Understanding the Impact of Climate Change on our Oceans

Dr Anjani Ganase, marine scientist and environmentalist, explains climate change, and how its effects may appear in different places at different times, or not at all in some other places. Understanding climate change and its effects is urgent for small island states.

Over the years, discussion of human-induced global warming has slowly transitioned to climate change as scientists began to realise the broader effects of industrial carbon dioxide (CO2) emissions on our planet. While global warming refers specifically to the increase in global temperatures of the atmosphere and oceans, (as a result of the heat trapping capabilities of carbon dioxide emissions - the green house effect), climate change refers to the many other changes directly as a result of CO2 or because of the rise in atmospheric and oceanic temperatures. Some other physical phenomena that are occurring as a result of higher CO2 levels and/ or rising temperatures include changes to the physical and chemical nature of the ocean.

THE WATER CYCLE

As water heats up, it evaporates from the surfaces of oceans, lakes and rivers and enters the atmosphere as water vapour to form clouds. As the water vapour moves to cooler locations, it returns to earth as precipitation such as rain and snow. The ocean, a major absorber of heat energy has shown significant increases in temperature in the top 700 m of the ocean since the 1970s. Warming surfaces of the oceans result in higher evaporation of water and therefore more water vapour in the atmosphere. When this water vapour cools, high in the atmosphere, this results in more intense rain or snow fall. Future predictions suggest that the current precipitation patterns will intensify as the climate warms. In other words, dry places are likely to become drier with prolonged droughts, and wet places are likely to become more prone to flooding or heavier snows, while other places may not be affected at all. 

Overlooking Charlotteville, Tobago on a clear day. Photo credit: Anjani Ganase

SEA LEVEL RISE

The anticipated sea level rise over the long term results from the loss of sea ice (Arctic) and glaciers worldwide, as well as ice sheets, frozen lakes, frozen ground and snow melt flowing into the oceans as temperatures warm. In addition, a proportion of the sea level rise is also attributed to the expansion of water at warmer surfaces. The latest Intergovernmental Panel for Climate Change (IPCC) report has stated that there is more than a 90 % probability that the rate of sea level rise has nearly doubled over the last 20 years compared to the previous century. However, sea level rise is not uniform as when you fill up a bathtub. The ocean circulation and variable wind intensities result in great regional disparities regarding sea level rise, especially when considering shorter time spans or regional scales. Coastal areas - low lying coastal ecosystems, mangroves, swamps and even cities - will be subject to saltwater flooding and damage to infrastructure during extreme events and high tides. In low-lying areas, there may also be loss of fresh (ground) water as salt water rushes inland.

A panoramic view of waves breaking on Englishman’s Bay, Tobago. Photo credit: Anjani Ganase

OCEAN ACIDIFICATION

The current concentration of CO2 in the atmosphere is estimated to be higher than what the earth has experienced in the last 800,000 years. This is the result of burning fossil fuels over the last 250 years. The oceans absorb a large portion (30%) of the CO2 emitted into the atmosphere, effectively buffering rising temperatures. However, this results in significant changes in the ocean’s chemistry. Long-term data has shown that higher concentrations of carbon dioxide in the ocean correspond with the decline in the ocean’s pH (by about 0.1 from an average pH of 8.2 across most of the world’s oceans since pre-industrial time in the 1900s). When CO2 dissolves in water it forms carbonic acid, subsequently the hydrogen ions from the acid tend to bind to other ions including carbonates, lowering its availability in the water. Carbonate ions are a crucial raw material used by many marine organisms – including crustaceans and hard corals – to make calcium carbonate (limestone) for their shells and skeletons, Future predictions for sustained absorption of CO2 in the ocean may not only limit shell and skeleton building but may result in dissolving of existing calcium carbonate frameworks. 

Coastal communities in Tobago, such as Castara Bay (shown here), depend on the ocean and coral reefs for food, storm protection and as a source of economic income. Photo credit: Anjani Ganase

REGIONAL RESPONSES

Although global trends point to rising temperatures, sea level rise and ocean acidification, these trajectories are certainly not uniform across all regions. This makes it all the more important to understand variations to assess and plan for the impacts of climate change in our own region. The IPCC reports focus on local research in order to mitigate expected impacts of climate change in any territory. For the South American region, it is expected that there will be greater freshwater flow into South American rivers, and therefore the ocean, because of increased precipitation, as well as due to ice melt from the Andes. Coastal areas such as mangroves and fresh water ecosystems are also likely to become degraded from saltwater intrusion. For small-island nations like Trinidad and Tobago, there may be significant changes to the fresh water resources and the ecosystems and communities that rely on those resources. Coastal erosion and flooding are expected with rising sea levels. 

It may be overwhelming to learn about the impacts on the environment and our homes as a result of climate change; especially as we now know that the only way to combat this is to significantly reduce carbon emissions. We all have parts to play in this reduction. As individuals, we do this by reducing consumption of energy, materials such as plastics, and by recycling. As communities, we must put pressure on governments, through those who represent us to transition away from fossil fuels and invest in renewable technology. As an industrial nation, we must lobby for cleaner and more efficient use of oil and gas resources.

References:

Much of the information expressed in the article is taken from the reports of the Intergovernmental Panel for Climate Change - IPCC (Rhein et al. 2013). The IPCC is an international body of scientists set up in 1988 that has produced scientific consensus reports about climate change regularly since then. New scientific information and models for future predictions on climate change are continually assessed and updated in the reports and used to understand the impacts on our environments and livelihood. This is a massive voluntary effort, undertaken by hundreds of scientists and leading experts across multiple fields worldwide (environment, social and political) to compile, review and collate the published scientific data. The reports offer a balanced outlook of climate change based on the best regional and global evidence along with advice on mitigating its effects. These reports are freely available to public and government. http://www.ipcc.ch/index.html

Rhein, M., S.R. Rintoul, S. Aoki, E. Campos, D. Chambers, R.A. Feely, S. Gulev, G.C. Johnson, S.A. Josey, A. Kostianoy, C. Mauritzen, D. Roemmich, L.D. Talley and F. Wang, 2013: Observations: Ocean. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.