We're probably not going to hit the world's most important climate goal

2 degrees Celsius.

It's one of the most widely-publicized numbers in the world. In 2015, world leaders convened in Paris and agreed to limit the planet's warming this century to below 2 degrees Celsius above pre-Industrial Revolution temperatures — and possibly even cap Earth's warming at an ambitious 1.5 degrees Celsius (or 2.7 degrees Fahrenheit).

To get there, leaders proposed rapidly slashing heat-trapping carbon emissions from power plants, cars, and industry. But it wasn't ever going to be easy. And in a new study published in the American Geophysical Union journal Earth's Future, researchers argue that meeting 2 C climate targets is currently far, far out-of-reach, to put it gently. Even if the four biggest carbon-emitters — the U.S., China, the EU, and India — succeeded in dramatically ramping down their emissions over the next few decades, the rest of the world would need to radically cut their carbon emissions to nearly zero by 2030 — and stay there. That's nearly impossible.

"Even if you could achieve emission reductions — which is itself a Herculean task — very little is left over for the rest of the world," said Christopher Green, an environmental economist at McGill University and study coauthor.

"There would be almost nothing left over for the rest of the countries to emit."

Beyond some big industrial players like Japan and Russia, many still-developing countries in vast swaths of Asia, South America, Africa, and beyond will almost certainly emit ample amounts of carbon in the coming decades. They have a right to, and a desire for the simple, taken-for-granted, life-improving technologies of the Western world, like refrigeration and electricity.

"The world’s middle class has been growing at an unprecedented rate, and as you move up the income ladder, your carbon footprint expands," Bill Gates, who is funding futuristic carbon-free technologies, blogged in 2018. "Your family eats more eggs, meat, and dairy, so they get better nutrition. You’re in the market for a refrigerator, electric lights so your kids can study at night, and a sturdy home built with metal and concrete."

What this means is — in order to meet the Paris climate goals — there's an even bigger squeeze on the big players like the U.S, the EU, and China to slash carbon emissions from all sectors of society. "There will have to be a radical increase in the ambitions," said Glen Peters, the research director at the Center for International Climate Research and also a study coauthor.

SEE ALSO: Since the first Earth Day, the planet’s CO2 levels have gone off the rails

Over the past few years, there has been much discussion and published research on how to meet the Paris climate targets. One roadmap suggests halving the globe's human-made carbon emissions each decade for the next 30 years. Cutting carbon emissions in half by 2030 is an ambition touted by Green New Deal advocate U.S. Representative Alexandria Ocasio-Cortez. It's laudable, but as Green emphasized, it will take a "Herculean effort." And critically, it's just not feasible for well over 100 countries to so rapidly bring their collective carbon emissions down to zero.

"It all sounds nice and catchy," said Peters. "It sounds plausible when it's nice and catchy. But when you convert it into what it means for individual countries, it's extreme."

It's extreme because it means transforming societies, whether big, medium, or smaller carbon emitters. In China, it means shutting down a fleet of coal plants over the next decade — but the flourishing economic power is building more. In the U.S., it means radically scaling up renewables to replace fossil fuel power plants — in a political climate where the current presidential administration publicly fosters climate science misinformation. What's more, the U.S. used "more energy than ever before" in 2018, according to the U.S. Energy Information Administration.

As of now, global carbon emissions aren't expected to even peak until 2030. "That's deeply problematic," said Kelly Levin, a senior associate at the World Resources Institute, an environmental research organization. Levin had no role in the study.

This all sounds pretty darn pessimistic. But Peters and Green are making an objective point. If global nations really want to limit warming at 2 C, they're going to have to radically ramp up carbon free renewables and other advanced technologies. They'll have a chance to start doing this in 2020, when global nations convene at a still-undetermined location to make new, deeper climate pledges. "One question is how the major emitters are going to come to the table by 2020," said Levin. "Clearly, we need a very different emissions trajectory in the next few years if we're to limit to 1.5 or 2 degrees."

1.5 C is a far more ideal option, according to United Nations scientists. Stabilizing the climate at 1.5 C means avoiding the worst consequences of extreme weather and debilitating drought.

But 1.5 isn't realistic today. "It's magical thinking at this point," said McGill's Green. That's because society doesn't currently have the means of capping warming at 1.5 C, or 2 C. "We need a focus on the means," said Green. He's talking about "break-through technologies," the type touted by Bill Gates at the Paris climate accords.

"The hero of Paris was Bill Gates," emphasized Green, noting that Gates lobbied wealthy nations to develop these new energy technologies at the convention. These low carbon, sometimes futuristic technologies include nuclear fusion power plants (something that's in development but perhaps decades away), cheaper traditional nuclear power, and capturing carbon and storing it in the ground.

This also means ramping up proven carbon-free technologies, like solar and wind farms, which are flourishing in vast swaths of the U.S., but still aren't nearly as widespread fossil fuels. It also means building massive batteries to store energy from these renewable power farms. Los Angeles, for example, recently announced plans to phase out three big natural gas-powered plants and construct battery storage by 2029.

Image: Jiang et al / AGU

Meeting the Paris temperature limits could be so beyond reach, the study's authors suggest it might be necessary to deploy risky solar geoengineering to cool the planet. That would entail pumping reflective particles or droplets into the atmosphere to reflect sunlight, possibly by using blimps. "It is hard to argue against their conclusion that we need to start seriously considering options such as the deployment of solar geoengineering, with all of the risks that entails, if the world is serious about achieving the Paris Agreement goals,” Dáithí Stone, a climate scientist at New Zealand's National Institute of Water and Atmospheric Research, said in a statement.

As is overwhelmingly apparent, it will be challenging — and historically unprecedented — to slash carbon emissions in the coming decades to meet the 2 C climate goals. But, that's not surprising. The atmospheric changes humanity has wrought on the planet are of geologic magnitudes.

"What’s important to recognize is the changes humanity is driving at present are commensurate with the most significant events in the history of life on this planet," National Center for Atmospheric Research scientist Matthew Long told Mashable. Carbon dioxide concentrations are already the highest they've been in millions of years. Since the first Earth Day in 1970, the rate of carbon dioxide increase in the atmosphere is unprecedented. Limiting the planet's warming to Paris climate targets, then, is seriously ambitious.

And it will take ambitious means.

"This is a very difficult problem to solve," said Green, noting that grandiose pledges to cut emissions and half-measures won't do the trick. "You'll never fool the atmosphere."

WATCH: Ever wonder how the universe might end?