The ocean’s impact on climate


The oceans play a very critical role in climate change, and it’s time we understood that, says Karn Ragade, as he explains the dynamics.

Oceanic climate is a climate which generally features cool summers and fairly cool winters. This is often seen on west coasts with higher middle latitudes of continents. The technical definition of oceanic temperature would be, a climate having a monthly mean temperature of below 22oC in the warmest month, and above 0o C in the coldest month.

This typically lacks a dry season as the precipitation is evenly dispersed across the year. Oceanic climates can have much storm activity as they are located in the belt of the stormy westerlies. Many oceanic climates have frequent cloudy or overcast conditions due to the near constant storms and lows tracking over or near them. The annual range of temperatures is smaller than typical climates at these latitudes due to the constant stable marine air masses that pass through oceanic climates, which lack both very warm and very cool fronts.

Ocean and climate change
The ocean is an important component of the climate system. It provides the surface temperature boundary condition for the atmosphere over 70% of the globe. It provides 85% of the water vapour in the atmosphere. It exchanges, absorbs and emits a host of radiatively important gases. It is a major natural source of atmospheric aerosols. However, the ocean is dynamic and its surface properties will vary on all time scales, allowing great scope for feedback between the ocean and atmosphere.

Over the last two decades, the importance of the ocean to understanding, and predicting the evolution of the climate system has been recognised. Now, a climate model needs to possess a coupled ocean and atmosphere to be taken seriously, because oceanic processes, through the ocean’s thermal and dynamic inertia, intrinsically contain the long time scales on which climate changes.

How oceans affect climate
Sea level rise: The heat capacity of the oceans provides a thermal lag on the climate. The heat capacity depends on the parts of the ocean that are involved; for time scales from seasonal to decadal, the ocean mixed layer is dominant, whereas for millennial time scales, the interior ocean is also important, and the ‘effective’ heat capacity is larger, perhaps 50 times that of the mixed layer alone (Wigley and Raper, 1991). Actions by us have accelerated this rate of thermal lag and this is in turn increasing the heat capacity of the oceans, which is what is causing the ice caps to melt, thereby causing the rapid increase in sea levels.

The Arctic: In the winter of 2006, huge amounts of warm, salty water suddenly flowed into Kongsfjorden in Svalbard. The warm Atlantic water changed the composition of the plankton community in Kongsfjorden. Small Atlantic zooplankton with low energy content swept in and replaced the large, energy-rich arctic zooplankton species, which only thrive in cold water.

This sudden climate change in Kongsfjorden set up a chain reaction in the food web. Both black-legged Kittiwakes and Little Auks rely on energy-rich prey to feed themselves and their chicks. Such food is plentiful in nutrient-rich Arctic waters. When water temperatures in Kongsfjorden rose several degrees, kittiwakes and little auks had quite different food on their plates.

The climate change in Kongsfjorden had impact on both these seabird species, but in different ways. The altered availability of food primarily hit the Little Auk. The Kittiwake managed better, making use of the capelin the water masses had brought. But the two species’ metabolism also reacted differently to the changes.

In spring and summer, the oceans of the Arctic are extremely productive; masses of different seabirds and sea mammals come to the Arctic to feed on zooplankton and small fish. Changes in the marine environment in the Arctic can thus affect species that spend much of the year elsewhere. A wide range of alterations in the Arctic marine environment have been shown to be caused by climate change. For example, some sub-Arctic species and a few from temperate regions have experienced a northward shift in habitat. This led to changes both in the occurrence of key species and in the food web. Simultaneously, the occurrence and reproductive rate of some arctic species declined, especially the ice-dependent species.

In the last 100 years, average global temperature has increased by 0.74°C, rainfall patterns have changed, and the frequency of extreme events increased. Change has not been uniform on either a spatial or temporal scale, and the range of change, in terms of climate and weather, has also been variable.

There is documentation showing increased primary production in open water in the Arctic Ocean. Overall, available studies imply that the effects of climate change arise mainly through increased inflow of warm water from the Atlantic and Pacific oceans to the Arctic Ocean, longer residence time for these warm water masses, and changes in sea ice, rather than through direct warming.

In the last 100 years, average global temperature has increased by 0.74°C, rainfall patterns have changed, and the frequency of extreme events increased. Change has not been uniform on either a spatial or temporal scale, and the range of change, in terms of climate and weather, has also been variable. Ocean acidification, climate change and global warming are just some of the extreme level events that are heading our way. Scientists believe that an increase in one degree in global temperature can cause major shifts in the sea levels, causing ice in the glaciers to melt and submerge a fairly large amount of our coastline. From a two degree to six degree change in global temperature, we can expect the next desert to be in Australia, and the now Sahara desert to be the next Savannah grassland. This type of paradigm shift in the geographical structure of the Earth means that we are nearing the next mass extinction.

A few key impact of climate change on marine environment are very well elucidated from the WWF Panda organisation on their website:
Coral bleaching: One of the most visually dramatic effects of climate change is coral bleaching, a stress response caused by high water temperatures that can lead to coral death. Recent years have seen widespread and severe coral bleaching episodes around the world, with coral mortality reaching 70% in some regions.

Stormy weather: Most scientists believe that global warming will herald a new era of extreme and unpredictable weather. Tropical storms and heavier rainfall may increase, and so too would the consequent physical damage to coral reefs, other coastal ecosystems, and coastal communities. Hurricanes Hugo and Marilyn hit the US Virgin Islands National Park in 1989 and 1995, respectively, and did massive damage to coral ecosystems.

As the oceans warm, the location of the ideal water temperature may shift for many species. A study has shown that fish in the North Sea have moved further north or into deeper water in response to rising sea temperatures. Other species may lose their homes for other reasons. The distribution of the penguin species in the Antarctic peninsula region, for example, is changing with reduction in sea ice due to global warming.

Altered lifestyles: Rising temperatures can directly affect the metabolism, life cycle, and behaviour of marine species. For many species, temperature serves as a cue for reproduction. Clearly, changes in sea temperature could affect their successful breeding.

The number of male and female offspring is determined by temperature for marine turtles, as well as some fish and copepods (tiny shrimp-like animals on which many other marine animals feed). Changing climate could therefore skew sex ratios and threaten population survival.

Rising sea levels: Global sea levels may rise by as much as 69 cm during the next 100 years due to melting of glaciers and polar ice, and thermal expansion of warmer water. Rising water levels will have serious impacts on marine ecosystems. The amount of light reaching offshore plants and algae dependent on photosynthesis could be reduced, while coastal habitats are already being flooded. Rapid sea level rise will likely be the greatest climate change challenge to mangrove ecosystems, which require stable sea levels for long-term survival.

Decreased mixing: Vertical mixing in the ocean is important for many reasons, including transporting nutrients from deep to shallow waters, and surface water rich in oxygen into deeper waters. In some areas, changes to ocean temperature profiles induced by climate change are causing a reduction in the amount of mixing, and for example, reducing oxygen levels at depth.

Acidic oceans: After absorbing a large proportion of the carbon dioxide released by human activities, the oceans are becoming acidic. If it weren’t for the oceans, the level of carbon dioxide in the atmosphere would be much higher.

The effect could be that fish, squid, and other gilled marine animals may find it harder to “breathe”, as the dissolved oxygen essential for their life becomes difficult to extract, as water becomes more acidic. And shellfish, crabs, lobsters, and corals may find it more difficult to build their calcium carbonate shells. In some areas, calcium carbonate shells may even start to dissolve.


Karn Ragade

Karn Ragade is a faculty member of English Language and Literature for the Middle Years Programme at the prestigious Victorious Kidss Educaress, a model IB school in Pune. He has spent many years in social service. He continues to pursue his interest in the same by volunteering with organisations to rekindle maritime awareness among masses, and also by supporting basic first-aid training.