ABSTRACT
The history of life on Earth began 3.8 billion years ago. The Earth’s climate changed throughout history, changes occurring on at least time scales of hundreds of thousands of years. This chapter examines the effect of natural forcings that contributed an insignificant fraction to the current rapid warming, which the models can evaluate. The human activity obviously is the main contributor to the fast warming in the last few decades. ‘Climate change’ is a long-term continuous change to average weather conditions or the range of weather or both happening together. The climate system consists of four major ‘components’ interacting among themselves influenced by several forcing mechanisms: atmosphere, hydrosphere, cryosphere, and biosphere and land surface. Biogeochemical cycles are subject to disturbance by human activities. Ocean circulation currents flow both in horizontal plane as well as in the vertical. Climate modelling is essential to deal with the enormous complexity of the climate system.
