How climate change changes the oceans

The effects of climate change are complex and are only beginning to unfold their potential for wreaking havoc. However, historical data and current predictions are painting a gloomy future: temperature-stress, sea level rising, coastal erosion and acidification are drastically changing the marine ecosystem in many regions.

The life insurance system of the planet is at risk. The ocean and coastal regions are changing more rapidly than it has ever been recorded in history and the cause for this is the climate change, enhanced by humanity. This statement was recently made by the Intergovernmental Panel on Climate Change (IPCC) in its fifth paper, in which the international committee of 800 scientists summarises the current state of affairs regarding global warming and new, worrying predictions for the future.

The last thirty years were the warmest in the last 1.400 years. Whilst global temperatures have risen by 0.14 degrees Celsius in the last decade (with 0.6 degrees since the industrialisation), ocean temperatures have risen by 0.4 degrees between 1970 and 2010. And the end is not yet in sight: A new temperature record for the North Pacific, Mediterranean and parts of the North Atlantic were recorded in 2014. Global warming will, according to the IPCC, rise by another 4 degrees Celsius by the end of this century, if we don’t reduced emissions.

When glaciers sink into the ocean…

The rising temperatures are leading to an explosion of the ocean, as warmer waters have a larger volume, meaning that the sea level is rising continuously. Current estimates state a sea level rise of between 28 and 98 centimetres, with regional differences, and there is no end in sight. Partially this is also made up of land-based input from melting glaciers – 80 percent of land based ice masses are retreating. The Greenland ice sheet loses 100 – 350 billion tons of ice annually. Once all of this ice has melted, the sea level will have risen by 7 metres. In order to stop the complete melting of the ice sheets globally the “2 degrees Celsius goal” was put in place as an upper limit for global warming.

For floating arctic ice global warming also poses a threat. Feedback effects have lead to a reduction in the previously 16.2 million square kilometres ice coverage to 14.5 million in the last 30 years (a difference equal to the size of Iran). The population of polar bears and other species that are reliant on the ice sheets have been decreasing with an alarming speed. Through the rapid melting of ice in spring a high amount of ice bound algae are being released, which then sink in the water column where they feed bacteria, which in turn leads to a reduction in oxygen in the water and the creation of dead zones in the Arctic.

But not only the highly sensitive poles are suffering from global warming. The tropic and sub-tropic regions, too, are suffering, leading to extreme temperature variations, storms and massive downpours. The loss of habitat affects many species, and land-based nutrient input is doing its part to increase the stress on the ecosystem. Even global currents, formed by the salinity and temperature gradient in the ocean, have changed, just as it has in the past.

… and the ocean can barely buffer any longer…

Global warming through greenhouse gasses is mostly driven by the emission of carbon dioxide. Next to all the other gasses, this one is also a vital component for the geochemistry and biology of the ocean. Until now, the ocean has functioned as a sink for carbon dioxide, being able to take up more then 60 times as much carbon dioxide as the atmosphere.

Through the burning of fossil fuels the carbon dioxide concentration in the atmosphere has risen to 395 ppm – the fastest increase in the last 800.000 years. And the carbon dioxide concentration is the ocean is rising, too. Currently the ocean is taking up approximately a quarter of global emissions. However, the ocean is becoming increasingly acidic through this uptake, as it’s uptake leads to the formation of carbonic acid. Extrapolations show that the northern Indian Ocean has become 10 percent more acidic. But colder waters such as the waters off the coast of Siberia and Alaska (the Bering Strait is considered the most acidic ocean), the Antarctic and the northern Pacific, due to the deep water formation and the algal blooms, are more affected by this and are changing rapidly.

The pH value of the ocean has changed 0.1 since the start of the industrialisation – a value shift that is very drastic for many ecological processes. If the pH goes below 7.5 the calcite shells of many organisms will dissolve. The so-called biological carbon dioxide pump for the storage of this gas could thus come to a halt, after having functioned well and efficiently for more than 20 million years. Living in acidified waters first harms deep sea corals and planktonic organisms, but other corals and tropical organisms are not spared. Effects on the coastal protection from stores, tourism and global fisheries are unavoidable.

…risks are being exponentiated

By now the creeping effects of climate change can be witnessed everywhere in the marine ecosystems. On top of this there are further pressures through problems such as overfishing, increasing populations, pollution and the loss of species diversity and richness, to name a few. In the world climate report of the IPCC possible consequences of climate change for global food security are being discussed. Along with wheat, rice and corn, fisheries are most important, as around 500 million people are directly reliant on the ocean for its food provision. Ocean-sourced products provide about a fifth of the global protein.

The experts of the IPCC state that climate change will lead to more productive fisheries in some regions, like the north Atlantic waters for example, due to a reduction in ice masses. In all tropical waters, however, the rising temperatures, acidification and loss of habitat will reduce the productivity of the ecosystems drastically. Africa, East Asia and the Island states will be the first to lose: Through coral bleaching and the rising sea level the coastal regions will suffer drastic economic losses.

Fisheries in the south rely on a healthy ecosystem. However, the productivity, species richness and planktonic dispersion will change in the warming tropical waters. According to the IPCC, landings for thousands of commercially exploited fisheries will be drastically reduced by 2060, in comparison to landings between 2001 and 2010. In the Caribbean the landings will continue to reduce and through the increase of oxygen-depleted zones many species, like the Humboldt squid, will extend their habitats globally. They could then be a competition to industrially exploited species, such as salmon.

Although the consequences of climate change have not yet been noticed strongly in the rich waters off Peru or Namibia, however, these ecosystems, too, are not safe from the damage. With increasing upwelling events the open ocean species could profit from algal bloom events whilst populations closer to the coast would suffer from reduced oxygen concentrations and increased nitrogen input through fertilisers. A lack of upwelling would lead to a decrease in nutrients and biomass in all involved ecosystems. These kinds of “years of famine” can have drastic effects for birds, marine mammals and lastly also for fishermen.

Climate change is showing rapid changes in the marine ecosystems with direct consequences for the food security for society, especially in the southern regions. And in these regions most cannot afford the possible yet expensive adaptation options such as coastal protection, relocation and development of alternative food sources or industries. However, exactly in these regions – for example, through the collapse of fisheries – many people are living on the brink of poverty, making malnutrition a serious threat. As long as there are no sufficient countermeasures this bares serious risks for conflict in the future.

Text: Onno Groß, 2016