Feed aggregator

A fifth of the Great Barrier Reef’s corals are dead after the worst bleaching event on record. Most of these deaths occurred in the northern part of the reef above Lizard Island.

Months after the bleaching event, research teams are now taking stock of the damage. Corals can recover from bleaching. But in a changing world they will have less time to do so before the next event.

Bleaching 101

Reef-building corals are animals that live symbiotically with one-celled algae (a species of dinoflagellate known as Symbiodinium, or colloquially as zooxanthellae).

The coral host provides safe habitat within its cells and supplies nutrients, while the algae in return feeds the coral with products from photosynthesis. This partnership is highly efficient. It allows stony corals that require a lot of energy to produce their skeletons to thrive in nutrient-poor tropical waters. But it is also a fragile balance.

Environmental stress, most commonly caused by increased water temperatures and elevated light conditions, can cause the zooxanthellae to produce too much reactive oxygen species, which is toxic to the coral. So the coral expels the algae.

This is what is actually happening when a coral “bleaches”. Expelling 90% or more of the algae, the coral’s skeleton becomes visible through its tissues.

A bleached coral can stay alive but is deprived of its primary food source and will begin to starve. Its metabolism suffers, the immune system becomes compromised, it becomes more susceptible to disease, and defence against coral predators, such as snails known as Drupella, is weakened.

Survivors of the bleaching are suffering from increased predation pressure. Drupella snails aggregate on the remaining live corals around Lizard Island following the 2016 bleaching event. Greg Torda

Depending on the intensity and duration of environmental stress, corals can die from the immediate impacts of a severe heat stress; starvation; disease or being eaten.

If conditions get better, corals can regain their symbiotic algae – and with it their brownish colour - from the surrounding water or from the multiplication of the remnant algae within their cells. In this way individual coral colonies can recover.

Corals weakened by heat stress are more susceptible to coral diseases. Here, skeletal eroding band disease is slowly killing a Pocillopora colony in the aftermath of the 2016 bleaching event. Greg Torda

Different coral species bleach at different stress levels, and some species are more likely to die directly from the conditions that cause bleaching.

For example, the fastest-growing corals are highly effective at capturing light to feed their algal fuel cells. Even under normal conditions they are living close to their maximum tolerance of temperature and light. These corals are far more susceptible to more light and temperature than other, slower growing corals.

Incidentally, these fast-growing corals are also the ones that provide the bulk of the intricate three-dimensional structure to the reef that is critical to most reef critters, including fish. Because of their enhanced metabolism, fast-growing corals also die in greatest numbers during bleaching events, therefore they have been considered the losers of coral bleaching.

Field of recently dead staghorn corals. These corals still provide habitat for some reef critters, but will soon erode to rubble. Greg Torda Reef recovery

Due to the variability in bleaching and coral deaths, even moderate bleaching events can decrease the amount of live coral on the reef’s structure and can dramatically alter the species composition.

The recovery of the reef after a disturbance, such as a bleaching event, happens when the amount of live coral covering the reef, the structural complexity, and the composition of the coral community all return to the levels prior to disturbance.

This requires the re-colonisation of the reef by coral propagules (larvae or fragments) that grow into large mature colonies over the course of years and decades.

In severe bleaching events, such as the most recent 2016 mass bleaching event on the Great Barrier Reef and in parts of the remote Pacific Ocean, even the more thermally-tolerant, slow-growing corals severely bleached; several locations suffered large numbers of coral deaths.

The loss of slow growing corals is particularly alarming, because replacing these colonies will require decades, and in some cases centuries, to return the reefs to what they were just a short time ago.

It is unlikely that the reefs affected by the 2016 event in the northern Great Barrier Reef will recover for many decades.

Other symbiotic organisms such as this anemone can also bleach when stressed. Greg Torda Will there be a next time?

It is highly unlikely that reefs will get the decades they need to recover – in fact, the frequency of bleaching events is increasing.

Current trends in ocean temperature and future predictions suggest bleaching will occur each year within the coming decades. Some reefs around the world have just experienced consecutive years of bleaching, with barely any opportunity for colonies, let alone reefs, to recover.

Can corals adapt or acclimatise to elevated water temperatures over the course of a few years? Corals inhabiting unusually warm waters, such as the Persian Gulf and some areas of the Coral Triangle, demonstrate that long-term adaptation to a high temperature regime has been possible.

However, evidence to date suggests that these adaptive processes are unlikely to be able to keep up with climate change.

Action to reduce atmospheric CO2 levels, and halt the associated warming, must be quickly and vigorously pursued to avert the predicted degradation of coral reefs. If this is not undertaken, the consequences for reefs will only be amplified from what we have seen this year.

Tracy Ainsworth receives funding from The Australian Research Council Discovery Program and the ARC Center of Excellence for Coral Reef Studies.

Greg Torda receives funding from the Australian Research Council. He is also affiliated with the Australian Institute of Marine Science.

Scott Heron receives funding from the U.S. National Oceanic and Atmospheric Administration's Satellites division (NESDIS) and Coral Reef Conservation Program, and is affiliated with James Cook University. The contents in this piece are solely the opinions of the authors and do not constitute a statement of policy, decision or position on behalf of NOAA or the U.S. Government.

Campaigners believe a long-standing proposal to establish a vast marine protected area (MPA) in the waters around Antarctica will be accepted this week.

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The analysis, the most comprehensive to date, indicates that animal populations plummeted by 58% between 1970 and 2012, with losses on track to reach 67% by 2020. Researchers from WWF and the Zoological Society of London compiled the report from scientific data and found that the destruction of wild habitats, hunting and pollution were to blame.

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Western Australia could become a renewable energy superpower – if the government halts LNG expansion plans and creates an innovation fund

Last year the world’s governments finally got their act together on climate change, agreeing to limit global warming to well under two degrees. To meet this commitment, we need a rapid global transition to net zero greenhouse gas emissions. The fossil fuel age is over.

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Global wildlife populations have fallen by 58% since 1970, according to a biodiversity report.

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Citizens of the Great Barrier Reef must accept that climate change is damaging the reef, say Climate Council chief and university expert

Scientists and conservationists have called for a purportedly pro-environmental group supporting the Great Barrier Reef to distance itself from climate deniers, after the broadcaster Alan Jones launched the group and said the reef was “fine” and that climate change was a “hoax”.

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As the oceans and atmosphere warm, Australia is experiencing more extreme hot days and more severe fire seasons, according to the 2016 State of the Climate report.

Australia's oceans are heating up. Richard Rydge/Flickr, CC BY-NC-ND

The Australian Bureau of Meteorology and CSIRO have released their fourth biennial State of the Climate Report.

State of the Climate 2016 provides an update on the changes and long-term trends in Australia’s climate. The report’s observations are based on the extensive climate monitoring capability and programs of CSIRO and the Bureau, which provide a detailed picture of variability and trends in Australia’s marine and terrestrial climates. The science underpinning State of the Climate informs impact assessment and planning across all sectors of the economy and the environment.

One of the report’s key observations is carbon dioxide concentrations in the atmosphere. A key component of global CO₂ monitoring is the joint Bureau and CSIRO atmospheric monitoring station in Cape Grim, Tasmania, one of three premier global baseline monitoring stations in the world, along with Mauna Loa in Hawaii and Alert in Nunavut, Canada.

CO₂ concentrations at Cape Grim passed through 400 parts per million for the first time in May 2016, and global concentrations are now at their highest levels in the past two million years.

It takes time for the climate system to warm in response to increases in greenhouse gases, and the historical emissions over the past century have locked in some warming over the next two decades, regardless of any changes we might make to global emissions in that period. Current and future global emissions will, however, make a difference to the rate and degree of climate change in the second half of the 21st century.

State of the Climate focuses on current climate trends that are likely to continue into the near future. This acknowledges that climate change is happening now, and that we will be required to adapt to changes during the next 30 years.

While natural variability continues to play a large role in Australia’s climate, some long-term trends are apparent. The terrestrial climate has warmed by around 1℃ since 1910, with an accompanying increase in the duration, frequency and intensity of extreme heat events across large parts of Australia. There has been an increase in extreme fire weather, and a lengthening of the fire season in most fire-prone regions since the 1970s.

Annual mean temperature changes across Australia since 1910. State of the Climate 2016 Trends from 1974 to 2015 in annual 90th percentile of daily Forest Fire Danger Index (FFDI) at 38 climate reference locations. Trends are in FFDI points per decade and larger circles represent larger trends. Filled circles represent statistically significant trends. Trends are upward (in red), except for Brisbane airport (in blue). State of the Climate 2016

Observations also show that atmospheric circulation changes in the Southern Hemisphere have led to an average reduction in rainfall across parts of southern Australia.

In particular, May–July rainfall has reduced by around 19% since 1970 in the southwest of Australia. There has been a decline of around 11% since the mid-1990s in April–October rainfall in the continental southeast. Southeast Australia has had below-average rainfall in 16 of the April–October periods since 1997.

Australia’s oceans have also warmed, with sea surface temperature increases closely matching those experienced on land. This warming affects both the marine environment and Australia’s terrestrial climate, due to the large influence of surrounding oceans on our weather systems. Sea levels have risen around Australia, which has the potential to amplify the effects of high tides and storm surges.

Trends in sea surface temperature in the Australian region from 1950 to 2015. State of the Climate 2016 Estimates of the change in ocean heat content over the full ocean depth, from 1960 to present. Shading provides an indication of the confidence range of the estimate. State of the Climate 2016

The report has new findings compared to State of the Climate 2014.

Significantly, we report that warming in the global oceans now extends to at least 2,000 metres below the surface. These observations are made possible by the Argo array of global floats that has been monitoring ocean temperatures over the past decade. When we talk about the climate system continuing to warm in response to historical greenhouse gas emissions, that is almost entirely due to ongoing ocean warming, which these observations show is now steadily in train.

The other new inclusion is the science of extreme event attribution.

In the past five years, an increasing number of studies, using both statistical and modelling techniques, have quantified the role of global warming in individual extreme events. This complements previous science which partly attributes a change in the frequency of extreme weather, such as an increase in the number of heatwaves, to global warming.

In Australia, this includes studies that used the Bureau’s Predictive Ocean Atmosphere Model for Australia (POAMA) to essentially predict observed extreme events in a modelled climate with and without an enhanced greenhouse effect.

In particular, studies of record heat experienced during Spring in 2013 and 2014 have shown that the observed high temperatures received an extra contribution from background global warming.

These studies are an initial step towards understanding how climate change could affect the dynamics of the climate and weather system. In turn, this work provides greater intelligence for those managing climate risks.

State of the Climate 2016 can be read on either the Bureau or CSIRO‘s websites. The online report includes an extensive list of references and useful links.

Watch the State of the Climate 2016 summary video.

CSIRO, the Bureau of Meteorology and the Department of the Environment and Energy have provided a comprehensive portal for climate projection science, data and information called Climate Change in Australia. This website includes regional climate projections, a publication library, guidance material and a range of interactive tools.

Karl Braganza is the manager of the Climate Monitoring Section in the Bureau of Meteorology's Environment and Research Division. The Bureau of Meteorology provides Australians with environmental intelligence for their safety, sustainability, well-being and prosperity. Our weather, climate and water services include observations, alerts, warnings and forecasts for extreme events.

Steve Rintoul works for CSIRO. He receives funding from the Australian Climate Change Science Program and the Antarctic Climate and Ecosystems Cooperative Research Centre.

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This symbolic threshold (Carbon dioxide levels bring climate change into a ‘new era’, 25 October) is one of many very real tipping points the world will experience on a path of climate change due to human effects. The tipping points we should also be paying attention to are the mass extinctions, global warming, melting ice and complete habitat changes we are currently seeing worldwide. Soon we will recognise these not as symbolic thresholds but more as points of no return. The Paris and Kigali agreements are both important for slowing down the climate trend wiping out animal and plant species worldwide. But both are just bandages to the real problem of resource management and consumption practices exacerbating the problems to unsustainable limits.
Caroline Hernandez
Chevy Chase, Maryland, USA

• Join the debate – email guardian.letters@theguardian.com

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Ray Chalker
London

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Countries including US, Europe, Australia vehemently oppose small hunts by coastal communities but Japan says are unjustly barred from a traditional food source

Japan pleaded with the world’s whaling watchdog Wednesday to allow small hunts by coastal communities, arguing that for three decades these groups had been unjustly barred from a traditional source of food.

The issue of “small type coastal hunting” is a key dispute between pro- and anti-whaling nations gathered in Slovenia for the 66th meeting of the International Whaling Commission (IWC).

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Government claims oil extraction is causing minimal disturbance to the Unesco biosphere reserve in the Amazon

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But the government claims that there has been only minimal disturbance to the Unesco biosphere reserve in the Amazon rainforest since extraction of 23,000 barrels of oil a day began last month.

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State of the Climate report from CSIRO and Bureau of Meteorology says human activities have driven ‘significant changes’ to Australia’s climate

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