Is it too late to help coral reefs survive climate change?

Is it too late to help coral reefs survive the impacts of climate change? Q & A with Earthwatch scientist Professor James Crabbe

Professor James Crabbe's Earthwatch-supported research in Jamaica and on the Belize barrier reef addressed the impact on coral reefs of climate-driven bleaching and storm events.

Professor Crabbe's latest paper, Modelling effects of geoengineering options in response to climate change and global warming: Implications for coral reefs was published in December, as world leaders gathered at the United Nations Climate Change Conference in Copenhagen. Here Professor Crabbe of the University of Bedfordshire (UK), discusses his latest findings and the future for coral reefs.

How long have you been researching coral reefs and what changes have you witnessed during that time?

Since 2000, when I first went to work on the fringing reefs around Discovery Bay in Jamaica. I then went to work on reefs in Indonesia, and later on with the second largest Barrier Reef in the world, off the coast of Belize in Central America. During this time the reefs have been hit by many impacts, such as bomb fishing and coral mining in Indonesia to hurricanes and mass bleaching in the Caribbean. Despite these human impacts and environmental and climate-induced stressors, some of the reefs I work on in Jamaica have shown resilience, for example coming back after the mass bleaching event of 2005.

Why are coral reefs so important?

Coral reefs, found predominantly between the Tropics of Capricorn and Cancer, provide an environment in which one-third of all known marine fish species and many thousands of other species are found, and from which 6 million tons of fish are caught annually.¹

This not only provides an income to national and international fishing fleets, but also for local communities, which rely on their fish stocks for commercial purposes and nutritional sustenance. Coral reefs also act as barriers to wave action and storms by reducing the incident wave energy through wave reflection, dissipation and shoaling, protecting the land and an estimated half a billion people who live within 100 km of reefs. Coral reef systems form part of a seascape that includes land-based ecosystems such as mangroves, and ideally should form a complete system for conservation and management.

What are the most pressing threats to coral reefs and how is climate change affecting them?

Current challenges to coral reef sustainability include overfishing, destructive fishing practices, coral bleaching, ocean acidification, sea-level rise, crown-of-thorns starfish outbreaks in the Indo-Pacific regions, algal blooms, agricultural run-off, coastal and resort development, marine pollution, increasing prevalence of coral disease, invasive species and hurricane/cyclone damage. These act synergistically on the reefs, and the rapid pace of climate change makes the threats all the more potent.

Why did you write this paper about geoengineering options?

I was one of 23 scientists from around the world invited to a meeting at the Royal Society this summer to produce a statement for Copenhagen arguing for a reduction in carbon dioxide levels below 350 ppm. That statement has been signed by many scientists. At that meeting it was clear to me that such a reduction was not realistic in the time scale - an increase of 2 degrees C will cause most of our reefs to disappear. I therefore looked at geoengineering options for the active removal of carbon dioxide, and how they would influence coral reefs.

What do these various geoengineering options involve?

There are two categories of geoengineering solution to climate change - shortwave solar radiation management and longwave carbon dioxide removal. The first set of techniques only reduce some, but not all, effects of climate change, while possibly creating other problems. They also do not affect CO₂ levels and therefore fail to address the wider effects of rising CO₂, including ocean acidification, important for coral reefs. Solar radiation is important to coral growth and survival (they need the sun for their symbiotic algae to photosynthesize), and solar radiation management is not in general appropriate for this ecosystem.

Longwave carbon dioxide removal techniques address the root cause of climate change, rising CO₂ concentrations, and they have relatively low uncertainties and risks. They are worthy of further research and potential implementation, particularly carbon capture and storage, biochar, and afforestation (creating forests on lands that had not previously been forested) methods, alongside increased mitigation of atmospheric CO₂ concentrations.

How effective could these options be in preventing further damage to coral reefs or is it simply a question of too little too late?

Difficult to say. The safest options, like afforestation and carbon capture and storage, will take time to develop and to work. I would not advocate short wave options, limiting solar radiation to the earth. They won't reduce greenhouse gases or stop ocean acidification, and they have lots of governance problems.

You agree that we are now witnessing the demise of coral reefs. It's not something that will happen because it is happening, and has happened in certain areas....Can you further place into context your paper addressing the geoengineering solutions out there, when it seems it's too late?

It is clear that climate change will continue to alter many aspects of what we know as coral reefs; what is less clear is exactly what the results will be. Coral reefs are disturbance-adapted ecosystems. But what happens when complex processes - e.g. climate change - take a hand?

It appears unlikely that all corals or their symbiotic algae can evolve to keep pace; the rates of change and the numbers of stressors are too great. There will be coral mortality and species loss, coupled with some movement of coral ecosystems in a northerly direction in certain parts of the globe. The reefs off the islands of Bermuda in the Atlantic Ocean - the most northerly in the world - have evolved to produce reefs with little species diversity, but excellent fitness for purpose to cope with the conditions of relatively large fluctuations of temperature throughout the year. If a sufficient number of coral species survive the next 50-100 years, and there is a return to a more steady-state climate environment, coupled with fewer anthropogenic stressors, then coral reef assemblages may gradually recover. My geoengineering review looks at ways in which we can return safely to a more steady-state climate without ecosystem destruction and in combination with mitigation of carbon dioxide emissions.

¹ Cesar, H. 1996. Economic analysis of coral reefs. World Bank, Washington DC; Cesar, H, Lundin, C., Bettencourt, S., & Dixon, J. 1997. Indonesian coral reefs: An economic analysis of a precious but threatened resource. Ambio 26(6):345-350].