Climate change can be both natural or human induced. Natural climate changes are related to the flows of energy into and out of the earth-atmosphere system and ways in which energy is budgeted within the earth-ocean atmosphere system. Unfortunately, the explanation of the flows and interchanges is very complex and requires an examination of all parts of the system.

Climatic changes are currently now being attributed more to effects of human activities than to natural changes. Both inadvertent modification and deliberate modification of climate due to human activities have resulted in climatic changes within the last four to five decades. Inadvertent modification of climate through various activities such as urbanisation, industrialisation, farming, lumbering, overgrazing, irrigation and drainage of swamps has resulted in changes in global heat balance and therefore changes in climate. The farming practices and other human activities can increase the sedimentation and siltation of lakes and dams thus leadind to poor quality of water and affecting human livelihoods.

It is now well established that as a result of urbanisation, the climate of urban regions differs with those of their rural counter parts, and this is seen in the well-known effects of the ‘urban heat Island’. Agricultural activities such as clearing of natural vegetation and exposing the earth surfaces affect the reflectivity of the surface (surface albedo) and thus the heat balance.

Of the most serious human activities that have affected greatly climatic changes is industrialisation. The emission of gases as carbon dioxide (C0₂), methane (CH₄), Chlofluorocarbons (CFC’S, i.e. CF₂Cl₂, CFCl₃ and others), tropospheric Ozone (O₃) and nitrous Oxide (N₂O) have an important effect of trapping energy originating from the sun, in the form of heat near the earth’s surface, (the Green House Effect). It is generally agreed that the increased concentrations of the above Green House Gases (GHG’s) has led to a warming of the earth’s surface in the lower atmosphere and hence changes of climate. The effect of aerosols released to the atmosphere due to human activities cannot be neglected since they affect heat attenuation and therefore global energy balance.

   Stop and Think!

Explain how human activities affect the climate. Give examples from your local area.