POSTSCRIPT

SEA-LEVEL RISE: JUST HOW MUCH?

The World Maritime Organization calculates the scale of sea-level rise under different global warming scenarios. The findings are not to be taken lightly.

Global sea level rise is on the march and is definitely a factor to keep an eye on.

A new report, Global Sea-Level Rise & Implications, from the World Meteorological Organization (WMO), highlights the serious consequences of sustained sea level rise in conjunction with a variety of scenarios featuring different levels of sea-level increase.

“Over the next 2000 years,” says the WMO, “global mean sea-level will rise by about 2 to 3m if warming is limited to 1.5°C, to 6m if limited to 2°C and 19 to 22m with 5°C of warming, and it will continue to rise over subsequent millennia.”

Clearly, whatever scenario plays out it will have implications for port planners and not least those in low-lying small islands and port-city locations possessing large populations such as Shanghai, Bangkok, Jakarta, Mumbai, Maputo, Lagos, London, Copenhagen, New York, Los Angeles and Buenos Aires. All these locations and more are under threat from an economic and humanitarian standpoint. Furthermore, the impacts of average sea-level rise are boosted by storm surges and tidal variations, as was made manifestly clear during the landfall of Hurricane Sandy in New York and Cyclone Idai in Mozambique.

Hurricane Sandy inflicted an estimated US$19 billion in damages and lost economic activity across New York City as well as being responsible for a serious loss of life. Cyclone Idai hit landfall in Beira, Mozambique, in 2019, killing over 1000 people across Mozambique, Malawi and Zimbabwe and leaving 2.6 million people in desperate need of humanitarian assistance.

Yesterday To Today

Global mean sea-level increased by 0.20m between 1901 and 2018. The average rate of sea level rise was 1.3 mm/yr between 1901 and 1971, increasing to 1.9 mm yr between 1971 and 2006, and increasing to 3.7 mm/yr between 2006 and 2018. WMO further estimates that during the period 2013-22 that sea level rise has accounted for 4.5 mm/yr. Human influence is cited as the dominant factor behind these increases, at least since 1971.

Global mean sea-level has risen faster since 1900 than in any preceding century, in at least the last 3000 years. Equally striking, the global ocean has warmed faster over the past century than since the end of the last deglacial transition (around 11,000 years ago).

Looking to the future, without concerted action to bring down global warming then, as WMO underlines: “The likelihood and impacts of abrupt and/or irreversible changes increase with further global warming. At sustained warming levels between 2-3 C, the Greenland and West Antarctic ice sheets will be almost completely and irreversibly lost over multiple millenia causing potentially multi-meter sea-level rises. The mass loss is higher with higher warming rates.” And adds: “In the case of very high greenhouse gas emissions (total failure of mitigation) there is a risk of sea-level rise of two metres by 2100 and of up to 15m by 2300.”

The WMO further calculates that: “By 2100 the value of global assets within the future 1-in-100 year coastal floodplains is projected to be between US$7.9 and US$12.7 trillion (2011 value) rising to between US$8.8 and US$14.2 trillion (failure of mitigation).

Responding To The Challenges

The WMO cites the core difficulty in responding to the threat of sea-level rise as – dealing with slow onset changes and changes which as of today are subject to a significant degree of estimation. In a nutshell, if the problem is not knocking on your door then it is difficult to build a sense of urgency to deal with it. The reality is nevertheless present that for the foreseeable future sustained rises in sea level will occur with the probability of increased extreme sea level events. Accordingly, the WMO emphasises that recognising the challenges and planning ahead, in a coordinated manner, is integral to developing an effective response. As it puts it:

“Sea-level rise poses a distinctive and severe adaptation challenge as it implies dealing with slow onset changes and increased frequency and magnitude of extreme sea-level events which will escalate in the coming decades.”