"Everyone talks about the weather, but no one can do anything about it". This is fairly accurate for weather, but is it true for climate? Climate is not just past weather, but it is a long-term average of weather and weather patterns. The sun and the earth's orbit seasonally influence both weather and climate; sunspots have an 11 year cycle. Other influences that have long-term effects are: volcanic eruptions, changes in the distribution of sea-ice and snow, asteroids hitting the earth and increasing carbon dioxide (CO2) from burning carbon based fuels. Molecules of CO2 absorb energy much like a greenhouse traps heat from the sun. The more CO2 in the atmosphere, the more warming occurs. CO2 in the atmosphere has been increasing dramatically over the past 100 years and unless the increase slows or stops, we can conclude that the earth will become warmer in the future. Tree rings and fossils can be used to offer us insight into the patterns of climate change but how can we predict what will happen to the climate in the future? The earth is far too big and complex to use as a laboratory, we must resort to using a mathematical representation or model to simulate it. Millions of years would be needed to calculate the behavior of the atmosphere by hand. Ultra fast computers that perform thousands of billions of operations per second are used to perform these calculations. However, computer models cannot perfectly simulate the weather or the climate. The models are accurate for some predictions, for example, deserts are geographically where they are predicted, but the models are limited. Current models cannot predict California's total winter rainfall. Scientists are constantly refining and improving the models so that better predictions can be made as gases like CO2 continue to have a profound influence on our climate. This is the fifth presentation in this year's Science on Saturday lecture series. The series is co-hosted by LLNL's Science & Technology Education Program and Sigma Xi.