster due to extensive vaccinations and stimulus spending.

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Associated Press writers Jill Lawless and Sylvie Corbet contributed to this report. Aamer Madhani contributed from Washington.