Certainty

• There is a natural greenhouse effect.
• Atmospheric greenhouse gas concentrations are increasing as a result of human activities.

Uncertainty

Major scientific uncertainties relate to:

• sources and sinks of greenhouse gases and their chemical reaction in the atmosphere;
• the role of clouds in the greenhouse process;
• how oceans exchange energy between the Earth and the atmosphere and how they influence the rate of climate change and regional effects;
• the role of polar ice sheets and their effect on sea level in a warmer and wetter climate.

Because of these scientific uncertainties there is:

• no firm forecast of the amount of warming to occur as a consequence of the enhanced greenhouse effect;
• a low level of confidence in predictions of changes to rainfall patterns even at the most general level;
• no confidence in estimates of any aspect of climate change at the regional level;
• no evidence that weather variability and extremes of weather will change in the future;
• little understanding of how natural systems could adapt or evolve in a greenhouse gas-enriched environment.

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