But average surface temperature alone doesn't paint a full picture. Temperature anomalies — how much the temperature of a given area deviates from what would be "normal" in that region — will swing wildly.
In the summer of 2012, 97% of the Greenland Ice Sheet's surface started to melt. That's typically a once-in-a-century occurrence, but we could see extreme surface melt like that every six years by end of the century.
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Without controlling our emissions (a business-as-usual scenario), the tropics would stay at unusually hot temperatures all summer long. In the temperate zones, 30% or more of the days would have temperatures that we currently consider unusual.
Even a little bit of warming will likely strain water resources. In a 2013 paper, scientists projected that the world will start to see more intense droughts more often. Left unchecked, climate change may cause severe drought across 40% of all land — double what it is today.
And then there's the weather. If the extreme El Niño event of 2015-2016 was any indication, we're in for more natural disasters — storm surges, wildfires, and heat waves are on the menu for 2070 and beyond.
Right now, humanity is standing on a precipice. If we ignore the warning signs, we could end up with what Schmidt envisions as a "vastly different planet" — roughly as different as our current climate is from the most recent ice age.
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Or we can innovate. Many best-case scenarios assume we'll reach negative emissions by 2100 — that is, absorb more than we emit through carbon-capture technology.
Schmidt says the Earth in 2100 will be somewhere between "a little bit warmer than today and a lot warmer than today." On a planet-wide scale, that difference could mean millions of lives saved, or not.
(Photo credit NASA / SPL / Barcroft Images / Barcroft Media via Getty Images)
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That said, it's still not exactly clear if Ross 128b is habitable.
"While the scientists involved in this discovery consider Ross 128b to be a temperate planet, uncertainty remains as to whether the planet lies inside, outside, or on the cusp of the habitable zone, where liquid water may exist on a planet’s surface," the European Southern Observatory (ESO) said in a statement announcing the discovery.
Ross 128's quiet nature makes it special.
Proxima Centauri, which is also a red dwarf 4 light-years from Earth that plays host to its own Earth-sized world, might be a bit too active to allow life to develop nearby over the course of billions of years. But it seems that Ross 128 may not have that problem.
Plus, astronomers of the future may have the chance to study Ross 128 and its possibly habitable planet from very close range.
Right now, the star is speeding toward Earth's part of space. According to the ESO, in about 79,000 years, the object will become the second-closest star from Earth (after the sun), moving closer than Proxima Centauri.
During the coming decades, scientists hope to use powerful tools to peer deeply into the atmospheres of planets outside our solar system in order to see exactly which worlds may or may not be habitable.
The ESO's Extremely Large Telescope, for example, will be able to look for chemicals in the atmosphere of other planets that could be indicators of life, according to the organization, and NASA's James Webb Space Telescope, slated for launch in 2019, will also have the ability to parse out the compositions of alien atmospheres.