Climate Change: Past And Future

The problem of human-caused climate change (commonly referred to as global warming) is now well known: the concentrations of ‘greenhouse gases’ in the atmosphere (notably carbon dioxide and methane) are now well above their pre-industrial levels, primarily due to our use of fossil fuels (coal, oil, and natural gas) but also due to deforestation and agricultural practices. As greenhouse gases accumulate in the atmosphere, more heat energy from the Earth’s surface is intercepted before escaping to space, thereby causing the atmosphere to warm.

Of course greenhouse gases are not the only factor influencing the Earth’s climate, and much of the complexity surrounding the global warming issue (such as the amount, rate and pattern of warming) involves trying to understand the knock-on effects that the rise in greenhouse gases will have on other parts of the climate system. There are also natural variations in climate that occur on a range of different timescales, and there are variations, both natural and human-caused, in the way the greenhouse gases themselves cycle between atmosphere, land, and oceans. In short, understanding and predicting climate change is far more complex than it may at first seem.

Studies of Antarctica, particularly analyses of Antarctic ice cores, have played a crucial role in this endeavour. As described further below, the ice cores have enabled scientists to reconstruct past climate changes spanning hundreds of thousands of years. Past variations in climate due to natural causes are now far better understood than they used to be, and this has provided vital context against which to assess more recent changes caused by people. The polar regions are also often described as the ‘canary in the coal mine’ for detection of global warming, and some of the research stations discussed in Regional climate variation and weather, provide important weather data for assessing the polar response to the rise in greenhouse gases. And, as Antarctica holds about 90% of all the ice on the planet, what happens in Antarctica will have major effects on the rest of the world.

Before looking further at what we have learned about climate change from Antarctica, it’s worth reviewing some key concepts about evidence and timescales.Cold facts

Past climate change in Antarctica: the evidence in ice

Antarctica hasn’t always had the climate that it has now. In the geological past Antarctica has been much warmer, and fossils indicate that at various times trees have covered much of the continent. These warm times for Antarctica were the result of different tectonic configurations and patterns of ocean circulation many millions of years ago (see Key factors behind Antarctica’s climate). For at least the last 6 million years, ice has covered most of the continent.

In contrast with the much older geological evidence, the ice core record extends from the present day back to about 800 000 years ago. Over this time span the distribution of land and sea across the world has been essentially the same as today; and therefore, the changes recorded in Antarctic ice are more informative about how the climate varies under the present tectonic configuration and how it may change in the near future.

Ice cores are obtained by drilling into an ice sheet or glacier and extracting cylindrical sections of ice. These sections of ice represent many thousands of years of snow accumulation: the addition of snow each year buries underlying layers of snow, and over time these layers become compressed into glacier ice. Each layer of an ice core is derived from snow that fell at a certain time in the past, and each layer is like a time capsule, containing information about what the atmosphere was like at the time the snow fell.