Monday, October 3, 2011

Sea Level Rise and Australia


Average global sea level is rising at the fastest rate in 2000 years according to scientists, and north and western Australia is copping more than double the global average in sea level rise. The rate of increase has accelerated in the last 20 years which has been attributed by scientists to thermal expansion, small glacier melt and accelerating ice sheet loss from the Greenland and West Antarctic ice caps caused by climate change and global warming. A peer reviewed scientific study published in June 2011 from the Potsdam Institute for Climate Impact Research has shown the rate of Sea level rise is connected to global temperature rise.

According to the CSIRO (PDF) "From 1870 to 2007, the global average sea level rose by close to 200mm. Sea levels rose at an average of 1.7mm per year during the 20th century and about 3.0mm per year from 1993-2009. These levels are global averages and because of the differing movements of ocean currents around the globe, results vary from place to place. This is true for Australia where since 1993 levels have risen 7-10mm per year in the north and west, and 1.5-3mm in the south and east."


Sea level changes are measured through satellite altimetry and by in situ gauges and instruments. In situ baseline stations also help in calibrating satellite measurements. The technology has come a long way from basic tidal gauges: base stations now use SEA-level Fine Resolution Acoustic Measuring Equipment (SEAFRAME) which involves two independent means of measuring sea level. The baseline sealevel monitoring network includes 14 stations around Australia. The data is also contributed to the University of Hawaii Sea Level Centre, Permanent Service for Mean Sea Level, Global Sea Level Observing System (GLOSS) under the auspices of the World Meteorological Organisation (WMO) and Intergovernmental Oceanographic Commission (IOC).

Sea levels change all the time with weather, climate, ocean currents and geological isostatic adjustment caused by melting of ice sheets and redistribution of their mass to the oceans. There are seasonal, interannual and interdecadal fluctuations, as well as fluctuations associated with events such as the El Niño Southern Oscillation (ENSO) cyclic weather pattern.

The recent strong La Niña pattern during late 2010 and into 2011 resulted in 10-20cm extra sea level anomaly at most sites across the northern and western half of the Australian mainland and as much as 25cm at Hillarys near Perth. "The positive sea level anomalies at Hillarys, Rosslyn Bay and Cape Ferguson during the 2010/11 La Niña were the highest since the stations were installed in the early 1990’s and were a major reason why record-high monthly mean sea levels were observed at these stations." said the 2011 sea level report (PDF) from the National Tidal Centre, Australian Bureau of Meteorology.

The most serious impacts of sea levels will be caused by extreme events such as tsunamis and storm surges from tropical cyclones. In a warmer world the frequency and intensity of tropical cyclones and hurricanes will be increased thus contributing to greater storm surge capacity. (See 2005 report in Science: Changes in Tropical Cyclone Number, Duration, and Intensity in a Warming Environment)

The SEAFRAME stations detect tsunamis such as the magnitude 9 earthquate that struck Japan on 11 March 2011 producing a wave that was detected around Australia: Cape Ferguson (0.2m from trough to crest), Rosslyn Bay (0.4m), Port Kembla (0.6m), Spring Bay (0.6m), Burnie (0.2m) and Portland (0.2m). Evidence of the tsunami was also detected at Stony Point and Lorne SEAFRAME stations. Similarly cyclones produce storm surges which are measured. At Cape Ferguson the storm surge of Tropical Cyclone Yasi was measured at 2.0m on 2 February 2011.

Climate change is causing average global sea levels to rise due to a number of processes:

The transfer of mass as ice sheets to water in the ocean will result in variable rises in sea level for different regions due to the change in gravity. Change in Sea level around Greenland and northern continents may remain minimal or actually fall in certain areas, where as equatorial regions and the southern hemisphere may experience rises much greater than the average. Hans Joachim Schellnhuber, the director of the Potsdam Institute for climate impact research called this the injustice of sea level rise - where countries that have least contributed to the accumulated greenhouse gases which cause climate change and sea level rise will be most impacted.

Recent Sea Level around Australia

Recent Sea Level trend based upon National Tidal Centre, Australian Bureau of Meteorology Seaframe data gauges installed 1990-1993 and measured to June 2011; and net sea level trend after vertical movements in the observing platform relative to a local land benchmark and the inverted barometric pressure effect are taken into account.

  • Cocos Islands - 8.1mm/year - Net sea level trend: 3.4mm/year
  • Groote Eylandt (NT) - 9.0mm/year - Net sea level trend: 8.9mm/year
  • Darwin (NT) - 8.6mm/year - Net sea level trend: 8.3mm/year
  • Broome (WA) - 9.1mm/year - Net sea level trend: 8.4mm/year
  • Hillarys (near Perth WA) - 9.1mm/year - Net sea level trend: 9.0mm/year
  • Esperance (WA)- 6.0mm/year - Net sea level trend: 5.5mm/year
  • Thevenard (SA) - 4.5mm/year - Net sea level trend: 4.3mm/year
  • Port Stanvac (near Adelaide SA) - 4.7mm/year - Net sea level trend: 4.3mm/year
  • Portland (Vic) - 3.2mm/year - Net sea level trend: 3.1mm/year
  • Lorne (Vic) - 2.7mm/year - Net sea level trend: 2.8mm/year
  • Stony Point (Vic) - 2.6mm/year - Net sea level trend: 2.6mm/year
  • Burnie (Tas) - 3.1mm/year - Net sea level trend: 2.9mm/year
  • Spring Bay (Tas) - 3.5mm/year - Net sea level trend: 3.7mm/year
  • Port Kembla (NSW) - 3.2mm/year - Net sea level trend: 2.6mm/year
  • Rosslyn Bay (Qld) - 3.8mm/year - Net sea level trend: 3.5mm/year
  • Cape Ferguson (Qld) - 4.8mm/year - Net sea level trend: 4.7mm/year

Source: National Tidal Centre, Australian Bureau of Meteorology June 2011 report (PDF)

Projections of sea level rise

The IPCC 4th report in 2007 estimated sea level rise projections of 18 to 59cm by 2100, but with a caveat that not enough was known of the dynamic processes in ice sheet melting and it's contribution to sea levels. Much research into Ice sheet melting and disintegration has ocurred since this report. A 2009 study by the Potsdam Institute for Climate Research Proceedings of the National Academy of Sciences of the United States of America warned that sea level could rise much faster than previously expected. By the year 2100, global sea level could rise between 75 and 190 centimetres.

Dr John Church, a specialist researcher in climate and sea level change from the CSIRO warned at an international scientific conference in Copenhagen prior to COP 15 that "Sea level is currently rising at a rate that is above any of the model projections of 18 to 59 cm". he said. "Our study centered on Australia showed that coastal flooding events that today we expect only once every hundred years will happen several times a year by 2100", said John Church.

A study published in June 2011 in the journal Proceedings of the National Academy of Sciences (PNAS), found that the Fastest Sea-Level Rise in 2,000 Years is Linked to Increasing Global Temperatures. The rate of sea level rise along the U.S. Atlantic coast is greater now than at any time in the past 2,000 years according to the study, and has shown a consistent link between changes in global mean surface temperature and sea level. The California coast has experienced sea level rise of nearly eight inches according to a 2009 study - The impacts of sea-level rise on the California Coast. Under medium to medium‐high emissions scenarios, mean sea level along the California coast is projected to rise from 1.0 to 1.4 meters (m) by the year 2100.

The risks of sea level rise have been outlined in a book by Dr Peter Ward, a paleontologist and professor of Biology and of Earth and Space Sciences at the University of Washington, Seattle. The book, The Flooded Earth: Our Future In a World Without Ice Caps, warns that the single biggest threat and impact of climate change will be rising seas, rather than hot weather, or even drought. Ward explains why, how, and how fast the seas will rise, due to global warming.

Projected Impacts of Sea Level Rise in Autralia

Rising sea levels will have devestating consequences around Australia including:

  • Gippsland - "There are serious consequences of rising sea levels for the Gippsland region. The Gippsland Lakes, including Ninety Mile Beach and Corner Inlet, represent one of the most vulnerable coastal areas in Australia. Within 50 years, parts of the Gippsland coast will be inundated to an extent requiring protection or relocation of houses and buildings." (Climate Commission - Climate Change Impacts for Gippsland)
  • Illawarra / South Coast NSW - "Rising sea levels will exacerbate existing vulnerability of coastal towns and infrastructure in the Illawarra/ NSW south coast region." (Climate Commission - Climate Change Impacts for Illawarra NSW South Coast)
  • West Australia - "Sea levels along the west coast of Australia have been rising at more than double the global average. With significant part of the population living in coastal cities and towns, rising sea levels pose significant risks to Western Australia’s coastal infrastructure and iconic sandy beaches." (Climate Commission - Climate Change Impacts for Western Australia)
  • South Australia - "Rising sea levels will exacerbate existing vulnerability in South Australia’s coastal towns and infrastructure." (Climate Commission - Climate Change Impacts for South Australia)
  • A 2009 report by the Australian Government - Climate Change Risks to Australia's Coasts povides a risk assessment of climate change and rising sea level to Austrlian coastal communities. The report shows between 157,000 to 247,600 existing residential buildings will be at risk from sea inundation by 2100, under a sea-level rise scenario of 1.1 metres.
  • James Hansen, NASA climatologist, in a 2007 interview on the 7.30 report, predicted the likelihood that the earth will pass a tipping point resulting in Sea Level Rise of up to a metre every 20 years. The trigger for this is an extra degree of global warming resulting in the runaway melting of the Greenland and West Antarctic Ice sheets.
  • A 2006 Insurance industry study in Australia has identified 700,000 buildings at risk nationwide from rising sea levels caused by human induced climate change.

Sources

  • Australian Bureau of Meteorology Yearly Data Reports - Australian Baseline Sea Level Monitoring Project.
  • For rise in global average sea level from satellite altimeter data for 1993–2009 and from coastal and island sea-level measurements from 1880 to 2009 please refer to:
    'Sea-Level Rise from the Late 19th to the Early 21st Century' by John A. Church and Neil J. White, Surveys in Geophysics, Volume 32, Numbers 4-5, 585-602, DOI: 10.1007/s10712-011-9119-1. The global average after correcting for glacial isostatic adjustment, the estimated rate of rise is 3.2 ± 0.4 mm year from the satellite data and 2.8 ± 0.8 mm year from the in situ data.
  • Read more on sea level rise measurements and projections particularly as they relate to Australia at the CSIRO and ACECRC Sea Level Rise website.