Human activities have dominated the variations in sea level
6.10.2009 8:30
New research shows that human activities have dominated the variations in sea level since 1850. Results come from international research collaboration between researchers from Finland, China, England and Denmark.
Sea level rise is one of the most direct impacts of climate change. Recent predictions suggest rises of 1-2 m before 2100, affecting hundreds of millions of people globally. The causes of sea level variability are essentially driven by changes in global temperature, with a century-scale time delay because it takes time for the oceans to warm and ice to melt or glaciers grow.
- The changes in temperature are driven by both natural variability - changes in solar radiation reaching the Earth and volcanic eruptions, which cool the Earth by blocking incoming sunlight; and man-made causes such as greenhouse gases (warming the planet) and aerosols from pollution, which cause cooling, says research professor John Moore.
- There has been some controversy in deciding the relative amount of natural variability in the Earth’s temperature compared with the man-made forcing. So instead of estimating global temperature, we looked directly at global sea level and the individual driving force components over the last 1000 years, Moore adds.
We find that until 1800 the main drivers of sea level change are volcanic and solar forcings. However, for the past 200 years sea level rise is mostly associated with anthropogenic factors.
- Only 4 cm (25% of total sea level rise) during the 20th century is attributed to natural forcings, the remaining 14 cm are due to a rapid increase in CO2 and other greenhouse gases. This is much larger than the impact of the volcanic eruptions which have produced a net lowering of about 7cm compared with levels expected if there had been no eruptions in the 20th century. It is possible that the man was already affecting sea level well before the large emissions of industrial greenhouse house gases by the change in land use and farming practices around the world, says Moore.
The research was done by an international collaboration between researchers from Finland, China, England and Denmark and the results are published in the scientific journal Geophysical Research Letters.
The blue curve shows the sea level history for the last 1000 years when driven by both natural and man-made forcing factors, the pink curve shows the sea level resulting from only natural forcing. The inset shows the more recent period with the black curve being the observed global sea level variability measured by tide gauge stations.
Link:
The paper will be available at this link shortly http://www.agu.org/journals/pip/gl/2009GL040216-pip.pdf
Contact:
John Moore, research professor, Arctic Centre, University of Lapland, Rovaniemi, Finland, Thule Institute, University of Oulu, Finland & Chief Scientist, College of Global Change and Earth System Science, Beijing Normal University, Beijing, China. +86-13521460942 john.moore.bnu@gmail.com, http://kaares.ulapland.fi/home/hkunta/jmoore/johnpage.htm
Svetlana Jevrejeva, oceanographer, Proudman Oceanographic Laboratory, Liverpool, UK, , Tel: +44 (0) 151 795 4800 (switchboard),
http://www.pol.ac.uk/home/staff/?user=JevreSvet
Aslak Grinsted, geophysicist, PhD. Centre for Ice and Climate, Niels Bohr Institute at the University of Copenhagen, +45 3138-0716, www.glaciology.net
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