Scientists analysed the isotopic composition of water molecules in ice cores from Antarctica and Greenland, using the ratios of oxygen-18 to oxygen-16 and deuterium to hydrogen as proxies for past temperatures. For example, analysis of ice cores from the Vostok station in Antarctica has revealed detailed records of past temperature variations over hundreds of thousands of years, showing the natural variability of climate and the unprecedented rate of recent warming. Similarly, Greenland ice cores have provided high-resolution records of past climate changes in the Northern Hemisphere, showing rapid shifts in temperature during past glacial and interglacial periods.
Dendroclimatology, the study of tree rings, utilises isotopic analysis to reconstruct past climate conditions, with the ratios of stable isotopes, such as carbon-13 and oxygen-18, in tree rings reflecting changes in temperature and precipitation. Studies in regions like the Andes and the Himalayas have used tree ring isotopic data to reconstruct past drought patterns and to understand the impact of climate variability on forest ecosystems. Ocean sediment cores contain the remains of marine organisms, such as foraminifera, whose shells incorporate isotopes from the surrounding seawater, allowing scientists to reconstruct past ocean temperatures, salinity, and circulation patterns. Studies of ocean sediments in the Pacific and Atlantic Oceans have revealed evidence of past changes in ocean circulation, such as the El Niño-Southern Oscillation and the Atlantic Meridional Overturning Circulation, and their impact on global climate. Stalagmites, found in caves, also hold climatic information, with the Oxygen isotope ratios found within the calcium carbonate of these formations revealing information about past rainfall, and thus past monsoon seasons, and other precipitation events. These specific examples illustrate how isotopic records are being used to reconstruct past climate conditions and to understand the complexities of climate change. The IAEA supports these efforts by providing expertise, training, and access to analytical facilities, enabling scientists worldwide to contribute to this important research.