Yesterday, I was pointed to some fascinating maps created by National Geographic that depict the world’s new coastlines if all the ice on earth (five million cubic miles) were to melt. The scenario sees sea levels rise by 216 feet, causing drastic changes to Earth’s shorelines. The maps show both the present-day and new shorelines, as well as providing an informative timeline of ice history and it’s distribution on Earth. Click here to see the maps.
From the depicted rise in sea level, Europe sees some of the biggest changes; the Netherlands disappear and so too does the majority of Denmark. Eastern England, western France and northern Italy also suffer submergence. Those cities lost to the ocean include London, Venice, Stockholm and Amsterdam.
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| Map of Europe following a 216 foot sea level rise (National Geographic, 2013) |
Cross the Atlantic Ocean, over to North America, and the entire Atlantic seaboard is engulfed, losing cities such as New York, Norfolk and Charleston. The Gulf coast and Florida also disappear, meaning Houston, New Orleans and Miami are no more. Moving down to South America, two huge new Atlantic inlets are formed from the Amazon and Paraguay river basins.
Over in Asia, much of China, India and Bangladesh are flooded, again saying goodbye to large cities such as Shanghai, Dhaka and Hong Kong.
Australia is also heavily impacted. Much of its coastal strip has been lost to the rising ocean, proving catastrophic for the 80% of Australians living in this region. Additionally, a new sea has formed in the centre of the continent.
As for Antarctica, it is virtually unrecognisable - not surprising considering the East-Antarctica ice sheet alone contains four-fifths of Earth's ice.
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| Map of Antarctica following a 216 foot sea level rise (National Geographic, 2013) |
Of all the continents, Africa is least affected. However, the increase in temperature due to the continual carbon emissions has made Africa less inhabitable by this stage.
According to National Geographic, the time taken to reach this ice-free planet will ‘probably’ exceed 5,000 years, although ‘no one really knows’. If it does happen, however, it will be the first time that Earth has been ice-free in more than 30 million years.
The maps are interesting to look at and do help increase the public’s awareness of future sea level rise; however, they have received criticism based on their scientific grounds (Bump, 2013). For one, people have questioned where they have ‘plucked’ 216 feet from, having been unable to find this figure anywhere else. Resultantly, in comparison to other studies, it has been suggested that National Geographic have underestimated this figure. However, the U.S. Geological Survey have concluded this argument, stating that the most recent data projects a sea level rise of 206 feet; thus National Geographic have slightly overestimated. More importantly though, the quoted rise in sea level has not taken into account the thermal expansion of water that occurs under rising ocean temperatures (I mentioned thermal expansion in one of my earlier posts, 'Deadly Threat No. 1: It's getting hot in here'). This will contribute ‘between 0.20-0.63m per °C of global mean temperature increase’ (IPCC, 2013). Thus, with rising global temperatures, 217 feet is a vast underestimate for future sea level rise and this has to be kept in mind when viewing the maps.
Another thing that it fails to take into account is our ability as humans to control where sea level rise actually impacts our coastlines, this is definitely something we can manipulate if it happens at a relatively slow pace.
ReplyDeleteSee this piece here http://www.bbc.co.uk/news/science-environment-24770379 where adaptations of sea walls are controlling where flooding is taking place, with benefits for both coastal humans or wildlife. Though clearly, if 217ft of sea level rise were to occur, this would be insufficient!
However, another thought... if this amount of ice melting into our oceans were to occur, would thermal expansion be a major factor, I;m sure I've heard on numerous occasions that if substantial melting occurred then the thermohaline circulation could slow or even shut down, potentially causing global temperatures to plummet?
Yes, good point Rob. The maps do fail to consider our response towards rising sea levels, which would no doubt include a mix of hard- and soft-engineering techniques or perhaps even measured human retreat. Therefore, the amount of land loss indicated is most likely overestimated.
DeleteYour ‘managed realignment’ article is a good example of how we can work with sea level rise, instead of fighting it. By surrendering land to the sea, the flood risk to local communities will hopefully be reduced and a new area of saltmarsh created. However, it would be unrealistic to think we can do this everywhere – some people actually live on the seafront and so there is no ‘free’ land to surrender.
Regarding your last question, up until the potential collapse of the thermohaline circulation (THC), thermal expansion would remain as an influence on sea level rise, as long as greenhouse gas concentrations continued to increase. Post-collapse is where it gets interesting. Vellinga and Wood (2008) modelled the climate’s response to a THC shutdown. Land areas of the Northern Hemisphere were shown to cool but temperatures remained above pre-industrial values, except in the western fringes of Europe. Contrastingly, the Southern Hemisphere was shown to slightly warm. In general, they concluded that THC shutdown changed the sign of global warming. Where northern sea ice had been shown to retreat under rising greenhouse gas concentrations, their model saw a return of sea ice to these areas post shutdown. Thus, you would think it logical to assume that with colder temperatures, thermal expansion’s contribution to sea level rise would decrease. However, Levermann et al. (2004) have suggested that a THC shutdown can, in fact, enable thermal expansion to still play a role! In locations where North Atlantic deep water (NADW) forms today, their model indicated that following a collapse, the deep ocean would begin to warm over millennia. This is because it would no longer receive a supply of cold waters from the surface. Due to this warming, thermal expansion would still occur, contributing a slow global sea level rise of the order of 1 m.
Thus, it is possible that thermal expansion will continue to play a role in sea level following a THC shutdown or slowing. However, more directly affected will be the ocean currents and distribution of mass, both factors that influence regional sea level.