EXPERT REACTION: The GBR may never fully recover from 2016's heatwave

The results of this study confirm our worst fears of the detrimental impact man-made climate change is having on the Great Barrier Reef, and our natural ecosystems as a whole.

As human influence on the climate increases, so too will the intensity, frequency and duration of marine heatwaves that cause this sort of devastation.

Globally, we have already seen a 34 per cent increase in the frequency of marine heatwaves, and 17 per cent increase in their duration. Unfortunately these increases in marine heatwaves are much faster than the recovery time of coral reefs themselves.

The future is looking bleak for coral reef ecosystems, as well as the services and economies that rely on them.

This is yet another concrete example of the costs of climate change. The science is clear. We are doing massive damage to the Great Barrier Reef, and there is justifiable concern that some of the damage might be irreversible. A unique, global feature is being destroyed on our watch.

This is not just an environmental disaster, but also a serious economic issue. Reef tourism employs far more people and generates far more revenue than the coal industry.

A government that was looking ahead would be managing a rapid transition to clean energy. This would allow Australia to play a leading role in the global move to a low-carbon future, the only hope of saving the Great Barrier Reef.

Instead, the proposed National Energy Guarantee would effectively end large-scale wind and solar construction in 2020.

In contrast to Australia’s political inertia on energy and climate, global warming relentlessly degrades our greatest marine asset, the Great Barrier Reef.

In just a few years, close to half the shallow corals of the reef have been lost and with them a vast, vital platform for Queensland’s coastal regional economy.

Ignoring the science endangers further the reef’s resilience, and with it the enormous ecological, economic and social contributions it makes to our world.

In regional development terms, the death of the GBR remains the greatest threat to realising sustainably the potential of northern Australia.

This paper thoroughly documents the impact of marine heatwaves on coral reef ecosystems. 

When considering these conclusions, we should keep in mind that the conditions experienced in 2016 and 2017 are likely to become the new normal within decades.

Heatwaves are transient features that are linked to anomalous weather events or, if prolonged, to climate variability, such as the El-Nino Southern Oscillation. The most pronounced heat waves in the ocean are associated with variations of the dynamics of western boundary currents, such as the East Australian Current.

As such, an individual heatwave triggering coral bleaching cannot be linked to global warming as the process triggering an individual heatwave is fundamentally different from that triggering global warming. The claimed link between the 2016 heat wave and global warming has no scientific basis.

The claim that the GBR will not recover in the future cannot be tested yet. Unfortunately, the scientific method insists that we have wait several decades before we can scientifically conclude that the GBR has or has not recovered from the 2016 heat wave. Speculation should not be the highlight of a research study.

Indeed, the above argumentation cannot be turned upside down to argue that there is no global warming. Such a statement would not be supported by the overwhelming scientific evidence that exists.

I don't dispute the scientific findings of the study. Instead I call for more scientific rigour and caution in the formulation of conclusions.

UPDATED: We know for some time that the reef is under threat – on short timescales (weeks to months)  from marine heat waves, on medium time scales (seasons) from eutrophication, and on  longer times scales (decades) from ocean acidification (global warming).

On the other hand, climate variability (such as El Nino events) sets the background temperature level on periods of several years (and may lower the short-term effect  of a heat wave).

While an individual heat wave cannot be attributed to global warming, and this is really irrelevant, it is sad to see that a marine heat wave can cause such widespread damage.

These results highlight the potential for climate change to transform ecosystems.

Increasing levels of climate change are likely to see such ecosystem transformations around the world in the oceans, at the coast right through to the tops of mountains.

The challenge this presents to managers, scientists, policy makers, and society more broadly is, what does it mean to conserve ecosystems while the species and processes within them change dramatically?

The societal expectations, policy and knowledge bases that underpin the way we currently conserve nature are derived from an assumption that while species and ecosystem may fluctuate, they should not change dramatically.

Observations of current climate change, exemplified by this study, and innumerable explorations of future impacts to species and ecosystems, show ecological transformation is occurring and has the potential to become widespread.

To cope with this we need new expectations, knowledge and conservation programs that focus on those aspects of nature that can persist through change and are valued by society.

In 2003, a collaboration between CSIRO and the Australian Institute of Marine Science developed a reef bleaching model, ReefClim, that simulated five stages of bleaching from heat stress through to catastrophic bleaching, where recovery from the latter was projected to take decades.

It used total degree days over a bleaching threshold to measure the severity of bleaching. The critical bleaching level for sea surface temperatures was reached when the risk of future bleaching showed the next event was likely to occur before recovery from the last event. This paper measures heat stress the same way.

The level of damage the authors describe show that some areas of the northern reef will take decades to recover.

Sea surface temperatures from October 2015 over the whole of the Great Barrier Reef are 0.55°C higher than they were from summer 1998 to winter 2015. If the reef has moved into a new temperature regime compared to the one that existed between 1997 and 2015, parts of the reef will now be subject to critical levels of bleaching, if they were not already.

This suggests the authors have been conservative in their conclusions, as devastating as they are.