How can we talk about climate change over the next 100 years when we can be sure of tomorrows weather?
Weather and climate are different. The methods used to forecast changes in weather and climate differ as well. Because the weather changes from day to day, current weather forecasts are reliable for roughly ten days. Climate, on the other hand, can be thought of as average weather, including weather’s variability over much longer time horizons (e.g., from year to year). Natural changes in our planet’s climate happen over the course of years, centuries and many millennia. Long-term climate forecasts are possible because scientists understand many of the factors that influence climate over such long periods, such as changes in the sun’s energy and the level of greenhouse gases in the atmosphere. Climate scientists do not claim to know how to predict day-to-day fluctuations (weather) over the 21st century. Rather, they are predicting how they think average temperature and precipitation (climate) will change due to human activities.
