- > In this first “World Ocean Review”, we present a report on the state of the oceans which will be followed by periodic updates in the future. Our aim is to reveal the consequences of intense human intervention for the ocean realm, including the impacts of climate change. We already understand some of the effects, but many unanswered questions remain. What is certain, however, is that human society must change its behaviour with the goal of achieving sustainable interaction with the environment and the oceans in particular.
Living with the oceans.
Worldwide, the winter of 2010 was the warmest in the past 131 years. Global climate change has caused a gradual rise in the Earth’s average temperatures. In the coming years the rate of glacial melting will probably accelerate. Sea-level rise will become more rapid. Present calculations indicate that there will probably be a rise of at least 80 centimetres within this century, with as much as 180 centimetres being predicted for the worst-case scenario.
The immense water masses of the ocean act as a buffer, storing considerable amounts of carbon dioxide and heat from the atmosphere. Climatic changes therefore only gradually become noticeable. Scientists anticipate that if greenhouse gas emissions continue unchecked, the sea level could rise by as much as 5 metres by the year 2300. Most of the “mega-cities”, with populations greater than 10 million, are located on or near the coasts. It would require enormous sums of money to protect them, and presumably many of them will have to be abandoned. The ocean may be buffering the most severe consequences of climate change for now. But in the long run we can only hope to avoid these if we strictly curb greenhouse gas emissions today. Experts are concerned that hundreds of thousands of tonnes of methane hydrate could break down due to the warming of seawater – gas masses that are lying inertly in solid, frozen form in the sea floor sediments today. A portion of the methane, which is a powerful greenhouse gas, could then rise into the atmosphere and further accelerate the process of climate change – a vicious circle.
- The oceans absorb many millions of tonnes of carbon dioxide annually. They are the largest “sink” for anthropogenic CO2 emissions. The excess carbon dioxide, however, upsets the chemical equilibrium of the ocean. It leads to acidification of the oceans, the consequences of which are unpredictable. Acidic water disrupts the sense of smell in fish larvae, carbonate formation by snails, and the growth rates of starfish. The phytoplankton, tiny algae in the ocean and vital nutrient basis for higher organisms, are also affected by acidification.
The coastal environment is still being damaged by effluent and toxic discharges, and especially by nutrients conveyed to the ocean by rivers. Thousands of tonnes of nitrogen and phosphorus compounds flow into the ocean around the world, causing an explosion in algal reproduction. In many coastal regions the catastrophe begins with the death of the algae. Bacteria feed on the algal remains and consume oxygen in the water. In these oxygen-depleted zones all higher life forms die off. Efforts to reduce nutrient levels have been successful in Western Europe. Worldwide, however, the input of nutrients is becoming increasingly problematical. People are, without a doubt, abusing the oceans in many respects, and this is increasing the stress on marine organisms. Through over-fertilization and acidification of the water, rapid changes in water temperature or salinity, biological diversity in the ocean could drop worldwide at increasing rates. With the combination of all these factors, the disruption of habitats is so severe that species will continue to disappear.
- It is still uncertain what consequences will ensue from the gradual poisoning of the marine environment with pollutants such as polyfluorinated compounds, which have been used for years as components in non-stick surfaces for pans and in outdoor jackets. These substances become concentrated in the nutrient chain and have recently been detected in the tissue of polar bears. Clearly the oceans continue to be the “last stop” for the dregs of our civilization, not only for the persistent chemicals, but also our everyday garbage. Six million tonnes of rubbish end up in the ocean worldwide every year. The trash is a fatal trap for dolphins, turtles and birds. Plastic is especially long-lived and, driven by ocean currents, it collects in the central oceans in gyres of garbage covering hundreds of square kilometres. A new problem has been identified in the microscopically small breakdown products of plastics, which are concentrated in the bodies of marine organisms.
In the medium term, however, there is a positive trend with regard to ocean pollution. The number of oil spills has decreased. Spectacular tanker accidents now only contribute around 10 per cent of the oil contamination in the oceans. Less conspicuous oil pollution, on the other hand, continues to be a problem. Around 35 per cent of the worldwide oil pollution originates from everyday shipping operations. This source is much more difficult to deal with. As was demonstrated by the explosion of the “Deepwater Horizon” drilling rig, new problems may arise with the trend towards producing oil and gas from wells from greater water depths. >