Skip to main content

News

'Time is running out to prepare coastal cities for impact of rising sea levels'



News Thumbnail

Coastal cities could see rises of more than two metres if global warming exceeds 2°C goal

Researchers say urgent action needs to be taken to protect shoreline cities and world heritage sites from coastal flooding, after a new study showed that sea level could be significantly higher than previously thought if global warming exceeds 2°C.

The study, by researchers including Dr Luke Jackson at the Institute for New Economic Thinking at the Oxford Martin School is published today in PNAS, and shows that warming of 2°C, which would occur by 2040 under a business-as-usual scenario, will lead to a global average sea-level rise of 20cm.  Crucially, however, more than 90% of coastal areas will experience greater rises, and the Atlantic coast of North America double that.

Under this ‘business-as-usual’ scenario, where mitigation efforts are unsuccessful, Earth’s global surface temperature would rise by 2°C compared to pre-industrial levels around 2040, and by 5°C around 2100.

With colleagues at the National Oceanography Centre, Delft University of Technology, the University of Copenhagen, Beijing Normal University and the University of Lapland, Dr Jackson projected that, for this scenario, the rate of global sea level rise around 2040 will be about 6mm per year, a rate twice as large as present-day observations. By 2100, this rate would be around 14mm per year, where global average sea level is expected to have risen by around 90cm. This means that a global rise of 60-70cm would occur in about 60 years from 2040 to 2100, compared with 20 cm between now and 2040. It is the increasing speed of sea-level rise over the century that will reduce the time available for adaptation in low-lying coastal regions.

However, by assuming a worst case situation of this scenario, where exceptional amounts of melt-water come from Antarctica and Greenland, projections for 2100 show that global average sea-level rise would be 180cm, 60cm greater than previous estimates. In this case, rises of over two metres are projected for small-island nations such as Micronesia and the Indian Ocean’s Chagos Islands, and coastal cities along the US Eastern seaboard.

Estimates for sea level rises for coastal cities under a 5°C warming scenario include:

Bangkok – lowest projection 49cm, highest projection 191cm

Guangzhou – lowest projection 51cm, highest projection 193cm

Hamburg – lowest projection 56cm, highest projection 195cm

Jakarta - lowest projection 49cm, highest projection 180cm

Lagos - lowest projection 52cm, highest projection 192cm

London - lowest projection 38cm, highest projection 182cm

New York - lowest projection 64cm, highest projection 224cm

Manila – lowest projection 51cm, highest projection 199cm

Whilst sea-level rise increases the risk of coastal flooding, two other factors will also increase risk. First, the rise in population numbers living in coastal megacities (400 million by 2030 including 370 million in Asia, Africa and South America) and second, the effect of local land-subsidence due to the extraction of ground water and river delta sedimentation.

Many cities are building on land left previously unoccupied because of flood risk and with the added effect of subsidence the above projections worsen considerably, with Jakarta projected to see a rise of 3m by 2100. The researchers say that without restrictions on groundwater extraction and the development of alternative water supplies, parts of Jakarta, Ho Chi Minh City, Bangkok and numerous other cities will sink below sea level.

Dr Jackson said: “Multiple factors contribute to rising sea-levels: the warming of the ocean, altered ocean currents such as the Gulf Stream, increased melting of glaciers and ice-sheets, land-water use by ground water extraction and damming, and land-motion, which can be both natural and man-made, for example the subsidence of mega-cities.

“While there are uncertainties about how much sea-level will rise, policy makers must confront two questions. Firstly, what steps need to be taken for coastal regions to adapt to the end-of-century projections? Secondly and perhaps more pertinent is, how will coastal regions adapt to the speed at which sea-level could rise after mid-century? Time is of the essence for rapidly growing coastal cities, coastal heritage sites, and vulnerable tropical ecosystems to adapt to sea-level rise, and it is time that is slipping from our grasp.”

-ENDS-

 

For interviews and further information, please contact:

Sally-Anne Stewart, Communications and Media Officer, Oxford Martin School

+44 1865 287439

+44 7972 284146

sally-anne.stewart@oxfordmartin.ox.ac.uk

 

Caroline Corke, Communications Assistant, Oxford Martin School

+44 1865 616593

+44 7785 927356

caroline.corke@oxfordmartin.ox.ac.uk

 

NOTES

Luke Jackson is a James Martin Fellow of The Institute for New Economic Thinking at the Oxford Martin School directed by Professor Sir David Hendry. Dr Jackson carried out this research at the National Oceanography Centre under the RISES-AM- EU Research project (http://www.risesam.eu/) and subsequently as part of Climate Econometrics (http://www.climateeconometrics.org/) – An Oxford University project in collaboration with the Environmental Defense Fund.

The full paper, Coastal sea level rise with warming above 2 °C (S. Jevrejeva, L. P. Jackson, R.E.M. Riva, A. Grinsted, and J. C. Moore.  PNAS (2016)) can be accessed via EurekAlert at https://www.eurekalert.org/jrnls/pnas/16-05312.htm  To register with EurekAlert visit http://www.eurekalert.org/register.php and request access to PNAS materials.

The Oxford Martin School is a world-leading centre of pioneering research, debate and policy for a sustainable and inclusive future. It supports teams that cut across disciplines because this century’s challenges cannot be understood and addressed by any one academic field alone. The School invests in research that conventional funding channels can’t or won’t take on but which could have a major impact on the wellbeing of this and future generations.

The School seeks to have an impact through new approaches to big challenges, scientific discovery, technological innovation and evidence-based policy recommendations. It also aims to increase public understanding of the most pressing challenges of our time.

Find out more at: www.oxfordmartin.ox.ac.uk on Twitter @oxmartinschool and on Facebook at: www.facebook.com/oxfordmartinschool