The global system has gone through changes throughout Earth’s history. Recent change has been driven by human activities, primarily burning of fossil fuels.
Climate is the average and variation of weather over long periods of time. The climate system is a complex, interactive system driven by incoming solar radiation, consisting of the atmosphere, land surface, snow and ice, oceans and other bodies of water, and living things.
The Enhanced Greenhouse Effect
Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations. The rate of surface warming over the past 50 years is greater than any temperature rate of change in the history of our species.
The climate system responds to changes in radiative forcing very slowly, over centuries. As a result, we have already committed to future warming due to past emissions, and our actions now will impact the global climate for thousands of years.
These numerical models of the climate system allow scientists to project the impacts of current and future human activities on global and regional climate. The physics, chemistry, and biology that drive Earth’s climate system are (for the most part) understood and can be modeled quantitatively.
There is inherent uncertainty in attempting to simulate or predict the climate system, just as there is in attempting to predict local weather. Through the use of statistical methods and climate modeling, we can quantify uncertainty by estimating the probability of different possible outcomes.