THE OCEAN covers 70.8% of the Earth’s surface. That share is creeping up. Averaged across the globe, sea levels are 20cm higher today than they were before people began suffusing the atmosphere with greenhouse gases in the late 1800s. They are expected to rise by a further half-metre or so in the next 80 years; in some places, they could go up by twice as much—and more when amplified by storm surges like the one that Hurricane Sandy propelled into New York in 2012. Coastal flood plains are expected to grow by 12-20%, or 70,000-100,000 square kilometres, this century. That area, roughly the size of Austria or Maine, is home to masses of people and capital in booming sea-facing metropolises. One in seven of Earth’s 7.5bn people already lives less than ten metres above sea level; by 2050, 1.4bn will. Low-lying atolls like Kiribati may be permanently submerged. Assets worth trillions of dollars—including China’s vast manufacturing cluster in the Pearl river delta and innumerable military bases—have been built in places that could often find themselves underwater.
The physics of the sea level is not mysterious. Seawater expands when heated and rises more when topped up by meltwater from sweating glaciers and ice caps. True, scientists debate just how high the seas can rise and how quickly (see Briefing) and politicians and economists are at odds over how best to deal with the consequences—flooding, erosion, the poisoning of farmland by brine. Yet argument is no excuse for inaction. The need to adapt to higher seas is now a fact of life.
Owing to the inexorable nature of sea-swelling, its effects will be felt even if carbon emissions fall. In 30 years the damage to coastal cities could reach $1trn a year. By 2100, if the Paris agreement’s preferred target to keep warming below 1.5°C relative to preindustrial levels were met, sea levels would rise by 50cm from today, causing worldwide damage to property equivalent to 1.8% of global GDP a year. Failure to enact meaningful emissions reductions would push the seas up by another 30-40cm, and cause extra damage worth 2.5% of GDP.
In theory minimising the damage should be simple: construct the hardware (floodwalls), install the software (governance and public awareness) and, when all else fails, retreat out of harm’s way. This does not happen. The menace falls beyond most people’s time horizons. For investors and the firms they finance, whose physical assets seldom last longer than 20 years, that is probably inevitable—though even businesses should acquaint themselves with their holdings’ nearer-term risks (which few in fact do). For local and national governments, inaction is a dereliction of duty to future generations. When they do recognise the problem, they tend to favour multibillion-dollar structures that take years to plan, longer to erect, and often prove inadequate because the science and warming have moved on.
As with all climate-related risks, governments and businesses have little incentive to work out how susceptible they are. Some highly exposed firms are worried that, if they disclose their vulnerabilities, they will be punished by investors. Governments, notably America’s, make things worse by encouraging vulnerable households to stay in harm’s way by offering cheap flood insurance. More foolish still, some only reimburse rebuilding to old standards, not new flood-proof ones.
However, there are ways to hold back the deluge. Simple things include building codes that reserve ground levels of flood-prone buildings for car parks and encourage “wet-proofing” of walls and floors with tiles so as to limit the clean-up once floodwaters recede. Mains water, which is desirable in its own right, may stop people without access to it from draining aquifers, which causes land to subside; parts of Jakarta are sinking by 25cm a year, much faster than its sea is swelling. If more ambitious projects are needed to protect dense urban centres, they ought to be built not for the likeliest scenario but for the worst case, and engineered to be capable of being scaled up as needed. The New York region has funnelled $1bn out of a reconstruction budget of $60bn to such experiments in Sandy’s wake.
Authorities must also stop pretending that entire coastlines can be defended. Unless you are Monaco or Singapore, they cannot. Elsewhere, people may need to move to higher ground. Bangladesh, for instance, is displacing 250,000 households.
All this requires co-ordination between different levels of government, individuals and companies, not least to prevent one man’s levee from diverting water to a defenceless neighbour. Market signals need strengthening. Credit-raters, lenders and insurers are only beginning to take stock of climate risks. Making the disclosure of risks mandatory would hasten the process. And poor, vulnerable places need support. Just $70bn a year of the $100bn in pledged climate aid to help them tackle the causes and impact of global warming has materialised. Less than one-tenth of it goes to adaptation. This must change.
Open the floodgates
Actuaries calculate that governments investing $1 in climate resilience today will save $5 in losses tomorrow. That is a good return on public investment. Rich countries would be foolhardy to forgo it, but can probably afford to. Many developing countries, by contrast, cannot. All the while, the water is coming. ■