The Seal Rocks

In a trackless pine forest by the shore of the Baltic Sea in Sweden is a largely forgotten landmark in the history of sea level change.

seal rock1

In the 16th century there were no trees here, this elephant-sized rock was almost submerged by the sea and seals sunbathed on the top in the brief Nordic summers. (…It was rediscovered, after some great detective work, by Swedish sea level expert Martin Eckman in 2012)

The puzzle around the Baltic Sea, like here on the Iggon Peninsula about 175 kms (110 miles) north of Stockholm, is that the land is rising at one of the fastest rates in the world of almost a centimetre a year in some places, more than offsetting global sea level rise.

In the early 18th century Swedes knew that river estuaries were always getting shallower around the Baltic Sea, ports had to be dredged, whole coastal towns had shifted inland since Viking days.

But they had no idea why – some Christians even speculated that it was a lingering sign of Noah’s Flood, with the water still gurgling away somewhere into the ground. It took until the 19th century for scientists to work out what was really going on – the entire Nordic region has been rebounding since the end of the last Ice Age 10,000 years ago lifted a vast weight of ice off the land, like a mattress slowly regaining its shape after you get up.

The sea level fall conundrum drew experts from across Europe to the low-lying Baltic coast.


Sweden’s Anders Celsius, most famous for inventing the temperature scale of his name and who was a professor of astronomy at Uppsala University, decided to figure out at least the rate of change. But he of course had a problem – in the early 18th century there were no benchmarks.

So he then struck on the idea of tracking down “seal rocks” – rocks whose tops poked out of the sea and where seals used to bask. When close to land, these were valuable bits of real estate in the 16th century since hunters could sneak up on unwitting seals lolling in the sunshine so the rocks were often marked on maps. The rock above was one of those Celsius identified – it was owned by a farmer, “Rich Nils”, in the mid-16th century on what was then the island of Iggon (Sea level fall has since connected the island to the mainland). Celsius visited in 1731 and knew that the top of the rock must have been just above sea level to be attractive to seals in Rich Nils’ time.

This is what the view would have looked like for a seal in the mid-16th century (ok, try to forget the trees, the leaves, the moss, and the fact that the sea is nowhere near):

seals eye view

By the time Celsius visited no seal could have climbed the rock since the water had sunk to around the base. And no self-respecting seal would even dream of climbing it now – the bottom is probably about five feet (1.5 metres) above sea level and maybe 10 metres from the sea.

So this was Celsius’ drawing – it doesn’t look much like the rock at the top but it may be the angle the photo was taken at, or perhaps Celsius wasn’t great at drawing and was just making the point? Either way, no other rock matches the 16th century maps of Rich Nils’ land, according to Eckman (…and my own wanderings around that bit of the forest).


Sea level in 1731 was at E-F and Celsius reckoned that in the 1563 it was at C-D, an estimated fall of 237 cms in 168 years, or an annual decline of 1.4 cms. That’s a bit of an overestimate (0.8 cm is now the accepted rate), but amazing based on 16th century maps.

(Even now, locals say that Rich Nils buried a pot of gold and other coins on Iggon: some have even used metal detectors to try to find it around a dip in the ground that may, or may not, be the cellar of his home).

To check out Celsius’ estimates, boatman Sture Sundin helped by taking me out to Lovgrund island to the south of Iggon, where Celsius had a mark scratched into a rock in 1731 as a benchmark to help later generations judge the Baltic Sea level fall. You can see Sture above “1731”, and subsequent dates cut as the water fell, below:

celsius rock sture 2

So we weren’t as scientific as Celsius – our main bit of expert equipment was a 2 metre folding ruler that Sture brought along from his garden.

Still, as you can see (below) the water is almost exactly 2 metres below the 1731 mark – an average of a fall of 0.7 centimetres a year over 282 years to 2013. That’s pretty close to the real estimate, even though our measurements didn’t take account of the state of the tide, which doesn’t vary a lot in the Baltic, and maybe the rock face isn’t quite vertical, etc).

Sture Sundin shows the Celsius Rock has risen about 2 metres since 1731, the opposite of sea level rise in the Baltic Sea

Sture Sundin shows the Celsius Rock has risen about 2 metres since 1731, the opposite of sea level rise, in the Baltic Sea

So the Baltic area is one of the few places in the world where the land is rising faster than sea levels – other parts of the Arctic are also rising.

But even in Sweden, local authorities are wondering if they have to worry that the global rate of sea level rise will ever catch up with the local rate of land rise about 80 cms a century. That’s a big jump from the current worldwide rate of 30 cms a century, but not unthinkable if sea level rise accelerates to the upper end of climate scientists’ scenarios, of about a metre by 2100.

So even in the gloomiest cases of sea level rise, the Baltic region will be one of the few places where coasts won’t suffer much, if at all.

Pacific islands could be helped by MIT infra-red maps

Vaitupu is a tiny low-lying island of 1,600 inhabitants in the Pacific — part of the island nation of Tuvalu (red dot, left) — and one of the first places studied by a mapping project at the Massachusetts Institute of Technology (MIT) to expose invisible risks.

The OpenIR project used infra-red images that could help planners with everything from disaster relief to coping with sea level rise.

Arlene Ducao and Ilias Koen, co-principals of the inspiring DuKode Studio, developed Vaitupu maps (below) from satellite images as part of an project (link to the final paper here) for a class Arlene and I attended run by the brilliant cyberscholar and activist Ethan Zuckerman. Vaitupu covers about 5.6 sq kms.

Arlene says the idea is that the maps “pop” — by using different infra-red filters they suddenly highlight the exact extent of things that are invisible to the naked eye, including hard surfaces (pink in the left-hand image) like roads or buildings that floods will run off.



Or they can highlight vegetation (red, right):



Or water (blue, left)



Knowing such factors can help emergency workers help plan relief efforts for a tsunami, a cyclone or an earthquake. They could also set benchmarks against which we can judge sea level rise and other impacts of climate change. My recommendation: get OpenIR!


Can art give clues to sea level rise?

Paintings by the Norwegian artist Edvard Munch often give you a sinking feeling (see “The Scream”, left). But can art give clues to sea level changes?

Masterpieces by Canaletto and Bellotto in the first half of the 18th century have been used to document the subsidence of Venice, relative to its lagoon. But might paintings from past centuries be used as informal gauges elsewhere to show the rate of ocean rise? (…has anyone tried?)

For fun, here’s a comparison that highlights some of the problems.

Below is “Melancholy” painted by Munch in 1892 by the fjord in Aasgardstrand, the village in southern Norway where he lived, and at a time when photographs were still rare:

The dark shoreline seems to be seaweed with a thin wavy line along the beach that suggests a high tide mark. Below is a photo I took today of roughly the same place (I couldn’t find a sad-looking guy: he was probably looking even more morose indoors since it was pouring with rain).

Art experts at the house where Munch lived say that the rock on the right is the same as the big one in the painting — the smaller ones have been moved with reconstruction along the beachfront.

At first glance it looks like the sea has risen, right up to the large rock — it hasn’t. In the bottom photo it’s simply nearer high tide. Also, the land in south Norway is rising — maybe 30 cms a century — outstripping any effect of sea level rise since Munch was here. (The land is still rebounding after the end of the Ice Age 10,000 years ago removed a vast frozen weight).

So this simply shows some blindingly obvious objections — artists often aren’t trying to paint an exact scene…in the painting it might be low tide, high tide, etc…and changes in sea levels — an average 17 cm rise in the 20th century, according to the U.N. panel of climate scientists — vary locally.

Still, if sea levels rise as much as many experts fear this century, old masterpieces might get dusted off as evidence — and might be far more convincing to ordinary people than experts talking about tide gauges.




Rio summit: vague on climate change and sea levels

World leaders at the U.N. Earth Summit in Rio de Janeiro said a lot of the right things about climate change and sea level rise (and many other aspects of how to promote economic growth that doesn’t damage the environment) — except details of what to do.

The final document at the June 20-22 summit was widely criticised as too much aspiration and too little action. That’s a shame for a once-a-decade summit attended by about 100 heads of state and government.

For a flavour, try some of the main references to sea levels and climate change in the leaders’ document, “The Future We Want”.

There’s this elegant get-out-of-jail phrasing about climate change: “We reaffirm that climate change is one of the greatest challenges of our time, and we express profound alarm that emissions of greenhouse gases continue to rise globally.” (…i.e. the alarm is only about the ‘global’ problem, not about rising emissions “by my country”).

How to tackle global warming change is of course being negotiated under the U.N. Climate Convention, but shouldn’t a big summit should give a clearer sense of the way forward?

And then this paragraph about sea levels: “We note that sea level rise and coastal erosion are serious threats for many coastal regions and islands particularly in developing countries and, in this regard, we call on the international community to enhance its efforts to address these challenges.” (…no real hint of how, what, when.)

And the section about small island developing states (SIDS) says: “Sea-level rise and other adverse impacts of climate change continue to pose a significant risk to SIDS and their efforts to achieve sustainable development and for many represent the gravest of threats to their survival and viability, including for some through the loss of territory.”

And finally: “We emphasize that adaptation to climate change represents an immediate and urgent global priority.” (again, a ‘global’ priority lets a lot of people off the hook).






Sea levels to rise for centuries (…even with U.N. temperature limits)

Oceans will keep rising for centuries, perhaps reaching 1.5 to 4.0 metres (5-13 feet) above current levels by 2300 even if the world achieves a U.N. target for limiting global warming, according to a new study.

Melting ice from Greenland and Antarctica, together with the fact that water gets bigger as it warms, will keep pushing up sea levels, they said in this week’s edition of the journal Nature Climate Change.

If true, even the study’s “best estimate” of a 2.7 metre rise by 2300 would be disastrous for many coastal societies, cities and even entire nations — Tuvalu’s highest point is 4 metres above the Pacific Ocean.

As you’d expect, the paper has some giant caveats — “It remains open, however, how far the close link between global sea level and temperature found for the past will carry on into the future,” according to the scientists at German, Dutch and Finnish research institutes.

Still, it’s an interesting stab at the problem.

The authors note that more than 190 nations agreed in 2010 at a U.N. meeting in Mexico to limit temperature rises to below 2 degrees Celsius above pre-industrial times — viewing that as a threshold for “dangerous” changes such as more droughts, floods and rising sea levels. That 2C goal is ambitious since temperatures have already risen by about 0.8 degree C and world greenhouse gas emissions are rising.

Yet even 2 degrees C is too much for the oceans, the experts reckon.

“A 2 °C warming limit…would probably lead to many metres of sea level rise in the coming few centuries and would maintain rates of sea level rise higher than today for many centuries,” they wrote. Above the 2 degree Celsius limit, sea levels would rise even more.

A stricter limit of 1.5 degrees Celsius, advocated by small island states and the poorest nations, would help a lot, they reckon. And Bolivia’s left-wing government refused to sign up for the 2 degree target, saying that anything more than 1 was too much (a political paradox to have a landlocked country advocating a policy that would do most to help the oceans?).

The U.N. panel of climate scientists has given wide ranges for sea level rise, partly because the response of ice sheets is so hard to predict. It estimated in 2007 that oceans would rise by between 18 and 59 cms by 2100, reckoning even in its basic scenarios that Antarctica would withdraw water from the oceans because more snow would fall on the frozen continent.

The new study puts this century’s rise at about a metre (higher than the U.N. panel, in line with a lot of estimates since 2007). And a lot of the current warming of the atmosphere will take decades to affect the deep oceans, it says, based on past “semi-empirical” knowledge of the oceans’ response.

“Sea-level rise is a hard-to-quantify, yet critical risk of climate change,” Michiel Schaeffer of Climate Analytics and Wageningen University, lead author of the new study, says in a release by the Potsdam Institute for Climate Impact Research. “Due to the long time it takes for the world’s ice and water masses to react to global warming, our emissions today determine sea levels for centuries to come.”

(Photos: top – Coast of Maine, U.S., 2012; lower – Antarctica, near Norway’s Troll station, 2008)


U.S. coasts — California faces fast sea level rise: “hot spot” already in Atlantic

Much of California could suffer sea level will rise of about a meter (39 inches) this century — faster than the global average — while there is already a “hot spot” of sea level rise on a densely populated 1,000 km (600 mile) strip of the east coast, studies show.

The separate reports are new evidence that city planners, governments, engineers etc will have a tangle of priorities and competing claims for money if sea level rise accelerates since the effects won’t be the same everywhere.

The west coast projections, in a report by the U.S. National Research Council, are bad news for low-lying areas such as San Francisco airport or Venice Beach (below) in Los Angeles, which might look ever more like the flood-prone Italian city of the same name.

And a recent acceleration of sea level rise along a strip of the east coast, to 3 to 4 times the global average (of about 3 mm a year), is affecting cities including New York and Boston, according to scientists writing separately in Nature Climate Change.

A slowdown of the Gulf Stream system that sweeps warm water northwards in the Atlantic seems to be the cause. (…of course that doesn’t mean that seas off the east coast can keep on rising at such fast rates throughout the century).


The west coast report also says that seas will rise by less than the world average in Northern California, Oregon and Washington. Yet other worries are that a big earthquake could cause subsidence that lowers the coastline by a meter in one gigantic jolt.

“Sea-level rise is uneven and varies from place to place. Along the U.S. west coast it depends on the global mean sea-level rise and regional factors, such as ocean and atmospheric circulation patterns, melting of modern and ancient ice sheets, and tectonic plate movements,” the council said.

For the California coast south of Cape Mendocino — a spot north of San Francisco — the committee projects that sea level will rise by 42 to 167 centimeters by 2100 (so a meter is about the middle of the range). For Washington, Oregon, and California north of Cape Mendocino, sea level is projected to rise by 10 to 143 centimeters by 2100, it said.

On the east coast, scientists write that “Our analyses support a recent acceleration of sea level rise on about 1,000 km of the east coast of North America north of Cape Hatteras. It said the hotspot was “consistent” with sea level rise expected by a slowdown of the Gulf Stream.

The report about California projects that world sea level will rise by 50 to 140 centimeters by 2100, a lot more than the estimate of 18 to 59 cms by the U.N. panel of climate scientists in 2007, which also said there was a possible extra of up to 20 cms if there are big changes in ice sheets in Greenland or Antarctica.


North Carolina and King Canute

North Carolina’s Senate passed a bill this week limiting how far the U.S. state can project sea level rise — watered down from a much ridiculed draft that sounded like it might have been written by King Canute, his toes getting wet as he tried in vain to order back the rising tide on a beach in England in the 11th century.

Developers in the state have been worried by some scientific studies that suggest that sea level rise might accelerate to a metre (39 inches) or more by 2100 — forcing a redefinition of many coastal areas as flood zones, rather than prime sites for beachside condominiums. A group known as NC-20 — which says “coastal development is the primary economic engine” of the state’s 20 coastal counties — has been especially sceptical about sea level rise. The evidence for an acceleration is simply too vague, they say.

The Senate’s final version, passed on Thursday, says that:

“Historic rates of sea-level rise may be extrapolated to estimate future rates of rise but shall not include scenarios of accelerated rates of sea-level rise unless such rates are from statistically significant peer-reviewed data and are consistent with historic trends.”

That’s a bit of a shift from an earlier head-in-the-sand draft that virtually outlawed sea level rise:

“…rates shall only be determined using historical data, and these data shall be limited to the time period following the year 1900. Rates of sea-level rise may be extrapolated linearly to estimate future rates of rise but shall not include scenarios of accelerated rates of sea-level rise.”
All of this sounds reminiscent of King Canute (above), a Viking and 11th century King of England, who in some accounts took his throne to the beach and told the tide not to rise, perhaps to show his courtiers that even kings could not rule over nature. (He has got a bad press ever since, with many commentators, perhaps wrongly, accusing him of arrogance).
A gap in the North Carolina logic is still that projections have to be “consistent with historic trends”. (While happily grazing day after day in a field, how many millions of cows raised for beef have decide, based on historic trends, that farmers have their best interests at heart?)

And the North Carolina Senate omits to notice that sea level rise has already picked up.

“There is strong evidence that global sea level gradually rose in the 20th century and is currently rising at an increased rate, after a period of little change between AD 0 and AD 1900. Sea level is projected to rise at an even greater rate in this century,” the U.N. panel of climate scientists said in a 2007 report.


It says sea levels rose 17 cms in the 20th century (1.7 mm a year) but picked up to about 3 mm a year since about 1993. It projects a rise of between 18 and 59 cms this century, without counting the possibility of an accelerated thaw of Greenland or Antarctica that might add, in one U.N. scenario, up to 20 cms.
And since 2007, many scientists have become more worried by the giant ice sheets and reckon that seas could rise by perhaps a metre by 2100.
Despite wide ridicule, the North Carolina debate is a great illustration of the global dilemma — how do you plan for sea level rise when societies have to pay for education, pensions, healthcare, roads, etc?
Should societies plan for the worst — and risk gigantic, unnecessary investments in coastal infrastructure? Or should they ignore it and hope for the best — and risk far more damaging losses?
Rather than talk about 2100, a sensible way to start would be to make low-cost decisions to cope with early signs of sea level rise — worse storm surges and erosion. Roads along a coast, for instance, should be sited inland with spurs down to the coast so they don’t get entirely washed away in a storm. Try to build homes that can flood without getting ruined.
Because, after all, even Kings can be wrong.
(top photo: port of Wilmington, North Carolina, taken by U.S. Dept of Transportation; Map by U.S.



Welcome to

Welcome to; a site trying to make sense of how fast the ocean levels will rise because of climate change, and what the world can do about it.

In the worst case this century, rising seas could force tens of millions of people from their homes in low-lying regions from Bangladesh to Egypt, from Sydney to Miami, and swamp island nations such as Tuvalu or the Maldives. In the best case, the rise will manageable, in most areas.

This site will try to figure out the scientific projections and connect coastal communities with planners, engineers and architects — anyone who’s interested.

Sea levels rose 17 cms (7 inches) in the 20th century, according to the U.N. panel of climate scientists, and have recently increased to about 3 mm a year — a rate of 30 cms over a century. The panel projects a rise of 18 to 59 cms this century, before taking account of a possible acceleration of the melt of ice sheets in Greenland or Antarctica. By one estimate by the panel, that could add up to 20 cms.

But the uncertainties about Antarctica and Greenland are enormous. U.N. Secretary-General Ban Ki-moon has said that ocean levels could rise by 2 metres at the worst by 2100. And sea level rise won’t just magically stop at 2100; it will keep going.

The picture above shows the shattered Wilkins Ice Shelf in Antarctica in 2009 — the breakup of ice on the ocean around the frozen continent could be removing a buffer that means that glaciers behind will flow more quickly into the sea, meaning ever more water added to the oceans.

So how can you plan for something that might just be a few cms or a massive 2 metres? In the worst case, how many people will have to move inland, or even abandon their homes on coral islands? Will rich nations be building dikes like the Dutch? Or barriers such as across the Thames or in the Venice Lagoon? How much will all that cost?

This site will try to show how. Please get in touch.