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1 Living with the oceans. – A report on the state of the world's oceans

Climate system

The world oceans, global climate drivers
> The oceans cover around 70 per cent of the Earth’s surface. They thus play an important role in the Earth’s climate and in global warming. One important function of the oceans is to transport heat from the tropics to higher latitudes. They respond very slowly to changes in the atmosphere. Beside heat, they take up large amounts of the carbon dioxide emitted by humankind.

Earth’s climate system – a complex framework

> The Earth’s climate is influenced by many factors, including solar radiation, wind, and ocean currents. Researchers try to integrate all of these influencing variables into their models. Many of the processes involved are now well understood. But interaction among the various factors is very complex and numerous questions remain unresolved.

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The great ocean currents – the climate engine

> Ocean currents transport enormous amounts of heat around the world. This makes them one of the most important driving forces of climate. Because they respond extremely slowly to changes, the effects of global warming will gradually become noticeable but over a period of centuries. Climate changes associated with wind and sea ice could become recognizable more quickly.

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Time to act

Climate change will affect the oceans in many ways, and these will not be limited to just altering the currents or heat budget. Increasing carbon dioxide concentrations in the atmosphere are accompanied by higher concentrations in the oceans. This leads to increased carbonic acid levels, which acidifies the water. At present the consequences for marine animals cannot be predicted.
Similarly, very little is known about how the weakening of thermohaline circulation or the Gulf Stream will affect biological communities, such as crab or fish larvae which are normally transported by currents through the oceans. The dangers associated with rising sea level were again stressed during the climate conference in Copenhagen in 2009. Specialists today largely agree that sea level will rise by around one metre by the end of this century if the worldwide emission of greenhouse gases by humans continues to increase as rapidly as it has in recent decades. This will be fatal for island nations like the Maldives, which inundation could render uninhabitable within a few decades. The fact that scientists cannot yet predict with complete certainty what the future effects of climate change will be is not a valid argument for inaction. The danger is real. Human society needs to do everything in its power to bring the climate-change experiment to an end as soon as possible. The climate system reacts slowly to changes caused by human intervention, so there is a strong possibility that some changes are already irreversible. This risk should provide sufficient motivation for forward-looking action to significantly reduce the emission of climate-relevant gases. There is no time to lose in implementing climate protection measures. There are many indications that the most severe consequences of climate change can still be avoided if investment is made today in low-carbon technology. It is time to act.