Atmosphere changes

What is it
As the name suggests, global warming refers to the increase in the earth’s atmospheric temperature, which began in the late 19th century as a result of increases in greenhouse gases such as water vapor, carbon dioxide, methane and others. These greenhouse gasses are released into the atmosphere from fossil fuel combustion. This process and will continue indefinitely if there is no reduction in the rate of deforestation and emission of fossil fuels. Climate models predict that the earth’s temperature will increase by up to 6.4oC [1], depending on how much the emissions rate changes over the next century.

Why it matters to our oceans
Increased atmospheric temperature will also increase the temperature of the ocean. This will particularly affect shallow coastal marine ecosystems such as coral reefs where many tropical corals live near their upper thermal tolerance limits. Increase in water temperature causes ‘bleaching’, a condition where the corals expel their algal symbionts so the colonies appear white. Corals can only survive in the bleached state for a short period of time, after which they begin to die. Shallow reefs worldwide are already being degraded from extended bleaching events, and these are expected to get worse as ocean temperatures increase further. Increased temperatures will also cause an increase in sea level. How negatively this affects marine ecosystems depends how quickly this occurs and whether marine fauna can adapt to these shifts. Shifts in ocean temperatures may change faunal ranges so tropical species move further north, and cold water species may move deeper. Changes in ocean currents and weather patterns can disrupt patterns of productivity, which could affect food webs and result in reduced populations of prey fish and commercial species.

Why it matters to humanity
The sea level rise resulting from global warming will cause flooding or loss of some low-lying coastal communities and Islands. The Islands of the Maldives average only 1.5 meters above sea level, so with a predicted sea level rise of 59 cm, many of the islands will be underwater by 2100. [2]. Shifts in atmospheric and ocean temperatures will cause unpredictable changes in the range and abundance of seafood, and persistent high water temperatures will further degrade tropical coral reefs. Both of these consequences would reduce the amount of seafood for human populations, especially in tropical areas where coastal communities rely on reef species for the majority of their protein.

What is it and why it matters
Approximately one quarter of the CO2 that is released into the atmosphere is absorbed by the oceans [3]. When CO2 dissolves in seawater carbonic acid is formed, and through a complex series of chemical equilibria, also results in fewer free carbonate ions in the water. Skeletons and shells of important marine life such as corals, mollusks and crustaceans are made of various different types of calcium carbonate, which dissolves in acidic conditions. Not only does ocean acidification threaten to weaken the protective and supportive structures on many marine species, the fewer free carbonate ions mean that is becomes more difficult for animals to create skeleton. Some areas are more susceptible to acidification than others; for example the deep Pacific Ocean is naturally more acidic than the Atlantic, so further reduction in pH may push susceptible species to a point where they cannot create skeleton. This is of particular concern for the shellfish aquaculture industry in the US Pacific northwest, where frequent upwelling along the coast brings low pH deep water into their culture facilities and causes severe mortality in their larval oyster production. Deep coral reefs, especially in the Pacific are vulnerable to acidified conditions, as they build their skeletons from one of the more soluble forms of calcium carbonate (aragonite). The upper water column is saturated with aragonite, but deeper water is under-saturated. The depth at which the water becomes under-saturated is becoming shallower as the ocean absorbs more and more CO2. This shoaling of the aragonite saturation depth will eventually expose deep sea coral reefs to under-saturated conditions. At this point it becomes harder for the coral to build skeleton, and the dead colonies that create the reef infrastructure will begin to dissolve. The speed and scale of these impacts is not well understood, but if we do not reduce emissions, the consequences could be devastating.

What can be done to help
The only real solution to global climate change and ocean acidification is to greatly reduce the global scale of fossil fuel combustion, and reduce deforestation. Trees absorb CO2 and release O2, so forests mitigate for some of the CO2 released through combustion. This is an extremely challenging objective and has met with little success to date. Since acidified conditions are a result of elevated CO2, but there are other causes of elevated CO2 that occur on a local scale and that can also be addressed locally. Low pH can also occur in high nutrient areas, where runoff or riverine input has increased metabolism (respiration) of animals that take advantage of increased food supply. Reducing the nutrient load would also reduce bacterial respiration and CO2 production, making the water less acidic. Although this is a global problem, some effects can be mitigated on a smaller scale through good management practices that reduce nutrient-laden runoff into the ocean.

How Marine Protected Areas can help
Although MPAs cannot prevent the effects of global ocean acidification, they can help keep ecosystems healthy and more resilient to the impacts of changing water chemistry. Regulations that prevent human activities from degrading marine environments (through fishing, physical damage and removal of non-target species), help maintain them in a healthier condition so they can better withstand other stresses.

What you can do to help
Support MPAs or other regulations that help maintain healthy ecosystems.

[1] en.wikipedia.org/wiki/Global_warming

[2] en.wikipedia.org/wiki/Maldives#Environmental_issues

[3] en.wikipedia.org/wiki/Ocean_acidification