The world needs to get to net-zero carbon emissions by the 2030s to have a chance of avoiding the worst effects of climate change.
That's the stark message delivered in a sweeping report on the current scientific consensus on climate, released Monday by the UN’s Intergovernmental Panel on Climate Change (IPCC).
The report's scope is global, but here are five takeaways for folks who live in and around Boston:
Here's a term you'll be hearing more often: 'weather whiplash'
Climate change is causing increased variability in the global water cycle, so regions will see more severe swings between wet and dry. We're starting to see some of this in New England, like this year's early-summer heat and abnormally dry weather followed by the wettest July on record. More of that is on the way. And while we're talking about heat ...
You thought June was hot? More heat waves are coming
Heat waves — like the ones that hit Boston in June — are now occurring five times more often across the globe than before 1850. If global warming hits 2 degrees Celsius, heat waves will be 14 times more common, and cities will feel it the most.
"Cities intensify warming on a local scale," said Ko Barrett, vice chair of the IPCC and Deputy Assistant Administrator for Research at the National Oceanic and Atmospheric Administration (NOAA). "Cities will experience increases in the severity of heat waves since urban areas are usually warmer than their surroundings."
Cities create and retain heat because they have lots of buildings (and lots of people) close together, and a surplus of dark surfaces that absorb heat. Boston was recently ranked sixth in the country for heat intensity, and this past June was the hottest ever recorded here.
Sea level will rise by 2050, no matter what we do
Another sobering message for Boston: Projected sea-level rise for the next few decades is largely irreversible.
"Sea-level change through the middle of this century, around 2050, has largely been locked in regardless of how quickly we get our emissions down," said Bob Kopp, a climate policy scholar at Rutgers University's department of Earth & planetary sciences, and one of the report authors. "We're likely looking at about 15 to 30 centimeters — or about six to 12 inches — of global average sea-level rise through the middle of the century."
The water could get way higher if we don't cut emissions. Like, six feet higher
The sea-level rise we have set in motion will continue well past the end of this century. What the world does over the next decade will make the difference between bad and really, really, really bad.
"When we go out to 2100, then we start to see a difference with what we do," said Baylor Fox-Kemper, a professor of Earth, environmental and planetary sciences at Brown University, and one off the authors of the report. "For very low emissions, we see maybe one to two feet of sea-level rise. And for very high emissions, we see two to three feet of sea-level rise."
"And there are changes that we can't rule out that might happen in both Greenland and Antarctica to the ice sheets that could make that sea level rise as high as six feet under high-emission scenarios by 2100."
The different degrees of sea-level rise, he adds, will mean the difference between coastal flooding that's hundreds of times more likely than today, or many hundreds of times more likely.
One bit of good news, kinda: The Gulf Stream probably won't fail this century
The Gulf Stream, a flow of warm water in the Atlantic that runs from Florida up the East Coast of the United States, is part of a larger ocean system called the Atlantic Meridional Overturning Current. The whole system plays a large role in weather patterns and sea-level rise, and there's growing evidence that climate change is weakening the system more quickly than anticipated.
But happily, the entire system does not appear to be in danger of imminent collapse, as some have feared. That's great news because "were it to collapse, we would see a little bit over a foot of sea level rise here in New England right away," said Fox-Kemper. "That would be, you know, a low-likelihood but high-impact outcome."
Peter Frumhoff, chief climate scientist with the Union of Concerned Scientists and an author on a previous IPCC report, agreed that ocean currents like the Gulf Stream are critical systems to watch.
"We really don't know exactly what the triggers are for this and for other, what are loosely called 'tipping points,'" he said. The best way to keep from tipping the tipping points? "Stop digging the hole that we're that we're digging and transition to clean energy and and a low-carbon future."
We're in the middle of a climate change choose-your-own-adventure novel, and we still have time to make the right choices
This is all pretty grim. But think of it this way: It's kind of like the planet has scary high cholesterol. That's not healthy, but if we use a couple different methods to chip away at emissions steadily, we'll get to an OK place. Maybe even — eventually — a better place. But right now, we're gorging at the fossil fuel buffet, and if we keep it up, we'll be pretty much out of options.
"The projections forward include a very broad range of scenarios which are scenarios about human choice," said Frumhoff. "Do we remove the political obstacles to reducing fossil fuel and other greenhouse gas emissions? Or do we continue the 'business as usual' way?
"The way the differences play out for New England and for the world are dramatic," he said. "The differences in the world our kids and grandkids will inherit, depending on the choices we make, couldn't be more stark."