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Isotopes and Environmental Change - Looking Back to the Future

The International Conference on the Study of Environmental Change Using Isotope Techniques concluded 27 April 2001 in Vienna with some 150 experts from 38 countries and 7 international organizations considering state of the art isotope techniques and research in climate change. The conference, the third such held by the Agency, was co-ordinated by the IAEA's Division of Physical and Chemical Sciences (NAPC) and the Marine Environment Laboratory (NAML) in Monaco. The goal of the conference, as noted by Deputy Director General Werner Burkart in his opening address, was to "achieve a critical review of the state of the art and develop a clear vision for the future". This is timely given the ongoing concerns in many quarters over changes in climate and the effect of greenhouse gases on world temperatures.

Predicting future climate is no small challenge. In January, the Intergovernmental Panel on Climate Change raised the ominous spectre of melting polar ice and rising sea levels with its prediction that global temperatures could rise by almost 6oC by 2100. But thankfully, this is a worst-case scenario and the warming trend may actually prove to be much lower than even the minimum prediction of 1.4oC, if governments can be convinced to swing into action collectively to reduce global emissions of greenhouse gases.

Such future predictions are based on complex modeling, whose accuracy depends on the quality of the data on which they are based. This is where isotope techniques come in. Environmental isotopes are one of the most powerful tools to investigate climatic changes and the environmental response to those changes. This is because these isotopes, both stable and radioactive, are preserved in various natural archives such as sediments in lakes and oceans, ice in glaciers or polar ice caps, water in precipitation and oceans, and even trees. The subtle changes in the concentration or type of isotopes can be accurately measured and compared to reconstruct an accurate climate history. This data can also be used to study the complex interactions between the sun, atmosphere, oceans, and biosphere, which together influence climate.

One of the most common uses of isotopes, particularly carbon-14 (14C), is to determine age by measuring the decay products of14C over time and, based on the known decay rate for14C , estimating when the14C would have first been absorbed. This technique, known as radiocarbon dating, is widely used to date fossils and sediments, but can also be used in atmospheric studies, since carbon dioxide is present in large quantities in the earth′s atmosphere. Tracing of14C and elated stable isotopes such as carbon-13 (13C) and oxygen-18 (18O) in atmospheric carbon dioxide can be used to study interactions between oceanic, atmospheric, and terrestial carbon reservoirs over time. Carbon dioxide is also an important greenhouse gas, making the study of its movement over time all the more important to understanding its role in climate change.

Isotopes of hydrogen and oxygen can also be used to date and study the movements of water, since water is made up of these two elements. For example, by comparing the ratio of certain oxygen isotopes in shells found in marine sediments deposited on the ocean floor, it is possible to determine the temperature of the water over time, because the ratio is affected by temperature.

One of the greatest sources of information on past climate comes from studies of polar ice caps and mountain glaciers. In such studies, cores are drilled through the ice down to bedrock. The isotope composition from this ice core can then be determined to estimate such things as temperature, precipitation rate, wind speed, and greenhouse gas concentration over extremely long periods, since the isotopes are frozen in the ice in a virtually timeless record.

Over the course of the weeklong Conference, experts presented the latest results of their research spanning the complete breadth of the field -- studies of oceans and lakes, glaciers and polar ice, paleogroundwater, and precipitation modeling. The proceedings and papers presented at the Conference are expected to be published later this year and will add to the growing body of literature in this important area of research.

Environmental change and climate variability occur on global or continental scales, which is why international collaboration is so vital. The Conference provided an important opportunity for eminent climate change researchers to exchange information and discuss state of the art isotope techniques used in this work. During an afternoon roundtable, participants also discussed the future role of isotopic research in climate change and provided suggestions on possible roles for Agency in this area.

"We certainly appreciate the high regard that was expressed for the Agency's competence and technical expertise", noted Pradeep Aggarwal, who along with Pavel Povinec of NAML acted as co-scientific secretaries of the conference."We will carefully consider and follow up on their suggestions."

The study of environmental isotopes plays an important role in understanding past climate change. It is this understanding of changes in the past that holds the key to predicting future changes --changes that may not only influence global temperatures, but also energy needs, availability of drinking water, and adequate food supplies. So in this sense, isotopes are an invaluable tool to help scientists look back to the future and develop options to minimize the effects of changes to the global climate.

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