Climate Change in Our Ocean – Part 1

Every year humans pump almost ten billion tonnes of carbon into the atmosphere from the burning of fossil fuels 1 . Most of this carbon is in the form of CO 2 gas, which forms a thin blanket around the earth, holding in the sun’s energy and slowly warming the land, atmosphere and oceans.

In Australia, we are facing a warming double whammy from a combination of global average warming with increasing tropical water volumes travelling down both sides of the continent. These cumulative effects, combined with cyclical factors like El Nino and La Nina, mean Australian waters are fast becoming climate change hotspots2 . In March this year, South East Australian sea surface temperatures were already 2 °C above average3 , and in March 2011 South West Australian ocean temperatures peaked at a whopping 5 °C above normal 4. So much for the Paris global target not to exceed 2 °C warming!

A couple of degrees may not sound like much, but marine organisms are very sensitive to temperature. Whilst terrestrial temperatures vary in the order of 20 – 30 °C over a year, ocean temperatures in a given location vary by less than 10 °C 5 . Marine creatures need a more stable temperature regime; the optimum temperature range for reef corals, for example, is from 23 – 29°C, and they can bleach with just 1 °C increase6. Other marine invertebrates, fish and even seagrasses can be just as sensitive, with mortality, range shifts and life stage impacts resulting from as little as 1-2 °C warming7 8 .

Global warming has other flow-on effects. Increasing energy in weather systems leads to more severe, more frequent storms. Floods and cyclones are considered to be one of the most serious threats to our coral reefs9. Whilst a single stressor, such as a storm, may not result in mortality, the combination of multiple stressors (warming, storm damage and run-off) can result in long term losses10.

To compound the problem, only half of the CO 2 that we pump into the atmosphere stays there. The other half is absorbed chemically by the ocean, making it more acidic11. This creates issues for many marine organisms, particularly those that have shells. Many plankton make fine shells or platelets around themselves for protection, and these shells become increasingly difficult to produce. They even start to dissolve if the level of acidity becomes high enough.

Plankton form the basis of the oceanic food web which feeds everything from fish to penguins, seals and whales. Virtually every living organism is affected, either directly through body chemistry or indirectly through reduced food supply. Projections are that pteropods (sea butterflies) will be unable to make their shells in the Southern Ocean by 205012. Krill have declined in parts of the Southern Ocean by as much as 80% over 30 years13. Whales and penguins are forced to compete with a growing krill fishing industry for a declining resource; emperor penguin populations have halved over 50 years, and Adelie penguin populations have halved in a decade14.

The physical changes in our oceans are driving a mass migration of marine species towards the poles. Tropical species are turning up further south, changing the composition of marine communities15. We will explore this in more depth in our next article – for now let’s just say these tropical visitors aren’t always welcome!

On the positive side, we seem to be arguing less and less about whether climate change is “real”. But accepting reality is not enough. Action is needed, and the window of opportunity is closing fast. At an individual level, we make decisions every day that impact on our personal carbon emissions. At a political and commercial level, much more can be done to encourage sustainable, renewable energy and move away from fossil fuels.

There are also actions we can take in terms of marine conservation. Marine Protected Areas provide much-needed resilience to the effects of climate change; they can’t stop warming and acidification, but they can help marine life to cope. Reducing other stressors, such as chemicals, nutrients and sediment in terrestrial run-off is also important particularly for our coral reefs.

There is no escaping climate change and our responsibilities; we created this problem – it’s up to us to fix it.

This article is originally published in AMCS Turning the Tide

2 Hobday and Pecl (2014) Identification of global marine hotspots: sentinels for change and vanguards for adaptation action. Reviews in Fish Biology and Fisheries, June 2014, Volume 24, Issue 2, pp 415-425
4 Pearce, Lenanton, Jackson, Moore, Feng and Gaughan (2011) The “marine heat wave” off Western Australia during the summer of 2010/11. Government of WA, Department of Fisheries
7 Peck, Webb and Bailey (2004) Extreme sensitivity of biological function to temperature in Antarctic marine species. Functional Ecology 2004 18, 625–630
8 Cheung, Watson and Pauly (2013) Signature of ocean warming in global fisheries catch. Nature 497, 365–368 (16 May 2013)
10 Bann, Graham and Connolly (2014) Evidence for multiple stressor interactions and effects on coral reefs. Glob Chang Biol. 2014 Mar;20(3):681-97
11 Pickrell (2004) Oceans Found to Absorb Half of All Man-Made Carbon Dioxide. National Geographic News
12 Bednarsek et al (2012) Oceans Found to Absorb Half of All Man-Made Carbon Dioxide. Nature Geoscience 5, 881–885
13 Brower (2013) Life in Antarctica Relies on Shrinking Supply of Krill. National Geographic
14 Roach (2001) Penguin Decline in Antarctica Linked With Climate Change. National Geographic News
15 Johnson et al (2011) Climate change cascades: Shifts in oceanography, species’ ranges and subtidal marine community dynamics in eastern Tasmania. Journal of Experimental Marine Biology and Ecology 400 (2011) 17–32

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