Climate change involves both internal and external factors. External factors include solar variability, astronomical effects on the earth's orbit and volcanic activity, whereas internal factors include natural variability in the system and feedbacks within the atmosphere, ocean and land surface. The global temperature has increased by 0.5 degrees Celsius, with the greatest change in the middle latitudes. Long term changes are ascribed to astronomical forcing, while short term changes are linked to anthropogenic factors causing changes in atmospheric composition, including aerosol loading, depletion of ozone and destruction of vegetation. Climate change predictions with global climate models are undertaken for the next 100 years, and the mean global temperature may increase in the range of 1.4 to 5.8 degrees Celsius, together with sea level rise.