This description of the Great Barrier Reef, obtained by Guardian Australia, was written by experts for a Unesco report on tourism and climate change but removed after objections from the Australian government. This draft would have been subject to minor amendments after being peer-reviewed. The lead author, Adam Markham, is deputy director of climate and energy at the Union of Concerned Scientists.

Significance: World’s largest coral reef system; marine biodiversity; evolutionary processes; spectacular underwater landscapes.

Climate change is the primary long-term threat to the integrity and biodiversity of the world’s most extensive coral reef ecosystem. The Great Barrier Reef (GBR) was added to the world heritage list in 1981. It is one of the world’s most complex and diverse ecosystems, with at least 400 species of hard coral, 150 species of soft corals and sea fans, and more than 2,900 individual reefs and some of the most important seagrass meadows in the world – teeming with marine life of all sorts, including more than 1,600 fish species, seabirds, seahorses, whales, dolphins, crocodiles, dugongs and endangered green turtles. The GBR extends for 2,300km along the coast of Queensland in Northeast Australia and has evolved over a period of 15,000 years (Great Barrier Reef Marine Park Authority 2012, Unesco). The GBR region is important for the indigenous heritage of First Australians - Aboriginal and Torres Straits Islander people - who are the traditional wners. Climate change threatens hunting and fishing as well as other traditional and cultural practices. Some sacred sites are also at risk for the more than 70 traditional owner groups for whom natural resources are inseparable from cultural identity (Great Barrier Reef Marine Park Authority 2012).



Rising sea temperatures, accelerating rates of sea level rise, changing weather patterns and ocean acidification

Louis de Bougainville was probably the first European to sight the GBR in 1768 and Captain Cook was the first to try to navigate the reefs in 1770 and it was the reports of Cook and naturalist Joseph Banks on their return to England that first alerted the scientific world to the existence of this marvel. Captain William Bligh too survived the reef after being cast into a small boat after a mutiny on his ship HMS Bounty in 1789. Bligh and his companions survived a remarkable journey sailing thousands of kilometers to safety in Timor after being cast adrift, finding their way into the GBR at what is still known as Bligh Boat Entrance and out at Restoration Island.



The GBR is now one of the world’s most important coastal and marine tourism areas. A few tourists were visiting the reef as early as the 1890s but modern tourism was very minor before the 1950s and only really took off in the 1960s and ‘70s. Today, tourism (including touring, diving, beaches, sailing, fishing and cruising) is the most important economic sector in the GBR communities, contributing $5.2bn dollars to the Australian economy in 2012 and supporting 64,000 jobs, or about 90% of the total economic activity in the region (Deloitte Access Economics 2013). Visitors spent nearly 43m total nights in the GBR region in 2012, of which nearly 2m nights were on the reef, mainly at Cairns and the Whitsunday Islands (Deloitte Access Economics 2013). Direct reef-related tourism alone contributes 4,800 jobs. Approximately 500 commercial boats operate bringing tourists out to dive and snorkel on the reef and there can be negative impacts associated with this, including damage from fuel spills and walking and dropping anchors on fragile corals. Tourism infrastructure, along with other coastal developments, can cause habitat degradation and damaging pollution and sediment run-off.



The biggest long-term threat to the GBR today, and to its ecosystems services, biodiversity, heritage values and tourism economy is climate change, including rising sea temperatures, accelerating rates of sea level rise, changing weather patterns and ocean acidification. (Great Barrier Reef Marine Park Authority 2012). Coral reefs worldwide are being directly impacted by warming waters and ocean acidification and climate change is exacerbating other localized stresses (Hoegh-Guldberg et al 2007). Ocean acidification is occurring because of increased levels of carbon dioxide in the atmosphere. A significant portion (about 25-30%) of this CO2 is being absorbed by the oceans and the resulting increases in seawater acidity reduces the capacity of some marine life, such as corals, to build their calcium carbonate based skeletons. Significant drops in coral growth rate have been recorded in the last two decades for massive Porites corals on the Great Barrier Reef.



Coral bleaching seen at Loomis Reef, off Lizard Island, Great Barrier Reef, Australia. Photograph: Essential Media

Other significant threats include coastal development, agricultural run-off pollution, port-based shipping activities, illegal fishing and outbreaks of the coral-eating crown-of-thorns starfish. Assailed by multiple threats, the GBR has been assessed as being poor and deteriorating. Half of its coral cover has been lost over the last three decades. Unusually high sea temperatures have caused eight mass coral bleaching events on the GBR since 1979, with the worst occurring in 1998 and 2002 (Great Barrier Reef Marine Park Authority 2012, Steffen et al 2009, Hughes et al 2015). Coral bleaching occurs when higher than usual maximum temperatures disrupt the relationship between corals and the photosynthetic zooxanthelae algae that live in their tissues in a vital and mutually beneficial biological relationship. Bleaching can kill corals, but depending on the severity of the impact and local factors they can also recover. The same is true for coral damage from storms, but damaged or bleached corals and reefs need time to do so. All indications are that bleaching events will become more frequent and tropical storms more intense with continued global warming, and that this combined with a continued trend in warming water and ocean acidification will be massively detrimental to the GBR (Hoegh-Guldberg et al 2007, Steffen et al 2009, Great Barrier Reef Marine Park Authority 2012).



Without global efforts to reduce greenhouse gas emissions coupled with local management responses to increase resilience, current projections suggest that coral cover could decline to 5-10% of the GBR by the early 2020s from 28% in 1985 – a potential loss of 80% in just 40 years (De’ath et al 2012). Similar fears are associated with one of the other keystone ecosystems of the GBR, seagrass meadows representing 20% of the world’s 72 seagrass species. These shallow-water habitats provide vital nursery areas for fish and shrimps, critical food resources for turtles and dugongs and act as carbon sinks, sequestering organic carbon in marine sediments. The combination of agricultural runoff, fishery impacts and climate change may exceed seagrass beds’ natural ability to adapt (Coles et al 2014). Sea turtles too are at risk from climate change as high temperatures and sea level rise impact their breeding and nesting beaches (Great Barrier Reef Marine Park Authority 2012).



Concern has continued to grow that … [the reef's] biodiversity and natural beauty may lose its World Heritage values

Spurred by the direct evidence of climate change already impacting the GBR, degradation of the reefs and the likelihood of much worse to come, the Australian government has begun to plan and implement actions to reduce the risk of future damage. At the core of the adaptation strategy are efforts to build ecosystem resilience, fill gaps in scientific knowledge, and monitor environmental, social and economic impacts of climate change (Great Barrier Reef Marine Park Authority 2012). Collaborative management strategies are also being developed and tested with local communities, Traditional Owners, as well as with business and industry. The GBR was also the first World Heritage property for which a comprehensive Tourism and Climate Change Action Strategy was developed (Great Barrier Reef Marine Park Authority 2009). The strategy recognizes the vital importance that a healthy GBR ecosystem plays for the Australian economy and that the tourism industry must quickly come to grips with the problem. Recommended actions include reducing direct impacts and greenhouse gas emissions from tourism companies operating on or near the reef; increased training and awareness for guides and operators; helping to raise public understanding of the threat, and; supporting scientific research and monitoring activities (Great Barrier Reef Marine Park Authority 2009). The plan also calls for the industry itself to plan adaptive responses for declining reef conditions and to contribute to risk management strategies for climate disasters.



Despite these measures, international concern has continued to grow, however, that without a comprehensive response more in keeping with the scale of the threat, the GBR’s extraordinary biodiversity and natural beauty may lose its World Heritage values. IUCN’s World Conservation Outlook 2014 assessed the status of the World Heritage values of the GBR as of “high concern” and experiencing a deteriorating trend (IUCN 2014). The most recent strategy from the Australian government, the Reef 2050 Long-term Sustainability plan, addresses this issue head on and is specifically designed to “ensure the Great Barrier Reef continues to improve on its Outstanding Universal Value every decade between now and 2050 to be a natural wonder for each successive generation to come” (Commonwealth of Australia 2015).