The question of exactly how bad any particular degree of climate change would be is extremely challenging to answer in advance. How much net human suffering would result from warming the planet 1°C? What about 2°C? 5°C? 10°C?
The answer to this question is important, since it helps to determine what the best course of action for humanity is. In theory, we could ban the use of fossil fuels tomorrow, shut down the world’s coal-fired power stations, park cars, ground airplanes, and start re-building the energy basis of society without the use of planet-warming sources of energy. Alternatively, we could ignore the problem for years, decades, or even centuries – allowing the planet to get ever-hotter until we completely run out of fossil fuels.
Here’s one way to simplify the problem: just think about the Greenland and West Antarctic ice sheets. These massive slabs of frozen water could raise global sea levels by 14 metres if they melted completely. That would have a gigantic human impact. Major cities like New York, Vancouver, Tokyo, and London would be seriously inundated. Whole countries like the Netherlands and Bangladesh would largely cease to exist as dry land.
Bearing in mind that we are eventually going to have to abandon fossil fuels anyhow (because they exist in finite quantities), it seems sensible to say that it is worth switching away from them early to prevent the loss of these ice sheets. That is just one of the many climatic consequences that would arise from a particular level of warming. It would be accompanied by droughts, floods, agricultural changes, species relocating, ocean acidification, loss of glaciers, and much else besides. But – to simplify – we can just think about the ice sheets. That lets us set an upper bound for how much warming we can tolerate, which in turn establishes an upper bound for how many fossil fuels we can burn.
Where exactly does that boundary lie? One suggestive fact is that the ice sheets in question formed when the atmospheric concentration of carbon dioxide was about 450 parts per million (ppm). Before the Industrial Revolution, it was at around 280 ppm. Now, it is around 392 ppm and increasing by about 3 ppm per year. Based on a very crude calculation, it may be plausible to say that if we continue on our present course for twenty years or so, we will seriously endanger the integrity of the ice sheets.
The implications of that are pretty huge. Humanity needs to substantially cut greenhouse gas pollution not over the span of 50, or 500, or 1000 years, but over the next couple of decades. Furthermore, for it to be plausible that this change will occur successfully, rich developed countries like Canada need to cut first and fastest. Thus, just by considering one likely consequence of unmitigated climate change, we can make an argument that the complacent attitude of politicians who think we can concentrate on other issues is unrealistic. If we don’t handle this problem now, and we commit those ice sheets to eventual disintegration, people living during the time of inexorable sea level rise will quite rightly view our leaders and our generation as failures, when it comes to taking the most basic precautions to respect the welfare and rights of those who will come after us.
Seas will rise up to 1.6 metres this century, researchers say
Change would threaten coasts, islands, wildlife
Alister Doyle, Reuters; Reuters
Global sea levels will rise faster than expected this century, partly because of quickening climate change in the Arctic and a thaw of Greenland’s ice, an international report said on Tuesday.
The rise would add to threats to coasts from Bangladesh to Florida, low-lying Pacific islands and cities from London to Shanghai. It would also raise the cost of building tsunami barriers in Japan.
Record temperatures in the Arctic will add to factors raising world sea levels by up to 1.6 metres by 2100, according to a report by the Oslobased Arctic Monitoring and Assessment Program, which is backed by the eight-nation Arctic Council.
“The past six years (until 2010) have been the warmest period ever recorded in the Arctic,” said the report.
“In the future, global sea level is projected to rise by 0.9 metres to 1.6 metres by 2100 and the loss of ice from Arctic glaciers, ice caps and the Greenland ice sheet will make a substantial contribution,” it added.
The rises were projected from 1990 levels.
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Around 125,000 years ago—when the IPCC thinks the Arctic was last much warmer than today—polar meltwater raised the sea level by 4-6 metres. If that happened again it would displace a billion people and inundate most of the world’s biggest cities, including New York, London and Mumbai. The chances of that are uncomfortably high—though it might take a couple of centuries—because of another Arctic surprise.
The IPCC’s prediction in 2007 of a rise in sea levels of up to 59cm by the end of this century was attended by large uncertainties over the world’s big ice sheets. Greenland’s is up to 3km (1.9 miles) deep and contains enough water to raise the sea level by 7.5 metres; the Antarctic ice sheets are much bigger and could potentially cause a 57-metre rise. In recent years they have also been monitored by satellite, with the first data obtained in 1992. Until about 2000 the ice sheets seemed to be more or less stable, with increased snowfall on their tops compensating for increased melting at the margins.
But in Greenland something has changed. The ice sheet’s recent rate of loss—around 200 gigatonnes a year—represents a fourfold increase on a decade ago. Half this melting is thought to be due to the warming atmosphere. The other half is due to warmer seawater, caused by global warming or a shift in Atlantic currents, or both. As a result, the sea is eating away the edge of the ice sheet at a faster rate. Between 2002 and 2007 the Jakobshavn Isbrae, a big glacier in western Greenland, retreated by 3km a year, shedding a total of over 36 billion tonnes of ice.
If the climate stabilises soon, the ice cap might resettle at a slightly lower mass than it has now, raising sea levels by only a few centimetres. But if the warming continues, the ice cap will continue to melt. Sooner or later, it is thought, a tipping-point would be reached when the decline would become terminal. “How long will the ice cap last?†asks Dorthe Dahl-Jensen of the University of Copenhagen, who has studied the subject in depth. “We don’t know because we don’t fully understand what determines the velocity of its ice streams.†But such a collapse has happened before. Around 15,000 years ago the Barents Sea ice sheet, which stretched from northern England to Siberia, disintegrated in perhaps less than 1,000 years, probably because of warming seas.
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.
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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.
Sea-level rises on the order of one metre—a bit above the IPCC range for 2100—will cost the world a lot. Leaving aside fatalities owing to storms and storm surges, whose effects are worse in higher seas, one estimate made in 2014 found that by 2100 the value of property at risk from marine flooding would be worth between $20trn and $200trn. The Union of Concerned Scientists, an American ngo, estimates that by that time 2.5m existing coastal properties in America, today worth $1.1trn, could be at risk of flooding every two weeks.
A massive problem for some; an existential risk for others. Atoll nations like Kiribati—average elevation less than two metres—risk losing almost all their territory to floods like that pictured on the previous page. In 2015 the president of Micronesia, another Pacific island state, described the fate of such nations in the global greenhouse as “potential genocideâ€. This, one hopes, goes too far; refugees could surely be resettled. Still, the extirpation of entire territorial states would be without any modern precedent.
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The biggest extra effect of human activity, though, may well be putting more property at risk as a more populous and richer world concentrates itself in cities by the sea. In the rich world, and increasingly in emerging economies too, the closer to the beach you can erect a condo or office block, the better. In New York alone 72,000 buildings sit in flood zones. Their combined worth is $129bn.