Dr Willow Hallgren
As human activity contributes more and more greenhouse gases to the atmosphere, such as CO2 and methane, this is having a major impact on the world’s oceans. The oceans have taken up around 40 per cent of the carbon dioxide emitted by humans since 1750 – the beginning of the industrial revolution.
Absorbing so much CO2 is making seawater increasingly more acidic, and this will, increasingly, cause the shells and skeletons of some marine creatures, including corals, plankton and shellfish, to dissolve. The oceans have also absorbed about 90 per cent of the warming caused by human carbon emissions since pre-industrial times.
This warming and acidification of the oceans is having profound impacts on both its physical structure and the myriad lifeforms who live in it and depend on it, including humans. It is also having major impacts on Australian fisheries, aquaculture and tourism.
Threat to coastal properties
The oceans are getting warmer and expanding, causing sea-level rise (along with land-based ice sheets melting). Coupled with more severe storms, this means that storm surges are increasingly inundating low-lying coastal areas, leading to disruptive and expensive flooding events. Extreme sea levels have occurred three times more frequently in the second-half of the 20th century than the first-half. Moreover, the rate of sea-level rise is increasing, and is predicted to rise at a considerably faster rate during the 21st century than it did during the 20th century.
Currently, there are hundreds of beaches and coastal communities around Australia that are at risk from coastal erosion. A few more decades of sea-level rise, and this number could climb into the thousands. The global average sea-level is predicted to rise by 45 to 82cm (above levels seen in the late 20th century) in the next 70 years – if we continue emitting large amounts of greenhouse gases. Of course, if any of the land-based ice sheets continue to melt unabated, the sea-level rises could be much larger, threatening the lives and livelihoods of millions of people living around the world’s coastlines. Both the Greenland and West Antarctic ice sheets are melting at record rates – and accelerating!
Needless to say, beach-front or low-lying waterfront property is probably not a good long-term investment. The burgeoning coastal development around Australia will undoubtedly face increasing risk due to storm surges and extreme water levels as greenhouse gas emissions continue to climb.
See the Great Barrier Reef before it’s gone
As communities around Australia are reeling from the unimaginably devastating ecological catastrophe of an unprecedented bushfire season, there is another ecological catastrophe unfolding, albeit at a slower rate. In the seas that gird our bushfire-burnt country an ecosystem with immense biodiversity and beauty – the Amazon rainforest of the ocean; the Great Barrier Reef (GBR) – is dying. Its death is both predictable and inexorable if the continued rise in global CO2 emissions is not halted.
Australians have now realised that the 2008 predictions of climate-change-induced severe bushfires by 2020, in the Garnaut Climate Change Review should have been listened to and acted upon. The devastating results are now all around us and have been choking us in both the countryside and the cities for months.
What Australian’s must also recognise is that ignoring the warnings about climate change and the GBR will have massive and possibly irreversible consequences. Between 1985 and 2012 there was a 50 per cent decline in coral cover due to human influences, and this occurred before the back-to-back massive coral bleaching events of 2016 and 2017, which devastated nearly half of the Great Barrier Reef. In 2019, a scientific study found an 89 per cent decline in the number of new corals settling on the Great Barrier Reef.
We must realise that the future of the GBR is now dependent on how quickly greenhouse gas emissions come down. If we keep global temperature rise to 1.5 degrees, the reef will survive, but in a degraded state, with less coral cover and less biodiversity. However, if greenhouse gas emissions continue to rise on their current trajectory, then it’s ‘game over’ and the reef will die completely, according to Professor Terry Hughes, the director of the ARC Centre of Excellence for Coral Reef Studies..
The times they are a’changing
So what can we do to mitigate and adapt to the impacts of climate change on the oceans? First of all, vote for a party that has strong policies on emissions reduction – not for parties who try to use sneaky carbon accounting tricks to get away with doing as little as possible to address the root cause of climate change.
In 2018, climate change scientists agreed that ‘limiting global warming to 1.5°C would require rapid, far-reaching and unprecedented changes in all aspects of society… Global net human-caused emissions of carbon dioxide (CO2) would need to fall by about 45 per cent from 2010 levels by 2030, reaching ‘net zero’ around 2050’.
Needless to say, Australia is not on-track to even come close to this level of emission reductions, yet this is what the science says we must do to avoid more frequent climate catastrophes, such as the 2019/2020 bushfires, or mass coral bleaching events. This is the same science that predicted the recent horror bushfire season only 12 years ago.
Rethinking where we live
Beach nourishment may be able to extend the habitability of eroding coastlines, but not forever. It’s really time we start to rethink human settlements in low-lying areas – we should be aiming for an organised, well-planned retreat. This must be accompanied by the replanting of coastal ecosystems, such as mangroves and seagrasses, to buffer coastlines from stronger storms and to preserve as much coastal marine-life as possible. Ultimately, the uninsurability of beachside properties might be the deciding factor on future coastal developments and a planned retreat away from low-lying coastlines (the market can be an efficient tool if we allow it to be – hello carbon tax!).
Plenty of heating to come
Unfortunately, due to past emissions, there is already considerable heating of the planet in the pipeline. It’s not going to be enough to simply stop emitting greenhouse gases. We need to sequester as much CO2 as we can, in order to stabilise the climate as much as possible and limit future impacts. Although ecologically risky, many marine geoengineering mechanisms have been proposed, such as fertilising the ocean with iron filings or other nutrients to stimulate phytoplankton growth, and growing kelp forests – which grow very quickly and absorb huge amounts of CO2.
Other ways the oceans might help us fix the problems we have created involve tapping into their enormous potential for renewable energy in the form of wave and tidal energy, and offshore wind farms. Reducing our reliance on fossil fuels, and diversifying the types of renewable energy we can draw on are our best approach to securing our long term, sustainable, relatively inexpensive energy future.
Dr Willow Hallgren is an earth-system scientist who studies the impact of climate change on ecosystems and biodiversity, the feedbacks between vegetation and the climate, and how policy can influence climate change, by changing how we use the land.
Willow has previously worked as a climate and biodiversity scientist in government, industry, and academic roles in both Australia and the USA at the Massachusetts Institute of Technology (MIT). She was also previously the Science editor of Monash University’s student newspaper Lot’s Wife.
She is a city escapee of many years now and is currently hiding out among the hill tribes of the beautiful Tweed Valley.
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