Since the formation of the atmosphere, global climate system has the tendency to change in time and space and this change is related with the natural changes of the other components of the earth/atmosphere system. However, since the mids of 19th century a new era has begun where in addition to these natural changes human activity started to affect the global climate.

Since the beginning of industrialization in 1850s especially as a result of burning fossil fuels, land use changes, destruction of forests and distorted industrialization, greenhouse gases accumulated within the atmosphere, affecting the chemical characteristics of the atmosphere and in the long term causing climate change on a global scale.

Infrared rays emitted by the sun reach our planet after a journey of millions of kilometers. Part of these rays warm the earth and the seas by hitting the earth; the other part is reflected to space after striking the ground. However, greenhouse gases in the atmosphere prevent these infrared rays to pass through the atmosphere by absorbing them. This absorption event leads to the heating of the atmosphere.

The more the concentration of greenhouse gases in the atmosphere, the more heat is absorbed. As a result, average temperature of the Earth rises.

Global warming due to increases in greenhouse gases refers to increases in global average surface temperature. The most important reason of global warming is the rapid increase of greenhouse gas emissions like carbon dioxide (CO2) and methane (CH4) in the atmosphere.

Changes of concentrations of GHGs

  Before Industrialization 2005 Change %
CO2 280 ppm 379 ppm % 35
CH4 715 ppb 1774 ppb % 148
N20 270 ppb 319 ppb % 18

According the 4th Assessment Report of Intergovernmental Climate Change Panel - IPCC in 2007, global warming is an undisputed fact and humans are responsible for the major part of it. The total amount of emissions of the 6 major greenhouse gases from the energy industry, manufacturing, agriculture, forestry and land use have increased by 70 % in between 1970-2004 and increased to 49 billion tons CO2eq. During the process, the annual growth rate in between 1995-2004 is almost 2 times the annual growth rate in between 1070-2004. 65 % of human related greenhouse gases are caused by burning fossil fuels. Global average surface temperature has increased 0.74 °C in the last century.

This warming trend after the 1980's became more evident and during this period high temperature records were broken. In terms of global averages year 1998 was recorded as the warmest year since the temperature observations and measurements began in 1860.

Due to the rising temperature, significant changes in socio-economic and ecological systems and human life are expected to occur worldwide such as, changes in the hydrological cycle, land and sea ice melting, the contraction of surface snow and ice cover, sea level rises, increased frequency of severe weather events, drought, desertification, and increasing outbreak of diseases and pests. Some of these changes have already started especially since the last quarter of 20th century.

According to relevant research, an average of 2 °C and above temperature increase compared to Industrial Revolution levels will have dangerous and irreversible effects. It is very important to limit the temperature increase by 2 °C in this century. However it hardly seems possible with business as usual scenarios and standards of living.

Some events expected to occur after global warming;

International History of Climate Change