Tag: sea level

Who will rule the waves?

Cleo Paskal, whose book Global Warring was reviewed recently on Hot Topic, has been speaking in New Zealand and left her card by way of an article in the Herald.  In it she focuses on one matter raised in her book – the fate of island nations whose land becomes uninhabitable because of rising seas.  Two small islands have disappeared recently. When Bermeja, in the Gulf of Mexico, disappeared so did the large claim Mexico was making in the hydro-carbon rich waters of the Gulf. No island, no claim, says the US. (Did the CIA blow the island up?) When New Moore Island at the mouth of the boundary river between India and Bangladesh disappeared, so did the competing claims of the two countries for control.

Paskal points out that the problem of land loss potentially leading to maritime zone loss is going to come up more often in the future, especially in the Pacific, and that it is a matter of considerable importance for the inhabitants. Tuvalu is an example of particular relevance to New Zealand.

Continue reading “Who will rule the waves?”

What makes sea level rise uneven

An illuminating article by Michael Lemonick just published in Yale Environment, which I summarise here, communicates some of the developing understanding of just how uneven sea level rise is likely to prove.  It will vary greatly by region. There are a number of reasons for this.  One is that the land is actually rising in some places, including northern Canada and Scandinavia, which are still recovering from the crushing weight of the Ice Age glaciers, albeit from 10,000 years ago. Their sea-level increases are less than the global average would suggest, since their land areas are rising a few millimeters a year.   On the other hand land around the periphery of where the glaciers sat, such as Chesapeake Bay and the south of England, was squeezed upwards by the downward pressure nearby and has been sinking back by a few millimetres a year ever since, so sea level rise is greater than average in these regions. Land is also subsiding in coastal places where massive oil and gas extraction has occurred such as Louisiana.

 

A larger effect is from changes in prevailing winds, which can push water consistently toward the land or keep it at bay. The trade winds that blow west across the tropical Pacific, for example, boost average sea levels by as much as 24 inches on the western side of the ocean — in places such as the Philippines — compared with those in northern South America. If those winds shift with climate change, so would local sea levels.

Ocean currents also affect sea level rise. If the Gulf Stream were to slow, for example, that would force water to pile up behind what amounts to a partial blockage of the overturning current. That could force sea level along the U.S. coast to rise another 8 or so inches over the next century beyond the global average, given a medium-emissions scenario.

But the “gorilla in the room” according to Ronald Stouffer, of the U.S. Geophysical Fluid Dynamics Laboratory in Princeton NJ, is gravitation. The extra gravitational attraction of an undersea mountain range pulls water toward it, creating a literal, permanent bump on the surface of the sea, while the deficit of gravity near an undersea valley creates a depression in the water up above. A coastal mountain range pulls the water in its direction, raising sea level nearby. So do the massive icecaps that smother Greenland and Antarctica. They keep sea level higher than it would otherwise be for thousands of kilometers around both land masses, and correspondingly lower elsewhere.

If the polar ice sheets shrink, though – as they’re currently doing, especially in Greenland and West Antarctica –  their gravitational pull weakens and so does their hold on the surrounding water. Their loss of mass not only contributes to overall sea level rise through meltwater but also allows some of the water held by their diminishing gravitational pull to go elsewhere – including the threatened east coast of the US.  And it’s not a small effect. In Hawaii, for example, Stouffer estimates that a seven metre sea level rise caused by the disappearance of the Greenland ice sheet would have an extra two or three metres added to it. Whereas a beachfront property in Iceland would end up with more beach.

Jerry Mitrovica, a Harvard geophysicist who is working with Stouffer, comments that when he gives talks about this people don’t believe him. He doesn’t blame them. “It’s just wacky when you think about it, completely counterintuitive,” he says. “But it’s true.”

Mitrovica recalls that when he started looking at regional effects, some climate change deniers were noting that sea-level rise was happening at different rates in different regions, arguing that this proved there was no global trend, and thus no global warming. That was already a bogus argument, but now that he and others have begun investigating the gorilla in the living room, it’s even more absurd. The science is so straightforward, he says, that “if you saw that sea level was rising uniformly around the world, it would be proof that the big ice sheets are not melting.”

One wonders what the Christchurch City Council might make of all this. They’ve settled for planning for a 50 cm rise. “We’re following the Government’s advice and we’re not going out on a limb,” their spokesperson said primly.  Apart from the fact that 50 cms is now inadequate advice for the century, the dynamics of regional variation suggest that an already  complex set of considerations when planning for  future sea level rise may have to be open to even more complication. Nick Smith will surely have to descend from his high horse: “The Government is not going to consider adjusting its policy every week.”  Not that I’ve heard anyone asking for weekly adjustment – but annual reconsideration might be sensible.

The dangerous sea

This column was published in the Waikato Times on March 16.

The media has paid disproportionate attention to an error in the monumental 2007 report of the Intergovernmental Panel on Climate Change.  In a chapter surveying the possible future impacts of climate change on the Asian region the report included a prediction that the Himalayan glaciers could melt by 2035. The glaciers will certainly melt if we continue on our current course, but not as soon as that. This was a mistake which the IPCC has acknowledged and regretted. Not too bad in a volume of 3000 pages, but a mistake that shouldn’t have occurred and wouldn’t have if procedures had been properly applied.

Since then there have been regular media “revelations” claiming other errors as well. For all the fanfare with which they have been produced these have so far turned out to hinge on little more than minor technicalities. They cause much excitement in the denialist community, but they amount to nothing of consequence.

Overstatement is what the IPCC is being accused of.  But the reality is that its report is generally conservative and cautious and in one very important matter likely to have understated a real danger ahead. That is sea level rise.

 

The IPCC does predict sea level rise in the century ahead, somewhere between 18 and 58 centimetres, depending on how high the level of greenhouse gases is allowed to climb.  It sounds reassuringly manageable.  But this predicted rise comes only from a combination of thermal expansion of the oceans because of warmer temperatures, and the continued slow melting of glacier ice.  It assumes there will be no increase in the rate at which melting has occurred in the great ice sheets of Greenland and the Antarctic.

Time has passed, and it is now widely accepted in scientific circles that there is reason to expect a significant acceleration in the rate at which the Greenland and Antarctica ice sheets lose mass to the sea.  The dynamics of ice movement are beginning to be better understood, and they are not reassuring.  Those massive ice sheets are seemingly not as impervious as once thought and their melting not necessarily a slow predictable linear process. Disintegration may be a more accurate word than melting.

If the IPCC predictions are too cautious, what level of rise is now being considered likely in this century?  One metre say some.  Others say that’s still not allowing sufficiently for the acceleration likely to build, and recommend planning for a two metre rise.  James Hansen of NASA is prepared to consider five metres as a real possibility, though he doesn’t offer that as a prediction..

Of all the predicted impacts of climate change, sea level rise is the one that I find most unnerving.  Its effects on human populations are distressing to contemplate.  The deltaic nations such as Egypt, Vietnam, Bangladesh and Myanmar will be badly hit. Some atoll nations will disappear. Countries with large low-lying coastal plains, such as the US, China and Brazil will be faced with tremendous disruption. Some great cities will be severely threatened, including Miami, New York, Tokyo and Amsterdam. It won’t be all that straightforward in New Zealand for that matter – a one metre sea level rise would put Tamaki Drive under water for example.

And it’s not the kind of damage that can be undone.  How could we get water to return to the ice sheets?  That’s why it is so important that we stop it happening in the first place. Any suggestion that a minor error in the IPCC report has somehow put the urgency of that task into question is out of touch with reality.

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It is likely that this is the last in the series of columns I have been invited to write for the Waikato Times over the past couple of years.  The columns are directed to the general public, not Hot Topic readers, but they may have been useful here in indicating what can be written in public forums. It’s well worth anyone’s effort to get the message across in newspapers.  I often wish there were more scientists writing in that medium, though I know it can be difficult to secure a space for opinion pieces. There are always the letters to the editor, which journalists tell me are popular with readers. The company there can sometimes be embarrassing, but if you’re willing to take that risk a clear statement on climate change will receive wide attention. It has been quite depressing to see in our local paper far more letters (often muddled) from contrarians than from those who take climate change seriously.

The Rising Sea

“All indications are that we should be alarmed about the future of sea level rise and should be doing something about it now.”  Orrin Pilkey and Rob Young, eminent coastal scientists, wrote their book The Rising Sea to provide substance for that alarm and to offer suggestions as to how we can plan ahead to reduce the severity of the impact of the rising sea.

The authors begin by reminding us that it’s not a distant prospect. They describe what is happening to Alaskan shoreline villages such as Kivalina and Shishmaref, atoll nations such as Kiribati, the Maldives, the Marshall Islands, Tokelau and Tuvalu, and the city of Venice, places already grappling with rising sea level.

Rising tide gauge data and an increase in coastal erosion along many of the planet’s shorelines provide clear evidence of the rising sea and of the warming of the planet. Not that the authors are simplistic about this. They recognise and discuss the function of tectonic changes and additions to or subtractions from the weight of the crust.  But there is plenty of evidence of an increase in the volume of water in the oceans, accelerating in response to global warming. Easier evidence to assemble, they note, than the measurement of global temperature trends.

Predictions of rise in the 21st century are dependent on what happens in the Greenland and West Antarctic ice sheets, an area which the IPCC 2007 report felt unable to take into its compass, other than by commenting that the contribution from both of these ice sheets may be much larger than previously assumed.  Pilkey and Young do not offer predictions, but they note that some organisations in the US have begun to make their own, quoting for example a committee in one of Florida’s counties which speaks of a minimum of 1 to 1.5 metres. They further note the work of University of Colorado scientist Tad Pfeffer and colleagues who argued in a 2008 paper in Science for a range between 0.9 and 2.0 metres, and they describe Hansen’s understanding that the non-linear response of the ice sheets could mean a level higher than that, possibly even as much as 5 metres. Shoreline retreat, of great importance to human society, is difficult to predict.  It’s not a simple or uniform matter and they discuss some of the variable regional factors which have to be taken into consideration in any assessments.   Their conclusion is that coastal management and planning should assume ice sheet disintegration will continue and a 2 metre sea level rise by 2100 should be reckoned with. They describe this as a cautious and conservative approach.  All rubbish, of course, to the noisy minority of opinion they address in a chapter on what they call the sea of denial.

The later sections of the book are concerned with the impacts of rising sea level.  First on natural ecosystems. The coastal wetlands and coral reef ecosystems have long migrated back and forth along with changing sea level and attendant shoreline movement. But they haven’t before had to simultaneously cope with massive changes in the physical environment cause by human activities.  Their future is unprecedented. The biggest global obstacle to salt marsh movement, for instance, is shoreline development and agriculture. There is often little room for them to expand inland.  Many will disappear, a loss both environmental and economic as yet recognised by few governments.  Mangrove areas have already been significantly reduced globally, most recently by clearing for agriculture and aquaculture. Poverty in the developing world leveraged by greed in the developed world is the driver of their destruction. Coral reefs are threatened by more factors than sea level rise, but their need for sunlight means that they must either grow upwards or migrate to shallower water to survive rising seas.

The authors then turn to the impact of sea level rise on humans.  The principal nation-scale impacts are likely to include loss of land, flooding, increased storm surge vulnerability, accelerated erosion, increased salinization, loss of biodiversity, loss of aquaculture and fishery, damage to marine infrastructure, and tourist decline.  The countries with the biggest problems are the atoll nations; deltaic countries such as Egypt, the Nethlerlands, Bangladesh, Vietnam and Myanmar; and countries with large low-lying, heavily developed coastal plains such as the US, Brazil and China. (As an aside I note that the severe effects of climate change on the US and China may be our best hope that they will act decisively to reduce emissions, once, that is, denialism loses its remaining traction among their lawmakers.) The book details the specifics faced by some of those countries.  In Vietnam, for example, a one metre sea level rise will displace more than a tenth of the nation’s people, gobble up 12 percent of its land area, and reduce food output by 12 percent.  Turning to cities the book notes an OECD study ranking the most vulnerable cities in the world as measured by susceptibility of property to flooding.  Half of the top ten are American, headed by Miami.

A closer look at the Mississippi delta forms the substance of a chapter.  The authors describe  various proposals to restore and protect the Louisiana coast and are sympathetic to some of them, such as wetland restoration.  But the vast and costly restoration effort now being sold to the residents of Louisiana and the rest of the US they consider misleading and dangerous.  Conditions in southern Louisiana are likely only to get worse no matter how much money is spent. Global sea level rise is coming. Coastal managers need to begin developing a plan to relocate towns in the lower delta, in ways which will keep the communities together. The delta culture may be preserved, but not in place.

The final chapter is titled Sounding Retreat.  It focuses on how Western countries need to respond to the landward movement of the shoreline.  The authors identify three responses: abandonment of the beachfront and relocation of all buildings and infrastructure away from the retreating shoreline; protection of the shoreline with seawalls, groins, and suchlike; formation of an artificial beach by bringing in new sand. All are expensive, but the latter two are temporary and suitable only for small rises in sea level. (No problem for Bjorn Lomborg who estimates a 30 centimetre rise.) The implications of each of these approaches are discussed in some detail with reference to specific examples. Opposition to relocation often comes from those with vested interests, and Florida extraordinarily still permits the construction of high rise shoreline buildings, taking over the financial obligation since insurance companies have backed away from insuring coastal properties. But the authors consider that in many cases relocation of beachfront communities will be the most effective solution, especially in view of the tremendous effort that will be needed to protect exposed cities.

We’re for it, the authors warn. Reduction of emissions will not halt sea level rise in the short term.  If we’re wise we’ll plan ahead. The constructive discussions and examples in their easily understood book will assist those who want to get an initial understanding both of the possible magnitude of what faces us and of the kind of measures we will need to take to manage it with the least distress. The book is well worth attention.

Dealing with sea level rise: retreat, defend, or attack?

As a handy follow-up to Bryan’s post yesterday about calls to plan for sea level rise of about two metres over the coming century, a new report, Facing up to rising sea levels [PDF], examines how two British coastal cities, Portsmouth and Hull, might cope. According to the Guardian coverage, Hull could become a “Venice-like waterworld” (which is a considerable challenge to my imagination) and Portsmouth a new Amalfi (ditto). Set aside the hyperbole, however, and the report — a joint effort by the Royal Institute of British Architects and the Institution of Civil Engineers — is an examination of how the cities could respond to sea level rise by building defences, managing a planned retreat, or by building out and over the sea as it rises. The results are a fascinating look at how ingenuity in the face of a severe challenge can create interesting environments — if not, perhaps, a new Venice in northeast England.