Interview Professor Sandy Tudhope
Corals key to understanding climate change…
Interview Professor Sandy Tudhope
Corals Key to understanding climate change
It may be a long way from Scotland, and a few degrees warmer, but scuba diving in the South Pacific may help Sandy Tudhope and his international colleagues change our attitudes to climate change – by measuring the growth of one of nature's most sensitive and beautiful organisms...
Professor Sandy Tudhope has spent a lot of his career underwater, but he also believes that immersing himself in the societies where he does field work has had a major influence on how he thinks about science, including his specialist subject – the study of coral.
Born and educated in Scotland’s capital city, Tudhope is today the Head of School of GeoSciences at the University of Edinburgh, but even though he has spent many years close to home, he regularly travels to some of the world’s most exotic locations. He started scuba diving in the northwest of Scotland while studying geology in Edinburgh, focusing on the environmental significance of carbonate sediments or shell sands. After graduation, he went to the Australian Institute of Marine Science in Townsville to do his PhD, researching the processes which control the growth and development of the Great Barrier Reef. For three years, Tudhope found himself surrounded by scientists of every description, including oceanographers, biologists and chemists, focusing on marine science rather than traditional geology, and this emphasis on multidisciplinary teamwork has been a major influence in his career.
As a Professor of Climate Studies working with people from all sorts of backgrounds, Tudhope is well aware his scientific discipline is also closely intertwined with economic, social and political considerations. “It’s important to put things in context,” he says. “Because of rising sea levels, the future does not look good for some people in the Pacific and elsewhere.” Faced with the reality of people whose environment is threatened by the fall-out from societies thousands of miles from their homes, scientists not only see how critical their work is but may also ask different questions because of this different perspective.
The basic question scientists ask about coral is: “Why does it look like this?” In other words, how does it form its skeleton of lime and what controls its growth? But Tudhope and his colleagues also flip the question over to ask what coral tells us regarding the climate. And the answer is not always very good news.
One of Tudhope’s major projects is a study of the coral reefs in Thailand, and this has led to “sobering” conclusions, including the discovery that the growth rate of the coral has slowed down by 15 per cent in the last 25 years – a finding confirmed by a similar study of coral in the Great Barrier Reef in Australia. “We know we are both right concerning the figures,” says Tudhope, “but it's harder to say why it's happened.”
Tudhope has spent lots of time in Australia and the rest of the Pacific Ocean area, including the Galapagos and Papua New Guinea, where he studied living corals and fossilised corals at the same time in the same environment, using the fossils to understand climate change dating back thousands of years, spanning interglacial-glacial cycles. In Papua New Guinea, the land is rising out of the ocean, resulting in the exposure of former coral reefs. By studying these fossilised corals it is possible to step back in time – the higher the fossils, the older they are – and to use the evidence within the coral skeletons to reconstruct past climate change.
“Papua New Guinea is the perfect laboratory,” Tudhope explains, but to get the big picture, it’s important to travel around the whole area, gathering data from different locations, including some where scientists have never before done research into corals. In some places, temperature is the critical factor, while in other places rainfall or ocean-acidification has more impact than anything else.
The scientific study of coral reefs in the Pacific can be traced back to the work of Charles Darwin in the early 1830s, which eventually led to the publication of his first monograph in 1842, The Structure and Distribution of Coral Reefs. Darwin’s theory was that the shape and structure of coral reefs (such as atolls, barrier reefs and fringing reefs) reflected the combined effects of uplift or subsidence of the Earth’s surface, and the ability of coral reefs to grow upwards and outwards. “Darwin was acutely aware of changes in sea levels,” says Tudhope, but it was many years before we started studying the coral reefs for evidence of climate change, extracting data on temperature, sea levels and salinity.
Geologists have known about the evidence of climate change in sedimentary rocks since the earliest days of the science, but this referred to long-term geological time-scales and it was not until more recent years that scientists started to apply very similar principles to the study of coral, to understand what’s happened to the living organism in the short term. Some reef-building corals lay down massive lime skeletons that have annual bands, similar to tree rings, says Tudhope, and they record in the structure and chemical composition of their skeletons, information about the temperature and salinity of the surrounding seawater. These attributes, combined with the longevity (up to several centuries) and fast growth rates (10–20mm/year) of some coral colonies make them ideal archives of information on past climate variability and change.
The effects of climate change on corals can be highly complex and not always easy to measure. For example, rises in water temperature do not always have the same effects. Coral generally thrives in warm water – growing faster as the temperature rises. But when the temperature reaches a critical level, the coral starts to bleach and die. In some places, such as the Persian Gulf, coral thrives in temperatures of 34 degrees centigrade, while the same type of coral in other places, such as the Great Barrier Reef, where the water is five degrees cooler, would die at these temperatures. This variability in optimum temperatures means that research has to cover a very wide area, taking account of both temporal and spatial factors.
Another big danger to coral is acidification caused by excess carbon dioxide dissolving in water, which makes it much harder for the coral to form its lime skeleton. Combined with rising temperatures, this can spell catastrophe for coral. But there is also growing evidence that coral can adapt and acclimatise over time, developing defences to cope with these changing conditions.
In addition, says Tudhope, the biggest threats to coral are much more direct – over-fishing, dynamiting and pollution caused by sewage and agricultural effluence, washing excess nutrients into the sea which encourage the growth of the algae which out-compete coral. In recent years, scientists have also observed that corals are becoming more prone to disease, but the jury is still out regarding the causes.
Over the course of Tudhope’s career, new technologies (including mass spectrometers which analyse the chemistry) have revolutionised the work of palaeoclimate scientists, greatly improving precision and making it possible to analyse very small sample sizes (extracted from the core of the coral) more quickly than ever before. These advances allow the routine reconstruction of many centuries of past climate at monthly resolution at different sites around the tropical oceans. But for Tudhope, the biggest change is how different scientists work with each other in ways that blur the boundaries between the different disciplines.
“The big advance has been the willingness of scientists from very different backgrounds – like biology and chemistry, geology and physics – to engage with each other,” says Tudhope. “Geologists have traditionally used their observations of rocks to create a narrative of changing environments through time. Now the challenge is to work with scientists from other disciplines to learn from one another – for example, using physics to help constrain what is possible and what is impossible in terms of apparent changes in past climate, and to understand the strengths and weaknesses of different natural archives for reconstructing the nature and timing of past changes. My academic papers reflect collaborations with scientists from all sorts of backgrounds.”
In some ways, says Tudhope, this means we have come full circle since Darwin’s time, when scientists did not define themselves so rigidly and tended to explore a range of disciplines. Scientists today may not be individual “all-rounders” like Darwin, but the team they are part of can behave in a similar way – communities of scientists combining their specialist skills. Definitions are no longer so important, says Tudhope, and degree subjects should not put scientists into a box for the rest of their lives.
Another major change in climate science over the last 50 years has been the realisation that people have become the biggest agent of change on the planet, and this has also changed the questions scientists ask when they try to disentangle human influence from natural variability, as well as how the different disciplines contribute to the sum of our knowledge. “Society wants answers,” says Tudhope, “but no single discipline can come up with all of the answers.”
Another major area of interest for Tudhope is the El Niño Southern Oscillation, or ENSO. This climatic phenomenon, which causes extremes in temperatures, floods, droughts and cyclones across the Pacific on a 2–5-year cycle, has only really been understood for the last 30 years. Even now, says Tudhope, the physics only gives us a general picture, and we still have many unanswered questions about the sensitivities of ENSO to changes in climate. For example, is it possible to predict the likelihood of a particularly strong event? “El Niño is the single biggest source of year-to-year climate variability on Earth,” says Tudhope, “so it has huge repercussions for societies and ecosystems globally.”For example, droughts in the southwest USA and Mexico, droughts in parts of Southern Africa, failed Indian Monsoon rains, and changed frequencies of Atlantic and Pacific Ocean cyclones and associated flooding are all associated with changes in the ENSO cycle. Instrumental records of ENSO and climate over recent decades, or even the last 100 years, are simply not long enough to reveal the full range of natural variability in this key element of the climate system. Furthermore, due to the complexity of the ENSO system, it is proving to be extremely hard to predict its response to current and future climate warming.
Despite the inherent uncertainty of climate studies, Tudhope is clear about the fundamentals: “It is easy to overstate how little we know. But we are confident the world has warmed and will get warmer, and over the last few decades we have developed climate models which can simulate well the global climate system.”
There are about 10–15 “reasonably good climate models,” says Tudhope, “and they tend to agree.” They are better at predicting the average climate, however, than the local or regional climate, and the best way to test them is to run them in reverse to see if they confirm the known results. “The aim is to predict the likelihood of major climate changes,” he explains, and this should help develop better policies to cope with events, much the same as insurance firms working out risks. “Climate change is having a major effect on the world and this societal relevance makes it important for scientists to engage with the general public as well as government.”
Tudhope’s pioneering work with corals does not just help us understand why they grow into such beautiful structures, but also why they set off alarm bells when it comes to the climate. In future, he would like to see more research into the Earth’s hydrological cycle – the way that water circulates. Current climate predictions indicate that, where it is currently dry, it will get drier, and where it is currently wet, it will get wetter, but it would be useful to know more about where and when this will happen. The challenge is to understand the interactive systems of the Earth – to understand what happens when the different components of nature collide.