Global Climate Change and Rise in Sea Level

It is a well-known fact that the climate today is very different to what it was like in yesteryear. The sea level is rising by an average of around 3 millimeters each year, and although this might seem very little, it is not to be scoffed at. This seemingly unimportant rise in sea level threatens low-lying areas, and dramatically increases erosion processes on beaches and coastal zones in general.

Tide gauges have been used to determine sea level for hundreds of years, but today the most complete global measurements now come from space. Tide gauges are not sensitive enough to detect changes in the rate of sea level rise and therefore are not very useful in monitoring climate change. Tide gauges also work in a very localised manner, only taking measurements of their immediate surroundings. In contrast, the Topex/Poseidon satellite observes the entire ocean and has been making precise measurements of global sea level since it was launched in 1992. Its successor, Jason, is now continuing the same ocean observations.

According to Dr. Steve Nerem, a member of the Topex/Poseidon and Jason1 science team, the annual global increase in sea level is 2.8mm. In some areas this is actually much higher, around 5mm. Considering that more than 2 billion people live within 100km of the coast, these values are worrying. Of even more concern is the fact that the scientists themselves still haven’t agreed on the cause for sea level rise. Nerem says it could be part of a long climate pattern, but the accepted cause is global warming. Sea level is understood to be a barometer of climate change, and the rises in sea level seem to be consistent with climate change models. 

The phenomenon however is not new; it actually began in the middle of 19th century. What’s worrying the scientists is that the evidence points to the current rate being considerably faster than it has been for the past several thousand years.

Sea level is determined by temp-erature and ocean mass. Sea level therefore rises because of warm water ex-panding and because of water being added to the ocean as glaciers and ice sheets melt. Scientists think that thermal expansion accounts for 0.5mm of the sea level rise per year. This translates to 5cm per 100 years. Global sea level is rising by more than 20cm per 100 years, and scientists think that the remaining 15cm are mainly due to mountain glaciers (4cm) and the great ice sheets of Antarctica and Greenland (11cm).

NASA's new Grace mission will be able to calculate the ocean's mass, helping pinpoint whether rising sea level is a result of more water in the ocean or expansion due to warming waters. A new generation of tide gauges and monitoring devices provide details on sea level changes in specific locations.

Text Box: Sea level rise in mm for the Mediterranean Region from the year 1993 to 2000. Note that the Eastern Mediterranean has experienced a rise of more than 10mm.

Meanwhile, Jason continues the global sea level measurements begun by Topex/Poseidon more than 11 years ago, building up a record of sea level change that may help explain the past and predict the future. Ironically, Topex/Poseidon was never expected to be able to make precise enough measurements to monitor something as small as millimeter changes in global sea level. Jason 1 may improve on these measurements even more.

The Maltese Islands contribute to the global activities concerning monitoring of climate change. Atmospheric measurements made by the national Meteorological Office (Malta International Airport) and the University of Malta (Physical Oceanography Unit and the Institute of Energy Technology), already furnish the basis of a network of meteorological stations to observe key parameters in the Maltese Islands. The Meteorological Office and the Water Services Corporation maintain a rain gauge network. Given the core business and support-infrastructure of these two entities the gauges are located such that one is predominantly sampling precipitation in urban areas whilst the other is targeting more the rural areas. Together both networks provide an ample coverage of the Maltese islands.

The Physical Oceanography Unit at the University of Malta undertakes measurements in real time of sea level and temperature in Portomaso and in delayed mode in Mellieha Bay. It also undertakes fundamental research in coastal meteorology, hydrography and physical oceanography with a main emphasis on the experimental study of the hydrodynamics of the sea in the vicinity of the Maltese Islands. It offers facilities for the gathering, processing, analysis and management of high quality physical oceanographic observations both for long term and baseline studies as well as for general applications in marine environmental research and assessments. The Department of Biology and the environment section within the Malta Environment and Planning Authority are the main local entities that assess sea-water quality.

The future of climate change, and therefore sea level rise, depends on the action of each citizen and on a commitment to a more responsible and environmental friendly attitude. Achieving such a level of commitment at a national level is by no means easy. It requires a superior public responsibility towards the environment, building on a substantial and sustained investment in comprehensive education on environmental issues and targeting all groups of the local population including children at all levels of the educational system and also the layman.

Educational programmes should be designed to improve environmental literacy, to empower citizens with knowledge about the implications of everyday practices on emissions and the effects on climate change, and to promote a positive attitude towards ‘green’ practices even if these involve a cost and/or require a change in lifestyle.