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 Sample Forecasts of Future Temperature Change

In an effort to understand the complexities of the earth’s climate, scientists run computer simulations. In these simulations, equations represent the physical processes of the climate—such as seasonal changes in sunlight, evaporation and condensation of water, warming of the atmosphere by ocean waters, and so on.

Every simulation begins with assumptions. In generating the forecasts shown on this graph, researchers assumed that there would be no action to restrict future greenhouse gas emissions. But each line represents a different set of assumptions regarding future economic development and fundamental climate processes. These different assumptions generate very different future possibilities.

The researchers who created this graph explain that two-thirds of the overall difference between the extreme forecasts is due to uncertainty related to basic climate processes, such as the influence of clouds and ocean circulation. The rest of the difference reflects uncertainty in future emissions of carbon dioxide, which depend on population growth, economic growth, and technological changes.

 glossary glossary terms  

Click for definitions of words used on this page:

climate model
fossil fuels

View the full, printable version of the glossary.

Global Startospheric Temperature Anamolies

Sample Forecasts of Future Temperature Change
This graph shows seven forecasts by the same climate model—seven different possible futures for the earth’s temperature. All seven forecasts can be defended as reasonable.

Source: Massachusetts Institute of Technology Joint Program on the Science and Policy of Global Change

 questions about the data

question Why is predicting future climate so difficult?

email Email your own questions about this data set. 

 research connection  

Uncertainty is inherent in attempting to simulate future climate. One goal of the researchers who generated this graph was to address issues of uncertainty and predictability—and to quantify the uncertainty in climate prediction. In considering the future scenarios projected by different climate models, researchers observe where models agree and where they disagree. For some aspects of climate, virtually all models agree on the changes to be expected. On others, models disagree.

 related sites  

Uncertainty in Climate Change Policy Analysis - A detailed discussion of the uncertainties related to climate and their role in policy decisions.

Science @ NASA - This news story discusses the many difficulties of predicting climate change. - Contribute to research in climate change by running a climate simulation as a screensaver on your home computer.

Intergovernmental Panel on Climate Change (IPCC) - This chapter from the IPCC’s 2001 report describes how projections, predictions, and scenarios are used to predict the effects of global change.

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