On the eve of the most important global climate meeting in years, a definitive United Nations report has found that the world is well off course on its promises to cut greenhouse gas emissions - and may have even further to go than previously thought.

Seven major countries, including the United States, are well behind achieving the pledges they made in Paris three years ago, the report finds, with little time left to adopt much more ambitious policy measures to curb their emissions.

"We have new evidence that countries are not doing enough," said Philip Drost, head of the steering committee for the UN Environment Program's (UNEP) annual "emissions gap" report, released in Paris on Tuesday.

That verdict is likely to weigh heavily during a UN climate meeting that begins in Poland next week, where countries are scheduled to discuss how well they are, or are not, living up to the goals set in the landmark 2015 the Paris climate agreement.

The UNEP report finds that, with global emissions still increasing as of 2017, it is unlikely they will reach a peak by 2020.

Yet such a peak, required before any decline can occur, is a near mandatory outcome if the world is to have a chance of achieving the Paris agreement's most important goal: limiting the planet's warming to "well below" 2 degrees Celsius (3.6 degrees Fahrenheit) above preindustrial levels.

"All of the science suggests that peaking by 2020 is critical," said Kelly Levin, an analyst with the World Resources Institute and one of the report's lead authors. "If you miss that, we rely on much steeper reductions in the future."

Moreover, the report finds the gap between countries' Paris promises and emissions levels that would be needed to stay consistent with the Paris agreement is even larger than previously believed.

Because of all of this, the report says, the stakes are now higher. "Concerns about the current level of both ambition and action," it says, are now amplified in comparison with previous years.

Here is why. Current global emissions were 53.5 billion tons of carbon dioxide equivalents in 2017; if all countries live up to all promises made in Paris, they would also be about 53 billion tons in 2030. (Emissions are projected to grow with the growth of populations and economies, so basically, under the current Paris promises, the world is running simply to stand still.)

This sets the world on a path to about 3 degrees Celsius (5.4 degrees Fahrenheit) of total warming by 2100.

Hence the gap. Emissions can be about 40 billion tons annually in the year 2030 to preserve good odds of holding warming to 2 degrees, the UNEP report finds.

And for 1.5 degrees Celsius, they would have to fall to 24 billion tons or so by that year - an extraordinarily steep plunge.

In a middling scenario that is also consistent with the Paris agreement's language but takes more risk with the planet - holding warming below 1.8 degrees C - emissions would have to fall to about 34 billion tons by 2030.

Earth has already warmed about 1 degree Celsius - 1.8 degrees Fahrenheit - above preindustrial temperatures, as recorded in the latter part of the 19th century.

And because that figure is a global average, some areas - especially the Arctic - are already considerably warmer than that.

Current actions by major emitting countries - all of whom agreed in 2015 to be part of the Paris climate agreement, though the United States is now backtracking - are not nearly enough to prevent another half-degree or more of warming, the report finds.

"We need three times more ambition to close the 2-degree gap, and five times more ambition to close the 1.5-degree gap," Drost said.

In calling for dramatically more action in a very short period of time, the new document matches the dire verdict reached last month by scientists who are part of the UN's Intergovernmental Panel on Climate Change.

Their report concluded global emissions must be sharply cut and that this must happen in 12 years, by 2030 to preserve a chance of limiting temperatures to a rise of 1.5 degrees Celsius.

But the new UNEP document presents considerably more direct policy analysis and perhaps even some finger-pointing.

The document goes through G-20 member nations one by one, listing which ones are failing to live up to the promises they made in Paris three years ago (promises that, themselves, are far too little to keep the planet's warming in check).

Together, the G-20 countries account for 78 percent of the globe's emissions.

Seven of these countries - Argentina, Australia, Canada, the Republic of Korea, Saudi Arabia, South Africa and the United States - are off track to meet their Paris promises for the year 2030, the UNEP report finds. So is the entire European Union.

Several other G-20 countries - Russia, India and Turkey - are already on course to exceed their Paris promises by a good measure, but the report questions whether this may in part be because they have set their ambitions too low.

For two more G-20 countries - Mexico and Indonesia - it just is not clear where they are with respect to their goals. And even for those few countries that are on target - Brazil, China Japan - there is plenty to worry about.

For example, Brazil has just elected a populist leader, Jair Bolsonaro, who some fear will enact policies that could lead to further deforestation of the vast Amazon rain forest and, therefore, far larger greenhouse gas emissions from Brazil.

In light of all this, it is little surprise that global emissions ticked upward again last year after three years - 2014 through 2016 - during which they appeared to flatten out.

That brief hiatus for rising emissions now appears to have been a blip. Overall, the world continues to move in the wrong direction, and, as the G-20 analysis shows, the blame can kind of be spread around.

"Rich countries need faster reductions; the poorer countries need to slow down the growth," said Glen Peters, research director of the Center for International Climate and Environmental Research in Oslo and a report author. "No one is doing enough."

The problem is not only what countries are or are not doing - it is our evolving understanding of what is necessary and what is even possible to do.

The new UNEP report finds a larger gap between the world's promises and tolerable emissions levels in 2030, especially if we want to brake Earth's warming to the most stringent limit of 1.5 degrees Celsius.

Just last year, the report found the emissions gap for 2 degrees Celsius of warming was 11 billion to 13.5 billion tons of carbon dioxide equivalents in the year 2030, while the gap for 1.5 degrees Celsius was 16 billion to 19 billion tons.

But this year, the report revises those figures. The gap for 2 degrees is now 13 billion to 15 billion tons in 2030, and for 1.5 degrees it is 29 billion to 32 billion tons.

The latter figure in particular may seem a shocking change, but it is important to understand how it came about.

Scientists have become increasingly critical of future temperature and emissions scenarios that contain a large volume of "negative emissions" - a reliance on massive-scale technologies to remove carbon from the air.

When programmed into computer models, such technologies gave the impression that the world could temporarily exceed a given temperature target, such as 1.5 degrees Celsius, by a good measure but then cool Earth down again through carbon removal.

But criticism has been mounting, as the required technologies do not yet exist at scale and would require massive amounts of land and energy inputs, or cause other perturbations that would make them unpopular and difficult to scale up.

"A lot of the latest scientific literature tried to be more cautious about the reliance on really large-scale carbon removal," Levin said.

That is one reason the emissions gap now appears larger: The fewer negative emissions there are later in the century, the larger emissions cuts would have to be in the present and near future.

Another reason for the growing gap is more artificial; it turns on how the analysis is organized.

The new report now analyzes possible climate and emissions pathways in three buckets - those that limit warming to 2 degrees, 1.8 degrees and 1.5 degrees - rather than two (for 2 degrees and 1.5 degrees), as in previous years.

The result is that only the most stringent scenarios are now included in the 1.5-degrees grouping, said Peters, while scenarios that are still compliant with the technical language of the Paris agreement - exceeding 1.5 degrees, but not 2 degrees - allow for somewhat more emissions. So ultimately, it is really about how much risk we want to take with the planet.

"There's a lot of air between the 1.5 range and the 2-degree range," Peters said.

No matter what, the new report seems sure to cause even more soul-searching at the two-week UN climate summit in Poland. "They have really increased this message around urgency," Levin said. "We can add this to the pile of reports that are clear calls for action, and the call is getting louder with every minute we delay."

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