Common Climate Questions

Q: How can we trust predictions about our climate for decades or centuries in the future?

A: When people wonder about the degree of certainty in global warming predictions versus next week’s weather report, they are confusing climate and weather. Predicting weather and predicting climate are different and pose different challenges.

Weather is individual, day-to-day atmospheric events; climate is the statistical average of those events. Weather is short-term and chaotic and is thus inherently unpredictable beyond a few days. Climate is long-term average weather and is controlled by larger forces, such as the composition of the atmosphere, and is thus more predictable on longer timescales. For the same reasons, a cold winter in one region does not disprove global warming.

As an analogy, while it is impossible to predict the age at which any particular man will die, we can say with high confidence that the average age of death for men in industrialized countries is about 75. The individual is analogous to weather, whereas the statistical average is analogous to climate.