|Charlie Veron has identified a third of all known coral species|
Global warming impacts right now are beyond some of the worst scientific predictions, so what does that mean for aspirations to save the Great Barrier Reef?
On 6 July 2009, Australian Dr Charlie Veron — who has discovered, described and identified about a third of all known coral species — addressed the Royal Society in London and asked: "Is the Great Barrier Reef on death row?" His response: "The answer must be yes… a close look at this question from any rational perspective arrives at the same bottom line: the Great Barrier Reef can indeed be utterly destroyed, and this could easily happen in the lifetime of my children."
It is a devastating answer because corals have been around for almost 500 million years and have formed more fossils than any other species, they are home to one-quarter of marine fish species, and tens of millions of people depend on reef ecosystems for protein and other services. The Great Barrier Reef (GBR) is home to 600 different types of corals, and is more biodiverse that any other UNESCO World Heritage site.
Now, in 2016, we have seen why Charlie Veron was so worried, with mass coral bleaching unprecedented in scale and severity occurring across the Reef in March. It was driven by a 1°C rise in sea temperatures compared to the recent average (2002-2011). Worryingly, there's little sign that those sea temperatures are returning to normal in the short run, so more damage may still be occurring.
Of 911 reefs surveyed by scientists since the bleaching, 500 were severely bleached. Of the 522 reefs surveyed in the more pristine and isolated northern sector (stretching 1000 kms from Port Douglas north to Torres Strait), 81% were severely bleached. Scientists report that: "North of Port Douglas, we’re already measuring an average of close to 50% mortality of bleached corals. At some reefs, the final death toll is likely to exceed 90%. When bleaching is this severe it affects almost all coral species, including old, slow-growing corals that once lost will take decades or longer to return.”
Coral polyps are invertebrates similar to minute jelly fish, which build limestone (calcium carbonate) structures, and live in a symbiotic relationship with algae-like unicellular zooxanthellae that reside within the coral structure, and give it colour.
The US National Oceanic and Atmospheric Administration explains:
The coral provides the algae with a protected environment and compounds they need for photosynthesis. In return, the algae produce oxygen and help the coral to remove wastes. Most importantly, zooxanthellae supply the coral with glucose, glycerol, and amino acids, which are the products of photosynthesis.Corals survive within a narrow water temperature band, and suffer heat stress and expel zooxanthellae if the ocean temperature get too high. Bleaching events vary intensity. In the extreme case, all zooxanthellae are expelled and the living colony will appear totally white (hence "bleaching"). As elevated sea temperatures persist, coral mortality rates increase.
Charlie Veron explains:
Coral mortality means the corals have expelled all zooxanthellae, and starve to death, which may take months. Corals may recover, if there are any zooxanthellae left in their tissues, but if not death appears to be inevitable.Put bluntly, more than half the corals north from Port Douglas have already been identified as dead, and as observations continue over the next few months that figure is likely to rise sharply. Climate change has just killed most corals in the Great Barrier Reef's highest-value section.
Coral expert Prof. Ove Hoegh-Guldberg says that "An increase of as little as 1-2°C on top of regular summer temperatures can mean the difference between life and death for coral reefs."
Previously, the most widespread bleaching events on the GBR occurred in the summers of 1998 and 2002, with 42% and 54% respectively of reefs bleached to some extent, and 18% strongly bleached. However coral losses on the Reef between 1995 and 2009 were largely offset by growth of new corals.
Following bleaching, three developments may occur:
- Corals that have experienced only partial bleaching and not lost all their zooxanthellae are likely to recover.
- Where bleaching has killed a coral, colonies may re-grow from new lava. Denuded reefs that are downstream from reefs which have survived recover quickest. It takes 10-15 years for reefs to look good but that only happens if there is no further bleaching over that time. That is why the frequency of bleaching is so important, somewhat like forests after a fire.
- The other outcome is a regime shift, where previously flourishing coral reefs become diseased and are taken over by thick layers of macroalgae. As just one example, Prof. Terry Hughes tweeted this photo (below) on 2 May 2016: "In 1998, global warming #bleached and killed this mature thicket of Acropora pulchra. Note the recovery since then."
|Bleaching killed this mature thicket of Acropora pulchra|
Half of the world's coral reefs have been lost or are severely threatened from a number of contributing factors: bleaching caused by climate change, invasive species such as the crown-of-thorns starfish, the effects of agricultural nutrient run-off degrading water quantity, and physical destruction from cyclones.
GBR coral populations declined 50.7% between 1985 and 2012. About 10% of the decline was attributable to bleaching. The remaining 90% was caused about equally by tropical cyclones and crown-of-thorns starfishes.
And this is before we start to talk about ocean acidification. Coral's calcium carbonate structures are very vulnerable to increased levels of carbonic acid in the sea, which are a consequence of drawdown of more and more carbon dioxide into the world's oceans. The last time oceans became acidic as fast as they are today, 96% of marine life went extinct, and the Pacific Ocean has already become acidic enough to dissolve sea snails' shells.
Why the bleaching occurred
Surface sea temperatures in the Coral Sea region set a new record in March, at more than 1°C above the recent average (as the chart illustrates), and attributable to climate warming. Scientists estimate that "there is at least a 175 times increase in likelihood of hot March months because of the human influence on the climate."
The global average land and sea surface temperature for February 2016 was 1.6°C, and for March 2016 was 1.53°C, above the 1880-1900 baseline, according to NASA data. The average for January-March 2016 was 1.5°C, being the high point of the 2015-16 El Nino's strong effect on temperature. (El Niños increase global temperatures in the short term; La Niñas have the opposite effect.) By way of comparison, the current trend warming over recent years is around 1°C.
But researchers say the bump in temperatures caused by the El Nino is not the main driver of the warm waters around the reef:
The decaying El Niño event may also have affected the likelihood of bleaching events. However, we found no substantial influence for the Coral Sea region as a whole. Sea surface temperatures in the Coral Sea can be warmer than normal for different reasons, including changes in ocean currents (often related to La Niña events) and increased sunshine duration (generally associated with El Niño conditions). Overall, this means that the influence of El Niño on the Coral Sea as a whole is weak. There have been severe bleaching events in past El Niño, neutral and La Niña years.Future warming and the fate of coral reefs
Whilst March 2016 might seem like an extreme event, the problem is that soon it won't be. Researchers say that:
March 2016 was clearly extreme in the observed weather record, but using climate models we estimate that by 2034 temperature anomalies like March 2016 will be normal (emphasis added).The events of this year could happen every second year in just two decades.
That's hardly surprising. Global average warming is now 1°C and another 0.5°C or more is inevitable over the next few decades (in the absence of geo-engineering) because of our climate "Faustian bargain", so named by Prof. James Hansen.
Here is the dilemma:
- Reducing fossil fuel use and CO2 emissions will also reduce the production of aerosols (soot, organic carbon, sulphates and nitrates, etc) which have a short-term cooling impact. The loss of the aerosol cooling effect will increase the global temperature, in total ~0.5°C or more.
- The present rate of emissions implies warming a per decade of 0.2-0.25°C, so warming is likely 0.6-0.75°C over the next 30 years.
- Cutting CO2 emissions will not decrease the warming of 0.6-0.75° over this period, because reducing the burning of fossil fuels will reduce level of cooling aerosols, hence the "Faustian bargain".
- Reducing CO2 emissions now will decrease warming over the longer term.
We have no carbon budget left for the 1.5°C target and the opportunity for holding to 2°C is rapidly fading unless the world starts cutting emissions hard right now.This is consistent with research on scenarios to hold warming below 1.5°C by 2100, such as this 2015 paper. All published 1.5°C scenarios involve "overshooting" or exceeding the target (rising to around 1.75°C), and then cooling back to the target by 2100, using carbon drawdown technologies. The carbon budget for the 1.5°C scenarios from now till 2100 (with a high 50% risk of failure) is 0−200 billion tonnes of carbon dioxide. That translates to the 1.5°C carbon budget having already expired, or doing so within the next five years.
In summary, the 1.5°C target means we will "overshoot", and that we will have to draw down almost every ton of carbon we emit into the atmosphere from now on.
What is safe for coral reefs?
In 2009, Australian scientists contributed to an important research paper, "Limiting global warming to 2°C is unlikely to save most coral reefs”, which found that:
Preserving (greater than) 10% of coral reefs worldwide would require limiting warming to below 1.5°C (atmosphere–ocean general circulation models, range: 1.3–1.8°C) relative to pre-industrial levels.In fact their 1.5°C boundary has proved to be too high, given that global average warming of 1°C has proved deadly in 2016.
When the climate system is at equilibrium (in a balanced state), 1°C of global average warming is equivalent to atmospheric levels of around 350 parts per million of carbon dioxide (ppm CO2). The present level is now over 400 ppm.
Thus, even 350 ppm is not safe, as Charlie Veron noted in 2009:
The safe level of atmospheric CO2 for coral reefs is ~320 ppm. This identifies a bench-mark level for contemporary marine ecosystems. More than any other available measure, it sets the safe limit for a healthy planet during a time of abrupt greenhouse-driven climate change.With Ove Hoegh-Guldberg, Veron also authored a research paper in 2009, entitled "The coral reef crisis: The critical importance of (less than) 350 ppm CO2", which clearly described the safe zone for coral reefs:
Temperature-induced mass coral bleaching causing mortality on a wide scale started when atmospheric CO2 levels exceeded 320 ppm. When CO2 levels reached 340 ppm, sporadic but highly destructive mass bleaching occurred in most reefs world-wide, often associated with El Niño events… At today’s level of 387 ppm, allowing a lag-time of 10 years for sea temperatures to respond, most reefs world-wide are committed to an irreversible decline.To repeat, at less than today's carbon dioxide level, most reefs world-wide are committed to an "irreversible decline”.
On the 6 July 2009, the Royal Society, the Zoological Society of London and the International Programme on the State of the Ocean facilitated a Coral Reef Crisis meeting to identify key thresholds of atmospheric carbon dioxide needed for coral reefs to remain viable. It concluded that:
To ensure the long‐term viability of coral reefs the atmospheric CO2 level must be reduced significantly below 350 ppm. In addition to major reductions in CO2 emissions, achieving this safe level will require the active removal of CO2 from the atmosphere."What to do?
So 1.5°C of warming will be a death zone for coral reefs, but we already have 1.5°C in the system?
That's too much to bear. Is there an answer? Perhaps.
The only way now to "protect" coral reefs for the long term would be to cool the planet before more deadly bleachings occur, and keep it cool till we can both stop carbon emissions and get carbon dioxide levels down towards the level scientists say is safe: around 320 ppm CO2.
Cooling the planet quickly can be done deliberately, for example, by putting more sulphate aerosols into the upper atmosphere, which is a form of incoming solar radiation management (SRM), or geo-engineering. Physically it can be done, it isn't cost prohibitive and, in coarse terms, it will work.
But…. and it's a big "but"… at the moment such an action is far from being on policymakers' agenda, or the agenda of any government.
One reason is concern that SRM will create a "moral hazard", a temptation by governments to use SRM as a substitute for eliminating carbon emissions and drawing down atmospheric carbon. Whilst SRM can lower the Earth's temperature, it cannot simultaneously restore all features of the climate at a regional level, such as temperature and rain/snow distribution. Some nations and peoples could be significantly worse off. And SRM does not counter dangerous levels of ocean acidification.
Climate modelling shows that using only SRM to control temperature whilst continuing on a high-emissions path leads to very dangerous side effects. (So does a high-emissions path without SRM!) There appears to very little work done on the effect of SRM combined with an emergency program for zero emissions and carbon drawdown, and insufficient work on regional application and impacts.
There are crucial unresolved ethical and governance issues, but we need to need to set aside the reflex taboo that some people have begun to build up around CO2 drawdown or SRM. Most political activists and decision makers find it politically poisonous to consider the use of SRM but, without near-term cooling, the reef's death spiral cannot be halted.
Effective action on climate change has been delayed so long that there are no longer any ideal solutions. We live in a world where our best hope is to aim for least-worst outcomes.
It's one of the many reason we face a "climate emergency", in the words of Prof. Stefan Rahmstorf. It is an emergency because climate impacts now threaten to overrun ecosystems like the Great Barrier Reef, and human societies, and climate policymaking and actions have been so inadequate that we are now going backwards. The gap between what needs to happen and what is being done is getting squeezed into a rapidly disappearing time frame. Society now needs "all hands in deck" and a mode of responding to the climate emergency that maximises the resources and efforts to save our world, including the Reef.
Solar radiation management is problematic, and it should be used only if it is proven to be of net ecological benefit. But, in the end, we cannot "Save the Reef" without it.
If "Saving the Reef" needs carbon dioxide levels of 320ppm or less and some cooling right now to halt the death spiral, shouldn't we say so, no matter how unpopular and difficult? If we aren't prepared to publicly canvass such options, what does the conversation about "saving the Reef" amount to?
Brightsiding is a bad strategy.
Dr Chris McGrath says that:
No one likes to say it out loud, but we should publicly recognise that we are planning to destroy the Great Barrier Reef by setting targets for climate change that we know are inadequate to protect the reef. If we look at the big picture, our lack of serious ambition to protect the reef from climate change will swamp the many good things we are doing to protect it by increasing fully protected areas, reducing fishing pressure, improving water quality, etc.Climate advocacy groups have been using the Great Barrier Reef as a motivator for climate campaigns for many years, but it is hard to identify any science-based, long-term Reef protection plans they have developed that would actually stop the Reef's climate-change-driven death spiral.
In general, climate activists and supporters believed that their actions would "protect the Reef", and many are dazed at the recent bleaching. They should not have been shocked if they understood what the coral experts have been forecasting because as soon as the 2015 El Nino gathered pace and a large warm water blob formed in the Pacific, scientists told us this outcome was on the cards.
And in his 2009 Royal Society presentation, Charlie Veron included a slide (below) which said: "400 (ppm) will be reached by ~2015; will cause major weather events; will cause severe bleaching, mainly during El Nino years". He was spot on. So the science-aware have known for at least seven years that this moment would arrive.
|Slide from Charlie Veron's Royal Society presentation in 2009|