The planet’s oceans are vital to life on Earth: they produce more than half of the world’s oxygen and absorb 50 times more carbon dioxide than our atmosphere. The ocean also transports heat from the equator to the poles, regulating climate and weather patterns. The oceans are also home to a vast amount of wildlife, so vast in fact, that 91 per cent of the species in the oceans still await description.
The ocean is being greatly affected by rising emissions. These emissions cause water temperatures to rise, resulting in ocean acidification, increased storm intensity and ultimately, rising sea levels. The ocean’s ability to absorb carbon dioxide is also under threat, and indeed may result in the ocean’s contributing to, rather than mitigating against, the climate crisis.
And of all the catastrophic effects of the climate crisis, rising sea levels may cause the most visceral reaction among the public, conjuring up images of flooded cities, devastated societies and a global economic collapse. So, how quickly are sea levels rising, what’s being done about it, and what sort of future do we have coming?
According to the IPCC, global sea levels are both rising and accelerating, with glacier and ice sheet melting, the “dominant source” of these rises. The Ocean and Climate Platform has been working to bridge the gap between scientific knowledge and policy making. Its key objective is to ensure that the scientific messages on the interactions between the ocean, climate and biodiversity are acknowledged and taken into account by both policy makers and the general public. It also works with UNFCCC’s Ocean and Coastal Zone’s Climate Action Pathway as part of the Marrakech Partnership.
Loreley Picourt is the secretary general of the Ocean & Climate Platform, and the co-focal point for Ocean and Coastal Zones for the Marrakech Partnership-Global Climate Action Agenda at UN Climate Change.
She is clear on the realities of sea level rises that we currently face. “According to the latest IPCC report, sea level rise is predicted to be irreversible and is expected to continue over the coming centuries and millennia,” she says. “In parallel, related extreme events are expected to become more frequent and severe, causing coastal flooding in low-lying areas.”
However, the speed of this and its associated risks (such as erosion and submersion, loss of coastal habitats and ecosystems, salinization of land and groundwater) will be considerably slowed down [if] warming levels are kept below 1.5°C.”
Traditionally, so-called “hard coastal protection measures” such as sea walls and dikes, have been built to protect against rising sea levels, but as Picourt points out, these are no magic bullet. “If you build a dike, you will protect your coastal population, but it is not sustainable in any way, because every five years you will have to rebuild it.”
Another misconception is that sea level rises will affect all regions equally. As the IPCC report points out, “Thermal expansion, ocean dynamics and land ice loss contributions will generate regional departures of about ±30% around [sea level] rise. Differences from the global mean can be greater than ±30% in areas of rapid vertical land movements, including those caused by local anthropogenic factors such as groundwater extraction.” This is echoed by Picourt: “There are already notable variations across the world's coastlines due to natural and anthropogenic coastal movements of land subsidence or uplift, storm surges, topography and land uses,” she says. “For instance, Deltaic regions are particularly exposed to sea level rise, compounded with land subsidence (so-called sinking deltas) as a consequence of natural and climatic processes but also of human activities (drainage of soils, load of buildings and infrastructure in urban areas) – such as in the Netherlands and Jakarta.”
There are solutions available today, including Nature-based Solutions (NbS), such as planting mangroves and salt marshes, which not only contribute to carbon sequestration but have huge biodiversity benefits. “Ecosystem-based Adaptation and Nature-based Solutions can deliver significant co-benefits,” Picourt says. “In addition to acting as buffers to protect coastlines from storm surges and flooding, coastal ecosystems such as salt marshes and mangroves provide valuable habitats for a variety of species and contribute to carbon sequestration.”
Yet, developing Nature-based Solutions in urban area is often challenging, due to a lack of available space, particularly along valuable coastal areas. “The perceived lower efficiency of NbS compared to traditional hard protection by populations and decision-makers constitute a critical barrier to their development,” Picourt says.
For many coastal cities, the reality is now one of ‘managed retreat,’ where they reduce exposure to rising sea levels by relocating people, assets and activities away from coastal hazard zones. “In some cases, and as sea level continues to rise, managed retreat will be inevitable,” Picourt says. “There are already examples across the world of relocated assets (the coastal road in Sète, France), communities (native communities in Alaska) and cities preparing for scenarios that integrate relocation (Marina in California).”
The Sea’ties Declaration was launched during the One Ocean Summit earlier this year, and has so far been signed by 40 mayors, governors and city networks across the world. It calls for an acceleration in the transformation of cities and their territories, highlighting four priorities: the mobilisation of science and observation systems; the integration of societal issues within adaptation plans; the fostering of adaptive and hybrid solutions; and the increase of public funding and private investments for adaptation to sea level rise.
“The Sea’ties Declaration and the different workshops we conducted in the Mediterranean region and Northern Europe demonstrated that stakeholders are willing to implement transformational change for long-term adaptation,” Picourt says.
Despite the growing awareness of the need to start adapting to rising sea levels, there is a lot more that needs to be done. Finance, particularly for the Developing World, remains a huge issue. While a managed retreat may be possible in the US or France, many developing countries simply don’t have the money to implement it. “While $100 billion was to be jointly raised in favour of least developed countries each year from 2020, this objective will not be reached before 2023,” Picourt points out. “
With sea levels predicted to increase more in the next thirty years than they have in the previous century, it is vital that finance is accessible to all countries, so that adaptation can take place.