The ABCs of Sea Level Rise

• Melting ice and permafrost due to global warming are increasing ocean mass and volume, accounting for half of the current sea-level rise.

• The other half of sea-level rise comes from thermal expansion as warmer water occupies more volume.

• Sea level rise varies between regions. Climate risk data can help financial institutions understand the physical risks their assets face.

As the world’s air temperature rises due to climate change, snow, ice, and permafrost are melting. This water runs off into the oceans, adding mass and volume.

The oceans’ increased mass does not really push the ocean floor downwards, nor push aside the continents. The main way to account for the increased volume is to go up, witnessed as sea-level rise, with this melt accounting for around half of sea-level rise seen at the moment.

The other half of today’s sea-level rise is from ‘thermal expansion’.

Water’s density changes with temperature. As the oceans absorb heat from the atmosphere, the water’s temperature rises, its density decreases, and so its volume increases. We witness this volume increase as sea-level rise which compounds coastal flooding.

Sea-level rise has averaged about 1.3 millimetres per year from 1901-1971, accelerating to close to 4.0 millimetres per year over the past decade. This rate continues to accelerate. Without any changes to our actions causing climate change, by 2100 sea level could rise to over 1.0 metre above the 1980’s level, at the high end.

One complication in all these calculations is that sea level is not the same everywhere all the time. The average level - not considering waves, tides, or wind effects - varies by tens of centimetres globally. Also, ocean mixing is incomplete leading to large regional variations in sea level.

Tens of centimetres of variation is small compared to potential maximum sea-level rise. If the huge ice sheets covering Kalaallit Nunaat (Greenland) and Antarctica melt significantly, then they could add more than a dozen metres to sea level — higher than a four-storey building — over coming centuries. If all this ice melts, then sea level would reach the top of high-rise buildings.

Ultimately, any coastal location without steep topography could be inundated by sea-level rise. Even with steep topography, assets atop cliffs can disappear into the sea if erosion is augmented by higher sea levels and accompanying storms. Bluffs, dunes, and steep slopes can be swiftly eroded by rough seas and waves.

Large concentrations of assets are built on or beside beaches or similarly low-lying coasts around the world.

For the US coastline, major cities from New York down to Miami and then along the Gulf Coast from Tampa to New Orleans and Houston display large physical risks to sea-level rise. Other major cities with significant swathes of assets at or near current sea level include Amsterdam, Hamburg, Ho Chi Minh City, Jakarta, Lagos, London, Manila, Rotterdam, Shanghai, and Singapore. C

oastal flooding already poses major physical risks in these locations with long-term planning generally being about barriers, barrages, and structural walls rather than considering the possible need to move assets or to divest in them.

Asset managers need to consider their assets now given the ongoing and accelerating sea-level rise.

For the maximum possible sea-level rise, due to ice sheets melting entirely, they have centuries to prepare for the full impacts which would reconfigure the world’s shores and require major ports to be rebuilt.

Most coastlines with cities offer a long history of data covering approximate shoreline changes alongside previous coastal flooding and storms, the physical risks, and the consequences.

Human engineering has permitted so many assets to be sited at or near sea level, from the barrier islands comprising Miami Beach with its elegant hotels and apartments through to the high rises of the financial centres of Wall Street in New York, Canary Wharf in London, and the city of Singapore.

Consequently, past data does not always suffice to indicate directly the current or future physical risks from sea-level rise, suggesting the need for climate risk data experts such as Climate X that can extrapolate, model, and estimate for physical risks and potential losses.

Some places such as in southeast England and southern Louisiana are actually removing assets from low-lying coasts in order to permit the sea to encroach, reducing the physical risks further inland.

This decision is termed ‘managed realignment’, as in deliberately realigning the coast to be more in line with what the sea wants. It is often mistermed ‘managed retreat’, since it is not a retreat, but is a strategy to avoid damage and losses to assets by re-siting them in places away from the physical risks from sea-level rise.

Sometimes, as fast as assets are moved, others spring up.

Florida’s new homes at sea level counter Louisiana communities seeking to move. London is building in storm surge floodplains perhaps even faster than nearby coastal areas are being turned into salt marshes. Data on all these locations and their continuing changes helps financial institutions understand the physical risks facing their assets from sea-level rise.

These analyses represent an important step forward in planning for and adapting to the future.

Asset managers who know what sea-level rise is (by using reliable climate risk data), how and why it is happening, and where and why it could be of most concern are opening doors for assessing, managing, and adapting to the physical risks to their assets.