Sea Level Rise: It’s Probably Worse Than You Think

by | May 3, 2019

NYC in 2100 under extreme sea level rise scenario.

NYC in 2100 under extreme sea level rise scenario.

As you know, this newsletter is usually fairly inspiring. But this one is not (overall). And that’s because we really need to talk about sea level rise again.

Sorry, but the stakes are insanely high and everyone needs to know about this stuff!

That being said, I do end with an action you can take to help if you so choose! …Or you can just tell your friends about this mind-bending sea level rise predicament. Talking about these things and finding new ways to help together is always good.

Key Takeaways:

  • We’ve locked in about 7.5 ft (2.3 m) of sea level rise already.
  • Sea levels will likely be at least 3.3 ft (1 m) higher by 2100.
  • Last time Earth got this hot, sea levels were way, WAY higher.
  • Ice loss in Greenland and Antarctica is decades ahead of schedule. There’s been significant acceleration.

The fact of the matter is that coastal cities around the world will eventually have to make sci-fi adaptations or retreat…but I’m getting ahead of myself.

Setting the scene

Sea levels have gone up 7 to 8 inches since 1900.

Contributions came from:

  • Expansion of the ocean as it gets warmer.
  • Temperate land ice.
  • Greenland and Antarctica.

But recently, Greenland and Antarctica (the two ice behemoths) have started to chip in more and more…faster and faster. They are the X factors of sea level rise. And scientists have severely underestimated how fragile they are.

Wrapping Your Head Around These Melting Giants

Imagine an ice cube that’s over 1 mile high. Now imagine that ice cube covering all of Mexico and the United States. That’s how big Antarctica is.

It holds enough ice to raise sea levels by 188 feet (57 meters).

Antarctica is now losing 252 billion tonnes of ice each year. It takes every country on Earth combined ten days to use that much water. (Antarctica actually loses over 2 trillion tonnes each year, but makes up for most of it with gains from snowfall)

That means it’s losing ice at a rate of 3 Olympic swimming pools every second (net). That’s 6 times faster than it was 40 years ago. This is largely due to warmer ocean water.

And then there’s Greenland.

Greenland is as big as Germany, France, Spain, and Italy combined. It holds 24 feet (7 m) of sea level rise at bay in its ice. Like Antarctica, Greenland is losing ice 6 times faster than it was in the 1980s (286 billion tonnes per year now).

Scientists have been caught off guard by the rapid acceleration of ice loss. They thought Antarctica, in particular, was much more stable than it is. As they learn more about feedback loops and get more high-quality observational data from satellites, they are significantly raising their sea level rise projections from even just a few years ago.


“At every point, as our knowledge increases, we’ve always discovered that the climate system is more sensitive than we thought it could be, not less.” – Dr. Maureen E. Raymo

Ultimately, these ice giants haven’t raised sea levels by much so far, but the key thing to know is that the rate of ice loss is accelerating – think exponentially, not linearly – compounding over time. We have not seen the last of glaciers as big as Manhattan calving into the water.

As James Hansen says, “The disintegration of ice sheets is likely to be highly non-linear.”

So, if you’re keeping track, that’s about 212 feet of sea level rise in ice that’s melting at faster and faster rates, in addition to melting glaciers, and an ocean that’s expanding simply because it’s getting hotter (oceans absorb 90% of the additional heat from global warming).

…Which means it’s not a question of if we’ll get a lot of sea level rise, but how much exactly? By when? And, in the long run, how much sea level rise is already locked-in?

To help answer these questions and add some context, let’s’ take a quick look at what sea levels have done in the past under similar conditions.

What Were Sea Levels Like Last Time Earth Got This Hot?

Really f****** high.

As I’ve mentioned before, we’ve already left the atmospheric conditions under which civilization developed. And, as far as we know, we did it way faster than the climate has ever changed in the past naturally.

Luckily, it takes a little bit of time for the planet’s temperature and ice to fully react to our greenhouse gas emissions (like boiling a pot of water).

But if you look at sea levels the last time Earth was this hot or had this much CO2 in the atmosphere (see chart below), it becomes abundantly clear that we need to eliminate emissions immediately…and then suck some more CO2 out of the atmosphere to get back to safer levels…and then cross our fingers we did it before physically irreversible changes were set in motion.

Historical Sea Level Rise

(Context for “TODAY” figures: CO2 is increasing by 3 ppm each year. We’ve raised the temperature by 1°C already and are on track for 3-4°C. Sea levels are up 6 to 8 inches since the 19th century. Sources for info in chart.)

Lots of numbers in that chart…but my point here is this: The Earth has been here before. And when it was, the sea level was way, way higher.

We’ve just changed everything so quickly that it hasn’t had time to catch up yet.

“We know that in the Earth’s history when ice sheets have collapsed and sea level has gone up, we’ve had sea level rise of several meters in a century. So now, with humans changing the composition of the atmosphere much faster than it ever was changed in the past, there’s no reason to think that that couldn’t happen again.” – James Hansen

The historical precedent in that chart is terrifying.

But, lucky for us, unless current sea level rise projections keep jumping up, we don’t expect to see increases this dramatic by 2100.

Post-2100, on the other hand, is a different story.

We’ve Already Locked In 7 Feet of Long-Term Sea Level Rise (Likely More)

Say what?!?

I know, I was shocked too…nobody really talks about projections past 2100.

But if we waved a magic wand and eliminated greenhouse gas emissions today – the momentum of the damage we’ve already done (1°C warming) would eventually raise oceans by 7 feet.

7 feet of sea level rise is like the ocean swallowing up 4 California’s, 1 Alaska, 7.5 UK’s, or 6 Italy’s worth of land.

This is what my home city of Boston would look like under 7 feet of water:

Boston 7ft Sea Level Rise

This is from Climate Central’s “Surging Seas: Seeing Choices” map. Based on this scientific research.

Boston, as we know it, would cease to exist. Along with pretty much every other coastal city.

And, as we know, this is generous because, quite frankly, we’d be lucky to keep warming to 2°C, nevermind the 1°C shown in the map above.

Scientists estimate there will be about 2.3 meters (7.5 feet) for every 1°C of warming

Here’s what they found the locked-in sea levels to be for different temperature increases, and how many millions of people currently live where the ocean would eventually be.

Locked-In Sea Level Rise With Temperatures

(Grey columns show 66% confidence range.)

As you can see this is more of a social problem than it is a scientific one. We’re talking about people’s lives here.

I encourage you to plug in your city on the map above or that of friends and family. See how it transforms from 1°C of warming (where we are now) to 2°C (Paris target) to 3°C – 4°C (where we’re currently headed).

These numbers are what models/physics say will eventually happen given a certain temperature increase. There’s no way to know how quickly it actually will happen.

We still have a little time to stop and eventually reverse the warming. As you can see, there is a vast difference between the best and worst case scenarios.

Every little bit of warming we can prevent matters.

What to expect in your lifetime

No matter what, understand that coastal shorelines are going to be on the move for the rest of your life.

But exactly how far they come depends on a few things:

  • How much more greenhouse gas emissions get dumped into the atmosphere.
  • Whether any natural tipping points that lead to runaway warming are triggered.
  • How much heat the disrupted climatic system directs towards Greenland and Antarctica (above and below the ocean’s surface).
  • Just how sensitive Greenland and Antarctica’s ice sheets turn out to be.

As of today, scientists expect between 1 and 8.4 feet of sea level rise by 2100. And .5 to 2 feet by 2050 (.3 to 2.5 m and .15 to .65 m respectively).

But those are global averages. The East coast of the US, for example, will have much higher sea level rise (~33%) than the global average due to changes in Earth’s gravitational field, rotation, and ocean circulation (yes, that’s how much ice is melting). So Boston, for example, will likely have 1.4 to 11.1 feet by 2100 and .5 to 3.75 feet by 2050 according to NOAA’s latest projectionsNOAA’s full report can be found here. And here’s the data in excel if that’s your thing.

If you’re interested, you can use this fantastic sea level rise mapping tool to see the projected sea level rise by decade and emissions scenario for US coastal cities through 2100. This is the most useful one for understanding what will happen in the near term.

If we are able to really get our act together and stabilize temperatures under 2°C (~5% chance), most studies say sea level will be kept between .66 and 3.6 ft by 2100 (.2 to 1.1 m).

What does this all mean?

Between the consistent overly-conservative projections over time, an evolving understanding of how ice sheets collapse, the exclusion of important feedback loops for further warming in models, and historical sea levels rising as quickly as 4 meters per century, I personally am assuming there will be more than 1 meter of global sea level rise by 2100 (This is the “intermediate” scenario and what esteemed expert Eric Rignot expects will be the minimum SLR). I think the recent acceleration that has taken everyone off guard will continue. And that the susceptible West Antarctic Ice Sheet in particular, containing multiple meters of sea level rise on its own, will reach a point of no return in all but the most aggressive emission elimination scenarios (Hint: let’s be aggressive).

Based on the latest information, I think we’re living through the beginning of the hockey stick of sea level rise – much of which we’ve already locked-in, but much, much more of which that we can ultimately prevent by rapidly eliminating society’s GHG emissions.

To give you an idea of the speed of this disruption away from what we’re used to: NOAA examined 90 cities on the US coastline and found that most, with only 0.35 m (<14 inches) of local sea level rise, would face disruptive/damaging flooding 25 times more often by ~2040 under the “Intermediate” scenario.

So. There will be more floods. Those floods will be more damaging. And they will reach further and further inland. Nuisance or high-tide flooding will also continue to happen more frequently.

Along the way, property values will continue to decline, flood insurance will become too expensive for many, fresh water supplies will be contaminated, subways will be increasingly inundated, risk of water-borne diseases will go up, and a whole host of other issues.

No matter how much sea level rise we ultimately end up with though, millions of people will be forced to leave their homes. Where will they go?

This is a recipe for a global humanitarian crisis.

But perhaps most importantly, for this moment anyway, it means we need to wake up. And help other people wake up. Seriously. I knew sea level rise was going to be bad, and always expected it to be worse than the projections let on a few years ago, but researching for this article I was floored by how much sea level rise we’ve already locked in and how quickly it may all happen. We need to tell people what the latest science is saying in plain terms. We need to tell people what is in store for us if we don’t start getting out of our comfort zones and taking action with others to systemically eliminate emissions.

One Way You Can Take Action

There are many things you can do. But this is a clever and fun one.

This Place Will Be Water was launched on Kickstarter last year by Jon Leland (who I met in NYC a couple of weeks ago – thank you Kate and Sara for the assists and thinking of me!)

The idea is simple: put biodegradable stickers in places that will eventually be underwater with just 2°C of global warming.

So far, Jon has sent over 8,000 stickers to 500 participants in 18 countries.

People put them in influential places, like this:

This place will be water - Fenway Park

Makes you think, right?

Seeing the stickers, people will better understand how climate change could impact their community. Pictures can also be spread and tagged on social media with #ThisPlaceWillBeWater.

Some people say that we must be optimistic and hopeful in order to encourage others to take action. Others say fear is a better motivator. I think we need some of both. They each have a time and place.

As Jon puts it, “People don’t want to think about climate change because it’s scary. Well, they need to think about it. And they need to be scared.”

Jon is mailing me some stickers to put up in the Boston area. If you’d like to meet up to do that, let me know!

And if you live on the coast or know someone who does that’d be interested, definitely go to the site and get some stickers!


Read other content from the “Alarming” section or see all sections of the What on EARTH?! sustainability newsletter.

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