Science Objects are two hour on-line interactive inquiry-based content modules that help teachers better understand the science content they teach. This Science Object, co-developed between NOAA and NSTA, is the fourth of four Science Objects in the Ocean’s Effect on Weather and Climate SciPack. It explores how Earth’s climate has changed in the past and how it may change in the future. Climate change may occur as a result of changes in Earth's surface, atmosphere, and oceans. Such changes may be abrupt (such as gas and dust from volcanic eruptions or asteroid impacts) or may occur over very long times (such as changes in landscape or increase in carbon dioxide levels in the atmosphere). Even relatively small changes in atmospheric or ocean content and/or temperature can have widespread effects on climate if the change lasts long enough. Since the industrial revolution, the concentration of greenhouse gases in the atmosphere has increased at an unprecedented rate. Though climate change and changes in the composition of the oceans and atmosphere are natural, present modifications far exceed natural rates.