Medium: Why build maps of predicted sea level rise?

Ben Strauss: Climate change is often discussed in terms that make it distant in time and place, and abstract and statistical. And that makes it hard for people to engage or grasp the issue. My goal in developing our online maps and tools has been to share climate change as a local issue that matters for specific homes and families.

What’s been the most surprising or notable reaction to the maps?

A lot of artists have used the maps for public art projects or modifying images in ways that are really interesting. We’ve also made presentations to a lot of local officials and coastal stakeholders. Many times, we saw the scales lift from their eyes. They can’t believe what the maps show. I’ve heard stories of diplomats who saw maps of their countries like this for the first time and were profoundly moved and understood the stakes of climate change for their countries in an entirely new way.

Many of the people to whom I’ve shown your maps simply don’t believe them.

This change is unprecedented in human history. None of our institutions or beliefs are conditioned on dealing with any problem like this one, so it’s not surprising that it’s hard for people to digest. We don’t have a near or useful precedent, so it is a big challenge to get through to people.

There is an academically established tendency for climate scientists to understate danger.

How do we know how much sea level rise to expect?

One of the ways we know is by examining the deep geologic record. Over the last couple million years, the planet has cycled through ice ages and warm intervals between them. There are a variety of ways we can estimate how warm those past warm periods were, and how high the sea level got. And when we do that, we see that sea level is extremely sensitive to temperature. That science is continually under further development, so like with any true science there’s never a final word. But one paper two years ago found on the order of seven or eight feet of sea level rise per degree Celsius warming. Other research suggests much greater sensitivity, maybe 10, 15, or 20 feet of sea level rise per degree Celsius warming.

And how do we match CO2 levels to temperature?

​Past regional and global temperatures can be inferred from different isotope ratios in ancient microfossils and a range of other ​substrates. CO2 concentrations are measured in air bubbles trapped in ancient ice samples. Multiple independent methods have been checked against each other, providing a reasonable degree of confidence.

Where is the greatest uncertainty in the models?

I’d say the maximum uncertainty is in the timing. If I were to dump a freezer full of ice out in the middle of Miami, anyone on the planet could tell you in an instant how much of that ice is going to melt. All of it. But it would take a great deal of measurement and scientific expertise to tell you how many ounces of ice would melt each minute and exactly when the ice would finish melting. That is the task facing scientists trying to give projections over the coming decades. Every ton of carbon we put into the atmosphere is like unplugging another freezer full of ice. It doesn’t instantly melt. But the number of freezers we’ve already unplugged is enough to wreck many important coastal cities in the world.

Do climate scientists tend to be conservative in their estimates?

There is an academically established tendency for climate scientists to understate danger. The scientific community tends to be reluctant to be drawn into public argument, or be accused of alarmism. The tragedy of this field is that it’s become so politicized in the United States. I think climate scientists in general really want to share their information and want to be heard by the public, but sometimes the messenger gets shot.

What’s an example of the community being conservative?

The IPCC [Intergovernmental Panel on Climate Change], which is the consensus voice of the global climate science community, historically has ignored most contributions from Antarctica because we didn’t have the science to make a reasonable forecast from Antarctica. Therefore it was just left out, or there was a small footnote that said, “By the way, true sea level rise might be greater because we’re basically not counting Antarctica.” Now, Antarctica holds more than three-quarters of the sea level rise potential in the world. The last IPCC report did more explicitly include Antarctica but we’re just beginning to understand Antarctica a little bit better. We’re going from thick ignorance to early understanding.

What is the most common misconception that you’ve encountered about climate change?

I think the most common misconception about climate change is that scientists disagree whether it’s happening and if humans are causing it. There is extreme consensus on this issue. Like there is for gravity. Now we don’t know everything about gravity. We are still learning. And the same is true for climate change, but it really is not the subject of scientific debate around its fundamentals, or whether it’s happening, or whether it’s us, or whether it’s dangerous.

The tragedy of this field is that it’s become so politicized in the United States.

Why focus on maps of sea level rise, and not drought or other effects of climate change?

I chose to focus on sea level rise because you can localize in advance where the problem is going to be. I think it is uniquely suited for communicating around climate change more broadly. But, other problems can also be localized in different degrees. The increase in weather extremes is different in different places. Risk of drought or inland flood is different in different places. Same for wildfires. And sometimes you might be able to localize a problem by, for example, making a forecast for increased wildfire risk over a broad region and then intersecting that with data on the location and the characteristics of forests within that region in proximity to development. Then you might be able to say something much more local.

Sounds like you have another map cooking.

Stay tuned.

What do you think is the most dangerous consequence of climate change?

In the near term, the most dangerous threat of climate change is drought and disruption of agriculture, diminishment of food security and political instability and conflict.

What global temperature rise have we irreversibly locked in right now, assuming we never pull CO2 out of the atmosphere?

If we could get to zero emissions tomorrow, I bet we’d end up with maybe a touch less than 1.5 degrees Celsius. We’ve already warmed by more than 1 degree Celsius from a pre-industrial baseline and some amount of warming is being masked by aerosols that are the result of fossil fuel combustion. And that number is probably a few tenths of a degree Celsius. I don’t think it’s well established.

How does that masking work?

It’s a tragic secret about climate change. When you burn coal you actually are producing more cooling power than warming power. Burning a ton of coal cools the earth more than it warms the earth but only for two weeks. The cooling power then rains down out of the atmosphere and the warming power lasts for centuries and millennia. If we were to stop burning all fossil fuel tomorrow, within a few weeks we would lose the shade from all of those dirty particulates and aerosols in the atmosphere that are helping to shade us and we would see a spike in global temperature.

When you say that we’ve locked in 1.5 degrees Celsius, you’re saying that we’ve locked in something like nine feet of sea level rise?

In our fairly conservative analysis, yes.

One of your recent paper abstracts includes the claim that “Without protective measures, revised median relative sea-level projections would by 2100 submerge land currently home to 153 million people.” What kind of rise does that correspond to?

That corresponds to around five feet of sea level rise and that’s using data that grossly overestimate elevation and therefore underestimate the threat. You can probably double or triple the number of affected people. A lot of people live on really low coastal land around the world, especially in Asia. Also, this forecast is of land that would be permanently inundated, not just temporarily flooded.

So we’re talking a displacement of maybe a half a billion people by the end of this century?

Possibly. I should add that a really important paper came out a few weeks ago that showed that the rate of ice loss from Antarctica has tripled over the last couple of decades. We do seem to be waking this sleeping giant. If that kind of acceleration were to continue then we would be talking about on the order of 10 feet of sea level rise by the end of this century.

If we neglect the tripling of the Antarctic melting speed, when is a conservative estimate for when we’ll get our 9 feet of sea level rise from the 1.5 Celsius we’ve already locked in?

I’d say 400 years. That would be quite conservative. It’s very easy to imagine it happening at the end of the next century.

How irreversible is this sea level rise?

There’s some amount of sea level rise that we wouldn’t be able to avoid even by somehow cooling down the planet, because you have these giant ice sheets on Greenland and Antarctica flowing out into the ocean through outlet glaciers, and right now the ice dams and plugs that are blocking those outflow glaciers are disintegrating. Once you destroy those plugs the ice is going to flow out into the ocean even if we cool things down again. It’s just gravity. And we don’t know exactly what the point of no return is for different ice sheets and glaciers.

I’m partial to Boston, and it seems to be in particular danger.

Yes, I think Boston is in more danger from sea level rise than almost any other city in the country. South Florida gets all the press, and it deserves a lot of press, but we overlook the threat to Boston.