By Dr Anne Wheldon, Ashden
Soaking up the problem…
When I read the recent IPCC summary update and supporting documents on the science of climate change, I was struck by how much the sea buffers us from the impact of climate warming.
Part of this buffering is through absorbing carbon dioxide (CO2), the main driver of climate warming, and so removing it from the atmosphere. From measurements of CO2 concentrations, the IPCC estimates that around 30 percent of CO2 emitted to date from human activities has ended up in the oceans.
But, crucially, the sea also absorbs heat. The IPCC is now more than 99 percent certain that the top 700 m of the oceans have warmed during the past 40 years, and is also more than 66 percent certain that ocean warming continues down to at least 2 km depth. They estimate that 90 percent of the energy increase in the climate has been stored in the oceans.
Without the sea, we would probably have fried by now.
…brings other problems
But this protective effect of the sea brings other problems. Increasing CO2 concentrations make sea water more acidic, with serious impacts on marine life. And water expands as it gets warmer, making sea levels rise.
Measurements reported by the IPCC show that sea levels have risen by about 18 cm over the past century, and at a rate that is very likely to be the highest in the past two millennia. Melting glaciers and ice sheets, another result of climate warming, contribute to this rise.
And it’s not just the average rise that is of concern: the IPCC also found it likely that extreme, high sea level events have increased as a result of the warming climate since 1970.
Sea temperature lags behind air temperature
Sea temperature – and hence sea level – responds more slowly than air temperature to changed energy flows. Just think how long it would take to heat a bath of water by switching up the central heating thermostat.
So what might happen to sea level in the future?
The IPCC has modelled climate up to the year 2100, using four different scenarios of how concentrations of greenhouse gases might progress. In their most optimistic scenario*, annual emissions of greenhouse gases start to reduce from around 2025, and net emissions are close to zero by 2100. Under this scenario (and within a wide margin of uncertainty), global surface temperature peaks mid-century at about 1oC above its 2000 level, and by 2100 is very slowly decreasing. Sea level, on the other hand, rises continuously and is about 45 cm higher by 2100. At the other extreme, annual emissions continue to increase year-on-year, so by 2100 they are three times their 2000 level. Global temperature is around 4oC higher, sea level is 75 cm higher and both are increasing rapidly.
So even under a scenario where the air temperature has stabilised, the sea continues to rise, because of its slower response.
People and power stations near the coast are most vulnerable
Some people might not be concerned by a 45 to 75 cm rise in sea level this century, but I find it alarming.
My main concern is that sea water will be gradually seeping into the land, making groundwater too saline for human consumption and agriculture, and eroding the foundations of buildings. This means that coastal land will becomes less and less useful for human habitation and food production, and coastal infrastructure will be at risk. The impact of the gradually rising sea will be compounded by the increase in extreme events, which will destroy lives, livelihoods and infrastructure like grid electricity.
And the numbers of people and amount of infrastructure at risk are sobering. Some 10 percent of the global population lives within 10 m of sea level. In some countries, particularly in Asia, the proportion is much higher – in Bangladesh nearly 50 percent of the population (that’s more than 70 million people) live below this elevation. With many people in coastal areas lacking modern energy services, the worry is whether governments will continue to invest in energy infrastructure if it is likely to be destroyed by the sea.
In addition, a large number of the world’s thermal power stations, particularly nuclear power plants, are located on the coast to make use of sea water for cooling. The new Hinkley C nuclear plant announced by the UK Government on 21 October will be on a site that is just 14 meters above sea level and about 50 meters from the coast. Like people, coastal power stations are very vulnerable to extreme events, as the Fukushima disaster has shown.
What role can local sustainable energy play here?
Ashden exists to champion and promote sustainable energy solutions that cut carbon, protect the environment, reduce poverty and improve people’s lives. The recent IPCC update only reinforces my conviction that these solutions are key to tackling climate change – and one part of this is helping to both reduce and adapt to the threat from sea level rises.
For a start, people living in low-lying areas may benefit from standalone power supplies, like solar home systems. This has already been shown in areas of Bangladesh that were struck by cyclone Sidr in 2007, where solar home systems installed by Ashden winner Grameen Shakti maintained crucial phone communications and lighting when mains infrastructure had been destroyed.
It also makes sense to increase the use of local generation on electricity grids, and so reduce dependence on large coastal power stations. Sharing out generation between different locations cuts distribution losses and shares out risk. If the generation is from renewable sources like hydro, wind, solar PV or biomass, then it also cuts CO2 emission. “Local” can be at different scales, from solar PV on individual homes, as exemplified by Ashden 2013 winner WREN, up to community-scale wind farms such as those developed by 2007 winner Ecotricity.
The IPCC will report in 2014 on the current state of knowledge about mitigating and adapting to climate change. I hope that sustainable energy will appear strongly in their analysis and recommendations.