HKU Bulletin June 2004 (Vol. 5 No. 4)

5 COVER STORY H ong Kong’s reclamation and other coastal engineering projects have come under considerable f lak for their environmental impacts. But in the study of climate change, they have been an unlikely blessing. Dr Wyss Yim, Associate Professor of the Department of Earth Sciences has ‘piggy-backed’ on coastal engineering projects over the past 30 years to drill into the sea floor to reveal evidence that helps to explain climate change over the past 500,000 years. From the ai rport si te at Chek Lap Kok to High Island Reservoir, he has been able to col lect sediment and other material that shows there have been five cold and five warm per iods over the past hal f mi l l ion years, wi th the cold periods ending rather abruptly. “This research has arisen thanks to al l the coastal engineer ing construct ion in Hong Kong. Because there are so many projects here, I can do my work at a very low cost,” he said D . r Yim’s findings have been suppor ted by inter nat ional researchers, who dr i l led through the Antarct ica ice sheet and reached simi lar conclusions on the frequency of climate change. His research also forms the basis of a display on the subject at the Science Museum’s Science Corner that runs from mid-July until mid-November. “Climate change and sea- level change are closely linked,” he said. “During ice ages, the sea level would drop below present levels by roughly 130 metres, and the existing continental shelf would be exposed. You could walk across Victoria Harbour and that is possibly when Asians migrated to North America. During warm periods, the sea level was roughly as high as the present day.” Temperatures were about 7 – 9ºC colder than today’s mean annual temperature of 24ºC and highland areas commonly saw frost in winter months. But the cold periods would end relatively abruptly, a phenomenon that Dr Yim attributed to the sudden increase in carbon dioxide and methane in the atmosphere. These greenhouse gases formed when marine mud was exposed to air because of lower sea levels, he said. The mud contained pyrite, which formed sulphuric acid on oxidation. The sulphuric acid reacted with marine shells and coral skeletons to produce carbon dioxide. Methane was released from plant matter on the now-exposed sea floor. “Both carbon dioxide and methane trapped in air bubbles in Antarctica ice show a very steep rise at the end of ice ages. The continental shel f is ideal for explaining why this happened because we know it was exposed,” he A s s aid fo . r the formation of ice ages, Milankovitch suggested it may be related to Earth’s orbit of the sun and the fact it moves away f rom the sun every 100,000 years or so, he said. His exhibition – which was selected through a ballot on the Science Museum’s website – will feature evidence from Hong Kong’s ancient past, including a piece of wood more than 130,000 years old that was discovered while dredging for sand of f Cast le Peak. The wood was part of a submerged forest and had a v-shaped cut that may possibly have been made by humans. What Dr Yim’s work cannot explain, however, is the current state of cl imate change. Debate on global warming has heated up recent l y wi th the release of the Hol l ywood mov ie, The Day After Tomorrow , which sensa- t ional i zes the worst-case effects of rapid warming. “There’s a lot of uncertainty over what will happen in future. Based on the last 500,000 years, if there were fewer people in the wor ld we should go back into an ice age. But wi th the unprecedented amounts of greenhouse gases being pumped out through the burning of fossil fuels, nobody knows what is going to happen,” he said. Except, perhaps, that Hong Kong is likely to grow further into the sea. Dr Yim’s research has also helped to provide engineers with better information about the deposits on the sea floor – information they can use when deciding where to put the next reclamation. Climate Change A Walk Across Victoria Harbour 4