Effects of climate change on marine ecosystems

Climate change is the global warming of the atmosphere as a result of increased CO2 levels in the atmosphere (greenhouse effect). Just as threatening as an increase in temperature for the oceans is acidification as a consequence of the direct dissolution of CO2 in surface water. With the CO2 input into the atmosphere, mankind has triggered processes that will probably adversely determine the condition of the oceans for thousands of years. Some of the effects can already be observed today - such as sea level rise, warming of surface waters and acidification of seawater. What is new is the global dimension of the changes, which threaten the oceans and their natural resources as well as the very basis of human life. Among other things, the oceans are a source of food and the coasts are a settlement area for many people.

The rise in temperature, in particular, has already led to shifts in species occurrence and thus to changes in marine ecosystems. Both the stocks themselves and their distribution - of both commercially important and non-commercially exploited fish species - will change in unpredictable ways. Stocks that are already overfished may become more sensitive, and future fisheries management may face even greater difficulties than before. Temporary closures of fisheries for certain target species may eventually be necessary.

It is already foreseeable today that corals and other calcifying organisms will be affected because of acidification and because of the rise in temperature. A complex interplay of human influences - including the increase in carbon dioxide in the atmosphere - threatens coral reefs.

Because the global climate system responds very slowly and sluggishly, sea level rise will be expected even if CO2 emissions are drastically limited immediately. As the frequency and severity of storms increase, the habitats and livelihoods of many coastal dwellers - especially in poorer regions as a result of flooding, storm surges and sea level rise - may be threatened.

A brochure published by the Federal Environment Agency illustrates the consequences of climate change for marine ecosystems.

Combating climate change through marine geoengineering?

Efforts are underway to mitigate anthropogenic global warming through deliberate and targeted interventions in the climate system, usually on a large scale. These measures are referred to as geoengineering or "climate engineering." They carry many risks and their effectiveness has not yet been proven. They can therefore in no way replace the necessary reduction of greenhouse gases.

Since the oceans are the largest and most important carbon sink on our planet, absorbing about 50 times as much carbon as the atmosphere, many geoengineering proposals aim to exploit this carbon sink.

Marine geoengineering methods currently under discussion include, for example, ocean fertilization , ocean liming, and crop waste dumping. Within these methods, ocean fertilization occupies a certain special position, as this method has already been researched in practice and aspects such as effectiveness and risks can already be evaluated.

Ocean fertilization

Algal blooms fix CO2, which would be temporarily removed from the "system" after the bloom dies and sinks to the ocean floor and is (temporarily) stored there. The idea of using iron fertilization in the oceans to halt the rise in CO2 concentrations in the atmosphere is not new.

In the early 1990s, U.S. oceanographer John Martin found that large regions of the world's oceans were almost devoid of unicellular algae (phytoplankton), even though the macronutrient salts nitrogen and phosphate were present in sufficient quantities. It turned out that in these "paradoxical" zones, a micronutrient salt essential for algae, iron, was missing, limiting or eliminating potential blooms of unicellular algae (phytoplankton) in the ocean.

Since this observation, thirteen marine expeditions have been conducted to test the "iron hypothesis" with fertilization experiments. Three of these experiments, Eisenex (2000), EIFEX (2004), and LOHAFEX (2009) were conducted by the Alfred Wegener Institute for Polar and Marine Research (AWI) in cooperation with scientific institutions in other countries. While the ocean fertilization experiments were quite successful in terms of scientific knowledge gained, the enthusiasm based on theoretical studies regarding the potential of CO2 storage dissipated rather quickly.

Effects of ocean fertilization on the ecosystem.

Many of these effects cannot be assessed today because previous experiments have been too small-scale (up to 300 km 2 ) and have not lasted long enough (< 40 days) to detect such effects. However, it is very likely that large-scale intensive ocean fertilization will lead to effects similar to those of eutrophication (over-fertilization), a well-studied phenomenon that occurs in marine waters due to excessive nutrient inputs.For example, accumulation of dead algal biomass causes oxygen deficiency in the water column and on the seafloor, even leading to asphyxiation of organisms. In addition, oxygen deficiency in sediments leads to the production of very potent greenhouse gases such as nitrous oxide and methane, which could outweigh the effect of CO2 reduction on climate and therefore need to be accounted for in the climate balance of ocean fertilization.Experiments have also shown that ocean fertilization can promote toxic algal species that can have undesirable negative effects on marine life such as fish and human health (through consumption of shellfish and fish) through toxin production. Finally, potential effects are also to be expected in ocean areas that are supplied with water masses from the fertilized region via ocean currents, because these water masses have already been deprived of nutrients essential for algae growth ("nutrient robbing").The German Advisory Council on Global Change (WBGU) also clearly distances itself from iron fertilization in its reports of 2006 (special report "Future of the Oceans") and 2003 (main report "Energy Transition towards Sustainability"). The WBGU says: "On the one hand, the expected magnitude of the volume effects is probably rather small [...] and there are doubts about the sufficient long-term nature of storage [...]. For another, the risks of large-scale iron fertilization are difficult to assess with regard to the indirect consequences for marine ecosystems."

Legal requirements

Based on a marine geoengineering activity planned by the private sector, in October 2008 the Parties adopted the politically very significant decision that research activities in the field of marine geoengineering should continue to be permitted, while all other activities, especially those of a commercial nature, are prohibited.

In 2013, the London Protocol Parties adopted by consensus legally binding regulations to control marine geoengineering. These regulations relate primarily to marine fertilization. Analogous to the 2008 decision, commercial activities for fertilizing the oceans are prohibited. In principle, however, corresponding research projects remain permissible. However, these must be examined in advance to determine whether the experiments are scientifically necessary and whether they will have an unacceptable impact on the environment. The new regulations also make it possible to subject further types of marine geoengineering measures to state control in the future, should this prove necessary.

The Assessment Framework for the Review of Research Projects, also adopted in 2013, sets specific requirements for the review addressed above for marine fertilization projects in terms of scientific quality and potential adverse environmental impacts. According to the "Assessment Framework", economic interests must not influence the direction of the research project. Other countries and interested parties must be consulted in advance of research activities.

The new requirements under the London Protocol have not yet entered into force because they have not been ratified by enough states (two thirds of the signatory states). Germany adopted the necessary changes to its national law in the fall of 2018. They will enter into force in June 2019.

Ocean Liming

Ocean liming aims to increase the pH of seawater so that more CO2 can be captured from the air. This can be achieved, for example, by adding calcium oxide. To do this, calcium oxide would first have to be obtained on land by thermal decomposition (heating to 850ºC) of limestone. A process that requires a lot of energy and water and also releases carbon dioxide. Rough estimates show that 1.5 km3 of limestone could fix 1 Gt of CO2 in the ocean. However, it would take 750 years for the current atmospheric CO2 levels to be reduced to natural concentrations, assuming that 1 km3 of limestone is mined per year (Borel 2008). Logistically, ocean liming would represent an enormous expense, since very large quantities of limestone would have to be mined and transported. Proponents of the method argue that liming could also mitigate ocean acidification caused by climate change. However, this is equally questionable, as local liming only raises the pH in a limited area. Furthermore, the extremely alkaline water could even harm marine organisms when introduced. Critics consider the very approach implausible, since the local injection of calcium oxide would make the seawater so basic that precipitation of calcium carbonate would probably occur immediately. Even if this were not the case, scientists argue that the amount of CO2 sequestered in the ocean would not significantly exceed the amount released when the limestone decomposes, and thus the entire process would tend to produce additional CO2.

Lime would therefore have to be introduced into the ocean in substantial quantities to achieve any appreciable increase in the lime content of seawater. However, since the surface water of the oceans is supersaturated with lime, this would not lead to an accelerated dissolution of CO2 in seawater. Undersaturation with lime only occurs at depths of several thousand meters. However, only a small amount of anthropogenic CO2 has arrived there so far. Most of it is still in the upper ocean layers and will only be distributed throughout the entire water column in 1,000-2,000 years. In the long term (in 10,000 years and more), it is precisely this reaction that will bind most of the anthropogenic CO2. The natural calcium content in the oceans is sufficient for this (unless global CO2 production exceeds 5,000 Gt C). In addition, the negative effects of liming on marine ecosystems would have to be considered. The light climate of the oceans would be altered by vast zones of turbidity in which photosynthesizing plants could no longer grow. This would have an impact on food webs, fishery yields and the global CO2 balance, as less phytoplankton would be available and less CO2 could be captured.

Sinking of crop waste

It is proposed to remove up to 30% of crop waste (e.g., straw), from fields, load it onto ships, and dump the bales weighted with stones in places where the ocean is more than 1,000-1,500 m deep. In these large ocean depths, decomposition of the organic material is very slow due to the cold, lack of oxygen, and lack of bacterial enzymes to break down cellulose. Assuming that 92% of the CO2 contained in crop waste is fixed at depth, approximately 15% of the annual global increase in CO2 emissions (0.6-0.9 Gt) could be removed from the atmosphere by this method. However, it would be necessary to ensure that the transport of crop waste does not produce more CO2 than is ultimately fixed in the ocean.

We can only speculate about the ecological impacts of this method because deep-sea processes are largely unexplored, but negative impacts of this method on complex marine ecosystems are very likely, even if harvest wastes are deposited only where terrestrial biomass is already deposited at greater ocean depths by natural processes (e.g., off large estuaries). It remains open whether decomposition processes can lead to the release of harmful substances (putrefactive gases, greenhouse gases) and significantly affect marine organisms in a larger region, with unpredictable consequences also for humans. Should the bales detach from their anchor and float to the surface, decomposition processes will result in the release of the sequestered CO2. On land, the removal of crop waste from the fields would deprive the soil of important nutrients and trace substances.

Statement of the Federal Environment Agency on ocean fertilization

In environmental protection and thus also in marine protection, the Federal Environment Agency generally follows the environmental policy approach that emissions, inputs and losses of substances that are undesirable in the oceans are to be reduced or avoided at the sources.

Policy approaches that provide for additional discharge of substances into the oceans, and whether for "precipitation" of other substances or compounds or for ecological "manipulation," are rejected or viewed very critically because they depart from what we consider to be the primary effort of working on a source-by-source basis and contain many imponderables.

Current research findings cast considerable doubt on whether ocean fertilization is an effective measure to address climate change. Currently, there is no scientifically robust evidence that iron fertilization is capable of reducing atmospheric CO2 levels to a degree that is relevant to climate.

Furthermore, for all methods developed so far, there are considerable doubts about the sufficient long-term storage and the efficiency of the methods. UBA considers incalculable and harmful effects of ocean fertilization to be highly probable, since it interferes with marine food webs, some of which are very complex, and therefore recommends that future experiments investigate the effect of ocean fertilization on deeper water layers, on sediments and bottom-dwelling organisms, and on fisheries. In addition, UBA advocates government control with mandatory approval of research activities on ocean fertilization.

The Federal Environment Agency's position paper entitled "Is ocean fertilization suitable for combating climate change?" contains a detailed overview of the topic of ocean fertilization and a detailed statement.

Federal Environment Agency position on marine geoengineering.

Currently, the marine geoengineering methods outlined above and other geoengineering methods are controversially discussed as options to combat climate change. In the view of the Federal Environment Agency, geoengineering measures do not represent an alternative to mitigation and adaptation measures - the two pillars of classical climate protection - in the foreseeable future.

The application of geoengineering measures could lead to a paradigm shift in three respects, which the Federal Environment Agency rejects in principle. First, to the assumption that humans are capable of understanding and controlling global environmental processes; second, to the assessment that geoengineering could replace mitigation and adaptation measures; and third, to the change of course to jettison fundamental concepts of international environmental law, such as mitigation of pollutant input into the environment at the sources.

Geoengineering measures appear attractive because a technical solution to the climate problem suggests a "business as usual" approach and could render international negotiations and emissions mitigation efforts superfluous. Most geoengineering measures are still at the stage of theoretical considerations. As a rule, therefore, no clear statements can be made about the effectiveness and timing of deployment, nor can the risks and side effects be validly assessed. The various geoengineering measures differ considerably with regard to their risk dimensions, controllability and reversibility. Therefore, each proposal has to be evaluated on its own against certain criteria.

Measures to remove CO2 from the atmosphere, which are complementary to urgently needed measures, are increasingly being discussed. The IPCC Special Report of fall 2018 makes it clear that to achieve the 1.5 degree target, measures are likely to be needed to remove CO2 from the atmosphere. One intensively discussed example is BECCS, which is the use of renewable resources for energy production in combination with CO2 capture and storage in the biosphere.

Combating climate change by storing CO2 in the seabed?

In view of the unchanged increase in global carbon dioxide emissions, the option of storing CO2 in geological formations deep under the sea should not be completely ignored. It could serve as a bridging technology until renewables and increased energy efficiency are sufficiently established. Undersea storage in geological formations is not without problems, as subsequent escape of the stored CO2 cannot be completely ruled out. This can happen due to technical deficiencies, accidents during transport, injection or the storage process, or the selection of an unsuitable storage formation. Leakage from subsea reservoirs can contribute to ocean acidification. Nekton (fish and cephalopods (cephalopods)) and plankton (unicellular algae) may be affected. Based on current knowledge, leakage rates < 0.01% per year appear to be acceptable under certain geological and technical conditions. This corresponds to a retention time of 10,000 years.However, there is a considerable need for research to validate this assumption.

The storage of CO2 in the seafloor

Storage of CO2 in the seafloor can occur in saline aquifers and in oil or gas reservoirs. When assessing potential leakage risk, it is important to note that CO2 occurs in varying densities depending on ocean depth. If CO2 leaks at a depth where it is present as a hydrate (>3,000 m), the least damage is likely. According to current knowledge, the storage of CO2 at this water depth is associated with a lower risk. The costs and corresponding effort for storage are probably significantly higher than for storage at shallower depths.Storage at shallow depths requires, because of the considerable upwelling of the carbon dioxide, a suitable caprock with consistently low

permeability. If leakage nevertheless occurs, the CO2 is dissolved in the water and contributes to ocean acidification. In the case of very large leakages, the CO2 can also reach the sea surface, where it then contributes to the enrichment of CO2 in the atmosphere.

To ensure that CO2 injected into saline aquifers and oil and gas reservoirs remains permanently harmless there, it must be stored for the long term (preferably for several millennia). Tests are currently being carried out on some natural and artificial reservoirs with regard to permanent storage safety. Potential safety risks are posed in particular by old, insufficiently sealed boreholes. Experience with the CO2 resistance of these borehole seals is naturally only available for a few decades. In addition to the borehole seals, attention must be paid to the pressure increase in the reservoir rock caused by the introduced CO2. It is essential to keep this within narrow limits in order to avoid mechanical damage to the cover layers. Risk assessments regarding the impermeability of the reservoirs should be based on experience with existing natural and artificial CO2 reservoirs.