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Monday, April 11, 2016

Attenborough on the Great Barrier Reef, sea level rise and climate change

Did you watch the first part of David Attenborough's documentary on the Great Barrier Reef?

This is a remarkable documentary with filming ending just as the reef was undergoing massive coral bleaching due to exceptionally warm waters caused by climate change. This is the third global coral reef bleaching event on record.

Attenborough first visited and documented the reef 60 years ago. Part one of the three part series contains an allegorical story from the Cairns area about sea level rise from the aboriginal dreamtime.

The Great Barrier Reef, geologically speaking, is a relatively recent phenomena. Sea levels were 70 to 90 metres lower during the Ice Age period with a narrow and steep shoreline where the east coast of Australia fell sharply to deeper waters. Sea levels started to rise at the end of the last ice age about 14,000 years ago.

About 10,000 years ago it started innundating large areas of coastal plain and wetlands which became the continental shelf. The shallow waters encouraged the growth and proliferation of corals along the vast stretch of the Queensland coast. The average depth of this continental shelf is about 35 metres. At that depth there is still enough light to penetrate to stimulate reasonable coral growth, making an ideal environment for the growth of the largest living structure on earth.

Near Cairns in North Queensland the edge of the continental shelf is about 50 kilometeres away from the present coast.

As David Attenborough told us, "Amazingly, at 10,000 years ago there was no coral here at all. The Great Barrier Reef, as we know it today, simply did not exist. How and when these coral communities began is how scientists are just beginning to investigate....Their research has helped identify an event 10,000 to 20,000 years ago, which may explain how the Great Barrier Reef was formed. But surprising, scientists are not the only ones to tell this story."

Dreamtime stories tell of sea level rise

Human occupation in Australia dates back to perhaps 50,000 years. The Googanji and Yidinji peoples are living in the region, near present day Cairns for much of this time. They witnessed first hand the sea level rise which innundated the coast line from about 13,400–7,500 years Before Present. And they have dreamtime stories which narrate this change in sea level as part of their oral lore and culture past down for millenia.

David Attenborough tells us about the Gimuy Walubara Yidinji people of the Cairns area who continue to dance and sing the dreamtime stories about totems, the coastal flatlands and the drowning of the coastal lands.

"This community has dwelt alongside the reef for thousands of years, and many of their traditions hark back to those ancient times. One of them tells how the reef came into existence. It is a legend that has been passed down from generation to generation in the form of a dance." narrates Attenborough.

David Attenborough interviewed one of the scientists on board the Alucia research ship. It is an interesting interchange:

David Attenborough: "Roughly 14,000 years ago the climate started to dramatically change."

Scientist: "It was the end of the ice age, and all that water started to innundate the continental shelf, to flood this vast flat landscape"

David Attenborough: "In one man's lifetime?"


David Attenborough: "So people living here are going to have to retreat?

Scientist: "Absolutely. It would have been a dramatic time for them. They would have been following the coastline as it prograded further and further back as the water was flooding the shelf. The rate of change was so great that in these very flat areas here, the coastline would have moved back hundreds of metres every year.

David Attenborough: "Every Year?

Scientist: "Every Year!

David Attenborough: "Gosh. That is formidable."

A 2014 conference paper by three Australian researchers revealed a number of stories from around the coast of Australia of the sea level rise event ocurring at the end of the last ice age. A Scientific American article spread this research to a much wider audience. Charlotte Hajer has a particularly interesting blog on 10,000 Years of Oral Narrative. You can read Nick Reid and Patrick Nunn, two of the three authors of this study, explain their paper at The Conversation: Ancient Aboriginal stories preserve history of a rise in sea level.

One of the examples in the research was from Fitzroy Island in the Cairns area from the Googanji people, related to the Yidinji people that Attenborough featured. Here is the excerpt on Fitzroy Island

The present geography of the area is shown in Figure 3A. For Fitzroy Island to be connected to the mainland, as the latter tradition states, the sea level would need to be 23-25m lower than today. For the coast to be 'where the barrier reef now stands', it is probably necessary for sea level to be at least 50m lower than today, depending on what people recognised as the 'barrier reef'.

It has been argued that during the Last Glacial Maximum, when what is now the Great Barrier Reef was emergent, the coast would have been bordered with cliff-line and unattractive to humans (Bowdler, 1995). Only later, as sea level rose over the edge of the continental shelf and a lowland terrestrial landscape developed that was both easy to access and contained diverse ecosystems, might people have been encouraged to occupy the area (Figure 3B). If the stories quoted, and the others that Dixon (1977) alludes to, recall a time when the coastline was at the Great Barrier Reef, these would have to date from a time when sea level was perhaps somewhere in the range 30-65 m below present. As shown in Figure 3, most of the shelf/reef off Cairns would have been dry land when sea level was 65m lower, yet large parts of the area would still have been emergent when sea level was 30m lower. Much depends on how modern storytellers conceptualise what is and what was formerly meant by the (barrier) reef. The large range of former sea levels results in a large range of minimum ages for these particular traditions: 10,450-9,900 years BP if they refer to a time when sea level was 30m lower; 13,400-12,600 years BP if they refer to a time when sea level was 65m lower (see Figures 3B and 4)

Several metres of sea level rise

The latest research by DeConto and Pollard (2016) advises that we may see sea level rise of up to two metres this century, due to the interaction of ocean warming and the Antarctic Ice sheet. This study incorporates two processes: hydrofracking and ice wall collapse, that have not previously been included in the dynamics of ice sheet collapse models.

But even this is not the worse case scenario, with Hansen et al (2016) saying that several metre rise may be possible due to the abrupt rate of change and lack of action so far in rapidly reducing global Greenhouse gas emissions. We know these rates of sea level rise are possible through examining paleo climate history. Large sea level rise rates are possible with natural climate change orders of magnitude less than the current rate of climate change. That is scary.

Towards the end of this century we may be experiencing sea level rise equivalent to, or even greater than, what the Googanji and Yidinji peoples experienced 10,000 years ago.

Although with our consumer lifestyle and infrastructure it is going to be much more difficult to pick up everything and migrate inland.

Of course Australia's Environment Minister played up hopes for the reef early in the week telling the Courier Mail, “The key point that I had from seeing the first of the three parts is that, clearly, the world’s Great Barrier Reef is still the world’s Great Barrier Reef,”

The Guardian reported on how silly this comment was in the context of the current bleaching event. Over 95 per cent of the northern and most pristine part of the Great Barrier Reef was found to be severely damaged according to an aerial survey. It is estimated that damage is so severe that 50 per cent of this coral may not recover and will die. The Bureau of Meteorology said that this summer’s sea temperatures were the hottest on record for Australia.

The Guardian article quoted Attenborough, “The twin perils brought by climate change – an increase in the temperature of the ocean and in its acidity – threaten its very existence. If they continue to rise at the present rate, the reefs will be gone within decades. And that would be a global catastrophe. About a quarter of the species of fish in the world spend some part of their lives in the reefs. If the reefs go, the fish will also disappear. And that could affect the livelihood and diet of human communities worldwide.”

Hunt has emphasised that water quality on the reef has been improving, yet in 2014 the water quality remained poor. Australia is unlikely to meet water quality targets designed to protect the Great Barrier Reef, researchers from the Australian Institute of Marine Science (AIMS) have warned in April 2016.

Watching the death spiral of the Great Barrier Reef

As much as improving water quality and providing marine reserves will increase reef resilience, the destruction and extinction of most of the coral reef system is already on the cards. Corals can recover from damaging events such as marine heatwaves and storms, but it often takes up to 10 years. With rising global temperatures marine heatwaves will occurr more often sending reef systems into a death spiral.

I have followed some of the scientific studies and pleas by marine scientists for rapid emissions reduction as a necessity for saving reef ecosystems. Appeals, such as this consensus statement from 2007 or this 2009 scientific call for emissions to be slashed to save the reef, have largely fallen on deaf ears of politicians, many who are already in the pocket of coal and mining interests.

I recently wrote this comment on the Guardian article: Greg Hunt rebuked by Attenborough film-maker after upbeat verdict on Great Barrier Reef

Whether you like it or not, the rich bio-diversity of the Great Barrier Reef ecosystem is probably headed for extinction. We are on a death watch, although few admit as much. The vast majority of coral reef systems are unlikely to survive warming this century simply due to the vast inertia in the climate system. At atmospheric warming of 2 degrees C, about 90 per cent of coral system will die. To preserve greater than 10 per cent of coral reefs worldwide would require limiting global warming to below 1.5 °C, and we have long past that point of being able to limit warming to 1.5C. The window on limiting warming to 2C is fast closing. See ‘Limiting global warming to 2 °C is unlikely to save most coral reefs’ (Full paper ). I wrote an article on this paper and other related coral reef issues in 2012.

Also Coral reef ecosystems acidifying 3 times faster than open ocean is another substantial concern.

Experimental observations of coral in a high CO2 world from the Lizard Island research station on the Great Barrier Reef, and from high CO2 natural environment around volcanic vents in Milne Bay, Papua new Guinea show that most corals are unlikely to survive.

So on the current emissions pathways, most coral reef ecosystems are headed for extinction, to be replaced by less diverse algae and seaweed based systems. With their demise will go much of the biodiversity of fish species. It is only a matter of time. We are all part of this extremely sad death watch!

  • Nicholas Reid, Patrick Nunn and Margaret Sharpe, Indigenous Australian Stories and Sea-Level Change (2014) (abstract) Conference Paper, 18th Conference of the Foundation for Endangered Languages (FEL): Indigenous Languages: Value to the Community, Okinawa, Japan 17-20 September 2014

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