More countries than ever before have hit the expected peak of their planet-warming emissions - laying the groundwork to reduce them - but much more needs to be done, and fast, to curb emissions, researchers said on Thursday.

More than 55 countries - which together produce 60 percent of global emissions - have already peaked or are committed to peaking their emissions by 2030, a crucial step to curbing global warming, experts at the World Resources Institute (WRI) said.

Although this is encouraging, global emissions must peak by 2020 to keep global warming within safe levels, they said.

The longer it takes to peak emissions - the point when global emissions reach a maximum level and then decline - the more difficult and costly it will be to avoid dangerous levels of warming.

"This trend is encouraging, as reaching the peaking turning point is a necessary step before curbing emissions," the Washington-based research group said in a report.

"Nevertheless, the number of countries peaking and the emissions level at which they are peaking is insufficient to limiting warming to well below 2 degrees (above pre-industrial levels)."

"Countries must increase their ambition and go farther, faster," the report noted.

By 2010, 39 of the world's 43 developed countries had peaked their emissions, including the United States, Canada, Australia, Russia, and most of Europe. Brazil had also peaked.

Japan, South Korea and New Zealand are expected to peak by 2020. China, Mexico and Singapore are aiming for 2030.

To peak their emissions by 2030 or sooner, countries will need to stick to commitments they have made to help meet the Paris climate agreement goal of keeping global warming to well below 2 degrees Celsius.

Global emissions are projected to continue to rise between now and 2030 even if countries achieve their commitments under the Paris Agreement, WRI said.

And delaying the global peak date beyond 2020 will push temperatures above the Paris limit, making it more costly to reduce emissions and avoid the even more costly impacts of climate change, such as extreme droughts, floods and storms, it said.

Delaying action also will force countries to later try to remove large quantities of carbon from the atmosphere using unproven technologies - and creates the risk the planet will warm to dangerous levels, the researchers said.

An annual United Nations audit published on Tuesday showed emissions are likely to be far above the threshold for holding global temperature rise under 2 degrees Celsius.

But there are signs of a three-year plateau in carbon dioxide emissions from fossil fuels, cement production and other industrial processes, largely due to slower growth in coal use in China and the United States.

"We are at a watershed moment where we have stopped the rise in CO2 emissions. There is every reason to believe we can bring them down, and we see great news coming from all over the world, every day," U.N. Environment Programme chief Erik Solheim said on Tuesday.

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