One of the clearest areas impacted by the climate emergency is the world’s oceans. Excess heat trapped in the atmosphere by greenhouse gases spreads into the oceans which absorb around a third of all manmade CO2, and 90 percent of the excess heat created by those greenhouse gas emissions.
Along with the warm air itself, the heat absorbed by the oceans melts ice in the polar regions, raising sea levels; melting glaciers also have an effect. The expansion of seawater as it warms contributes substantially to sea level rise, perhaps accounting for as much as 40%.
Satellite radar measurements reveal an accelerating rise of 7.5 cm (3.0 in) from 1993 to 2017. Forecasting sea level rise is challenging, depending on many assumptions. The International Panel on Climate (IPCC) have a range of warming forecasts, which predict a sea level rise of up to one metre by 2100. But more recent studies using more varied scenario planning have challenged that modelling and suggested that on current warming trends the seas would be as much as two metres higher by 2100 in even the median scenario.
At higher levels of CO2 emissions, and warming sea levels will rise further. A recent IPCC reportforecast global mean sea level rise to be around 10% higher with global warming of 2°C compared to 1.5°C by 2100. This difference implies that up to 10 million more people would be exposed to related risks of flooding, saltwater intrusion and damage to infrastructure. The higher rate of sea level rise at global warming of 2°C also reduces opportunities for adaptation. And remember that the Climate Action Tracker forecast based on the Paris Conference commitments was for a temperature rise of 3°C.
The Met Office annual report on climate change found that average sea levels around the UK have risen by 1.4mm a year since 1900 – equal to a rise of 16cm (6.3ins). Their mean projection for sea level rise in London by 2100 is 60cms, with an upper estimate of 1.15 metres. UK coastal flood risk is expected to increase over the 21st century and beyond under all emission scenarios considered. “This means that we can expect to see both an increase in the frequency and magnitude of extreme water levels around the UK coastline.”
The effect of sea level rise on low-lying islands and coasts could be dramatic. As well as the direct effect and the salinization of farm lands, higher sea-levels lead to more extreme events such as flooding and storms. The International Organization for Migration (IOM) quotes Professor Myers of Oxford University who estimated that as many as 200 million people may become refugees from a combination of disruptions of monsoon systems, by droughts of unprecedented severity and duration, and coastal flooding. The World Bank suggested 140 million by 2050.
28% of Bangladesh’s 165 million people live on the coast. During the rainy season more than one-fifth of the country can be flooded at once. The number of Bangladeshis displaced by the varied impacts of climate change (eg cyclones, salt water incursion) could reach 13.3 million by 2050, according to a March 2018 World Bank report. The effect on South Asia as a whole could be as many as 40 million migrants.
Mumbai and other fast-growing coastal megacities in Asia are particularly vulnerable to climate-related flooding. Large parts of Mumbai are built on land that, 300 years ago, was mostly underwater. When the British, who took over in 1661, they connected a series of islands into a contiguous landmass and created a peninsula by filling in land gaps to connect the islands. So the city is only artificially higher than sea level. Twenty-one of the world’s 31 megacities (cities of 10 million or more) are on the coast, 13 of these are in Asia.
Pacific Islands like Kiribati are very vulnerable to sea-level rise. Kiribati is a system of islands across the Pacific, the majority of which lie a mere 5-6 feet above sea level. Kiribati could be uninhabitable in as little as 30 years, given the current pace of climate change.
In the US, research identifies 241 cities of 25,000 people or more that will require at least $10 million (£7.9 million) worth of sea walls by 2040 just to protect against a typical annual storm. Even the internet is under threat – thousands of miles of fibre optic cables are under threat in US cities like New York, Seattle and Miami, and could soon be out of action unless steps are taken to protect them.
In the UK, a report from the Committee on Climate Change (CCC) said existing government plans to “hold the line” in many places – building defences to keep shores in their current position – were unaffordable for a third of the country’s coast. In the 2080s, 1,600km of major roads, 650km of railway line and 92 stations will be at risk, the CCC found. Ports, power stations and gas terminals are also in danger. Holland, with 26% of the country already below sea-level, is working hard on adaptation technology.
There are second-order effects too. The retreat of coastal forests as sea level rises is well documented. Tidal flooding and saltwater intrusion as well as flooding and wind associated with storms can kill trees. This creates a feedback loop where vegetation no longer provides a buffer against storm surges.
The oceans don’t just soak up excess heat from the atmosphere; they also absorb excess carbon dioxide, which reacts with the seawater making carbonic acid. Increasing acidity has effects such as depressing metabolic rates and immune responses in some organisms, and causing coral bleaching. In 2016, bleaching of coral on the Great Barrier Reef killed between 29% and 50% of the reef’s coral; in 2017, the bleaching extended into the central region of the reef.
Ongoing acidification of the oceans may threaten future food chains. But it can have other surprising effects: squid populations are expected to rise because their faster breeding cycles enable them to adapt to changing environments faster than their predators. And jellyfish have experienced a population explosion in recent years.
Warming seas also change fish behaviour, impacting both the birds that feed on them and the fishing industry. Species such as cod, sea bass and king crab are expected to move further north. Fishermen in North Carolina, fishing for black sea bass, may have to travel 300 or 400 extra miles to find them. Climate change starved to death thousands of puffins in Alaska when the fish they eat migrated north with rising sea temperatures.
In our next post on climate change, we will look at effects on land. If you have views on any of the issues in this field, please do contact us and we can give you the opportunity to express them.
Written by Huw Williams, SAMI Principal
The views expressed are those of the author and not necessarily of SAMI Consulting.
SAMI Consulting was founded in 1989 by Shell and St Andrews University. They have undertaken scenario planning projects for a wide range of UK and international organisations. Their core skill is providing the link between futures research and strategy.
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