How do scientists measure and predict climate change?
Relatively recently in geological history, humans have recorded data about climate and how it is changing. In order to compare current patterns, scientists need information about what the climate was like thousands, and even millions of years ago. Scientists analyse natural patterns, for example, in trees, coral and ice, in order to obtain this information.
- Trees
- Some trees have annual growth rings. Measurements of the width and density of the tree rings may be used to reconstruct warm seasons and annual temperatures.
- Corals
- Corals use carbon for calcification (the process by which coral grows its white skeleton). Some corals live for hundreds of years, and can give scientists an indication of how tropical and subtropical ocean temperatures have changed.
- Ice
- Scientists can analyse ice core samples from polar regions to ascertain levels of precipitation, concentrations of salt, acids, carbon dioxide and methane in past years.
Using this information in complex computer models, scientists can predict how our climate responds to increasing concentrations of atmospheric greenhouse gases. Scientists test the models on past climate information and for how well they replicate aspects of present-day climate such as the El Nino Southern Oscillation.
The global climate models used to develop the climate change projections have progressed from static atmospheric models in the 1970’s to complex, integrated and dynamic models that now include land surface, ocean and sea-ice, aerosols, carbon cycle and vegetation feedbacks. They are also much higher in resolution, due to increased computing capacity. The models are constantly being improved, which provides ever greater confidence in the climate change science and projections.
Projections are developed from these computer-based global climate models, using a range of future greenhouse gas emissions scenarios. There are uncertainties associated with future greenhouse gas scenarios and the output differences between models, resulting in a range of possible changes. There is greater confidence in projections for 2030 than for 2070. This is because it is difficult to predict emission rates far into the future. As a result, the range of possible change for 2030 is smaller than for 2070. The highest level of confidence in future climate change projections is for temperatures, due to the direct relationship between greenhouse gas concentrations and atmospheric temperatures. However, even for areas of highest confidence (eg. temperature rises), the final outcome still depends on future emissions.
Despite this uncertainty, more conclusive scientific evidence on climate change and its impacts is emerging every year. It is no longer a question of if climate will change, but how rapidly, by how much, and how humans will need to adapt to these changes. To find out more information on climate science, impacts and adaptation click here.
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For more information also see frequently asked questions (FAQs).
Last updated: 17 August 2006
