The greenhouse effect is a global process in which the atmosphere retains part of solar energy, so the energy returned into space is less than the solar radiation entering the Earth's atmosphere. This causes temperatures in the lower atmosphere to rise and leads to climate change.
Rising mean annual temperatures disrupt climatic balance and cause changes in water resources, forests, coastal regions, agriculture, technology and human health.
According to the Bulgarian Academy of Sciences' National Institute of Meteorology and Hydrology, 2007 was the warmest year since 1988. Most climate models simulate air temperature increases in Bulgaria of between 2 ˚C and 5 ˚C and a doubling of atmospheric carbon dioxide (CO2) concentrations.