An iceberg is pictured in the western Antarctic peninsula on March 4. (Eitan Abramovich/AFP/Getty Images)

As over 150 nations assemble to sign the Paris climate agreement in New York on Friday, reams of new analysis are pouring out from the planet’s vital number-crunchers, who look at the fundamental relationship between how much carbon we put in the air and how much the planet’s temperature increases as a result.

And it’s adding up to a somber verdict: We seem closer to must-avoid climate thresholds than we thought — and crossing them may have bigger consequences than we recognize.

The Paris climate agreement pledges countries to keep the planet’s warming “well below” 2 degrees Celsius (3.6 degrees F) above pre-industrial levels, and to strive to keep warming as low as 1.5 degrees C (2.7 degrees F) above those levels. But here are four things you need to know about these targets, based upon four separate new and insightful analyses:

1.5 degrees C isn’t looking so far off lately. An analysis by Climate Central shows that the planet has been right around 1.5 degrees C all year this year, if you take temperatures from 1881-1910 to be the pre-industrial baseline. “The average global temperature change for the first three months of 2016 was 1.48°C, essentially equaling the 1.5°C warming threshold agreed to by COP 21 negotiators in Paris last December,” the group wrote. February of 2016, Climate Central calculates, was actually slightly warmer than 1.5 degrees C over pre-industrial levels.

The news isn’t as bad as it sounds: These have been some super-hot months, and El Nino is at least partly to blame. We’re likely to cool down some as El Nino ends — and we won’t truly have crossed the 1.5C threshold until the globally averaged temperature does over multiple years, so that it becomes the average. That will require far more than a few short months to happen.

Still, 1.5C hardly sounds theoretical lately. We already know what it feels like on a temporary basis, and it has coincided with mass coral bleaching, early Greenland melting and much more.

2 degrees C is considerably worse than 1.5. Meanwhile, a new study just out in Earth System Dynamics, by researchers with Climate Analytics, the Potsdam Institute for Climate Impact Research, and several other institutions has found that although 1.5C and 2C may not sound all that different, they actually are, in terms of their impacts.

“Before many have argued that there can’t be much difference because temperatures are so close and there’s so much uncertainty,” says Climate Analytics’ William Hare, one of the study’s authors. “But we’ve done an end-to-end uncertainty analysis, using 5 climate models and a state of the art impact assessment … to pull out some of the statistically significant signals.”

For instance, the study finds that “virtually all” tropical reefs the globe over are at risk of “severe degradation” at 2 degrees C starting in the year 2050, but that for a 1.5C scenario, that’s only 90 percent, and it actually lessens over the course of the century to 70 percent by its end. In other words, 1.5C just might save some coral reefs.

That’s not all the study found. In some regions of the globe, like the Mediterranean, water-availability risks are much worse at 2C than at 1.5C. In others, like parts of Africa, agricultural risks could be considerably higher, to list just a few of the findings. Extreme heat events also show a “substantial increase” in likelihood of occurrence at 2C, according to the study.

“There’s a really substantial reduction of risk for areas that are already hot and dry and suffering food and water shortages,” says Hare, if we hold warming to 1.5 rather than 2 degrees above pre-industrial levels.

Fast policy moves are needed to achieve either target. Meanwhile, an analysis by Climate Interactive and the MIT Sloan School of Management finds that the current Paris agreement pledges — made by individual countries as part of the agreement, and supposed to be improved upon over time — would still let the world warm by as much as 3.5 degrees Celsius by 2100. They obviously need to be ratcheted up, then.

How fast? The analysis finds that “with each year that countries wait to strengthen their current pledges, the rate at which emissions must decline gets steeper and steeper.” So if we wait for global emissions to peak in 2030, rather than in 2020, then every year after that they will have to decline by 4.6 percent per year, the analysis finds, a number that is “prohibitively fast.” If we peak in 2020, though, then reductions only have to happen at 3.2 percent per year, to stay under 2 degrees C, “a rate that has been achieved by some nations in the past.”

Thus, if possible, emissions should peak by 2020. The United States, in this scenario, would have to go from lowering its emissions 26 percent below 2005 levels by 2025 (its current goal), to cutting them by 45 percent by 2030. Other nations would have to make similarly large improvements on what they are currently promising to do. And even then, due to scientific uncertainty, the planet could still conceivably overshoot 2 degrees, and there is only a 66 percent or greater chance of getting there.

Of course, the actual embraced goal of the world is to stay “well below” 2 degrees, a target that suggests prudent avoidance, not walking right up to it and potentially going over.

Accordingly, the study also examined what it would take to suppress emissions fast enough to hit 1.5 degrees C. Here we’d have to have global emissions peak in 2020 and then decline by 5.9 percent annually thereafter. The United States, here, would have to get its emissions 60 percent below their 2005 levels by 2030. This is extreme, but then, that’s what it would take.

If we want to buy time, we have to save forests. There’s some good news here. According to an analysis by the Woods Hole Research Center, if we stop deforesting the tropics and instead move rapidly to restore these forests, we can buy 10 to 15 years longer to try to stay within 2 degrees C.

The reason is that if deforestation abruptly stopped — and stopped contributing to greenhouse gases each year — then forests would start growing back and sequestering carbon: pulling it back out of the air again. A current addition to our emissions would become a subtraction from them. Now that’s smart math.

“Proper forest management is the only climate change mitigation technology that is: 1) available immediately; 2) capable of providing negative emissions at the necessary scale; and 3) proven to have additional benefits for the local and global climate,” write the researchers.

Yes, that’s right — the world should simply stop chopping down trees immediately. Granted, while it may be theoretically possible to put the brakes on deforestation faster than it is to halt fossil fuel use, it seems unlikely that the underlying (economic) drivers of deforestation will suddenly end, either.

So what’s the upshot of it all?

This Earth Day, it’s hard to say the planet is in great shape. It is also hard to say that it is beyond saving, or at least, beyond beginning to repair. Rather, what happens next all depends on us.

Researchers say 2015 was the hottest year on record, and that it "smashed" the previous record, which was 2014. The Post's Chris Mooney explains what that could mean for weather patterns, the Paris climate deal and 2016. (Gillian Brockell,Chris Mooney/TWP)