How are projections determined

How are projections determined

According to the Australian Academy of Science:

No scientific conclusion can ever be absolutely certain. However, a balanced assessment of the available evidence and prior knowledge allows us to attach levels of confidence to the findings of climate science.

There is a high degree of confidence in the broad conclusions of climate science. We are very confident of several fundamental conclusions about climate change: that human activities since the industrial revolution have sharply increased greenhouse gas concentrations; that these added gases have a warming effect; and that the Earth's surface has indeed warmed since the Industrial Revolution. Therefore, we are very confident that human-induced global warming is real.

"Climate projections" are model-derived estimates of future climate.

Dynamical climate models and emissions or concentration scenarios are used to produce climate change projections for the future. Global Climate Model (GCMs) show Queensland's rainfall and temperature will change into the future leading to warmer climate with a higher frequency of extreme weather events.

Global climate models have resolutions of hundreds of kilometres. However regional and more localised projections often require more point-specific climate information in order to capture fine-scale climate variations, particularly in regions with complex topography, coastal locations. To provide such information, scientists use the 'downscaling approach' to translate the data from the global climate models in order to provide more localised information on future climate change.

The modelling shows that some aspects of climate projections such as rainfall and regional changes are still quite uncertain.

Climate change models take into account different scenarios. These scenarios are based on sets of assumptions about possible alternative futures. Thousands of scientists and other technical experts involved with the Intergovernmental Panel on Climate Change (IPCC) have developed a set of future emission scenarios (Special Report on Emissions Scenarios (SRES) to assess how changes in economic growth, human population, social trends and technological advancements will affect future global emissions with consequent changes to global temperature (because of the 'enhanced' greenhouse effect) and sea level rise.

The exact amount of warming that will result from any particular trajectory for future greenhouse gas emissions cannot be projected precisely, because it depends on details of processes that reinforce or dampen disturbances to the climate system. Important processes involve clouds, aerosols, water vapour, ocean circulations, ice sheets and sea ice, and natural influences on greenhouse gas levels in the atmosphere.

Despite the uncertainties, climate modelling has an important role to play in informing public policy on climate change. Decisions on when and how to respond to climate change involve many factors that lie outside the realm of science, including ethical and economic considerations. An appropriate response will depend on value judgements and an assessment of the risks of various courses of action. Just as in any other sphere of human activity, decisions will need to be made before we have absolute certainty about the future.

The role of climate science is to inform these decisions by providing the best possible knowledge of climate outcomes and the consequences of alternative courses of action.

By 2100, our world will have changed in ways that are difficult to comprehend. Imagine predicting at the beginning of the 19th century the changes to population and technology that took place during the next 100 years.