ZIMSEC O Level Geography Notes: People and Weather: Accidental Changes

Acid Rain

  • The smoke from burning fuels and chemical industries rises into the air and mixes with water vapour.
  • When the rain falls down it becomes acidic.
  • The acid rain is a weak acid made up of sulphuric and nitric acids.
  • Over, a long time (years for example), the rain eats into limestone installations as well as natural landscapes, stone walks, statues and metals.
  • It also destroys vegetation as it has done to entire forests in the Eastern countries like the Black Forest in Germany.
  • Has negatively impacted on tree growth in Scandinavian countries.
  • Since acids accrue in water they poses a health risk to humans and animals.

Carbon Dioxide and Global Warming

The Greenhouse Effect

  • Due an increasingly industrialized world a lot of Carbon Dioxide is being emitted into the atmosphere from industries, motor vehicles, machinery and other human activities.
  • The solar irradiation from the sun comes mainly in the form of short UV radiation (light).
  • These is converted into longer infra-red waves (heat) when it reaches the earth’s surface.
  • Some of the heat is radiated back into the atmosphere by the earth’s surface.
  • Due to increased carbon emissions the amount of carbon dioxide in the atmosphere has increased.
  • This layer of Carbon Dioxide has an insular effect, it acts as a blanket preventing the longer waved infra-red waves from escaping back into space.
  • The result is a general increase in the world’s mean temperatures.
  • This is known as global warming.
  • The effects of global warming include a general increase in mean temperatures in some places, the melting of Polar ice resulting in sea level changes: this leads to flooding in low lying coastal areas, destruction of Polar ecosystems, persistent droughts in some areas, flooding and mudslides due to excessive rain in other areas for example Indonesia, freak weather storms and increasingly unpredictable weather, droughts and increased aridity in some areas.
  • The effects of global warming are being compounded by deforestation.

NB The school of thought that attributed Global Warming to naturally occurring Solar flares has since been continuously shown as there is no evidence to support their theory. It is continually peddled by those in the vested Industries like Oil and developed nations like the US who fear the effects of governmental corrective actions on their businesses. As with the very clear harmful effects of smoking, it will eventually become a clear fact that global warming is real claiming that global warming is a myth is quackery science that you as a Geography student must not subscribe to.



  • The high demand for timber, wood and land cultivation has led to the continuous clearance of forests.
  • This reduces the humidity in the atmosphere and subsequently rainfall with long term effects of climate change and desertification.
  • Deforestation also reduces the amount of trees which convert carbon dioxide back into oxygen resulting in a retrogression on the speed of global warming.

Ozone layer depletion

Ozone Layer depletion and its effects. Image by Tutor Vista.

Ozone Layer depletion and its effects.

  • In the upper layers of the earth’s atmosphere (between the stratosphere and the troposphere) there is a layer known as the Ozone Layer.
  • It is composed of special bonds of Oxygen (O3) and about 30 km from the earth’s surface.
  • It acts a shield by blocking out the sun’s dangerous UV radiation from reaching the earth.
  • It is being depleted by chemicals from factories and some antiquated forms of aerosol sprays.
  • These make emissions containing nitrous oxide compounds, bromine and  chlorine compounds.
  • These chemicals are often referred to as organohalogen, chloroflurocarbons (CFCs) and Bromoflurocarbons.
  • They are depleting/reducing the Ozone layer by chemically breaking it down.
  • This has resulted in Ozone holes in some places.
  • This results in higher cases of non-melanoma skin cancer, eye cataracts and blindness and weakening of human immune systems (immuno-supression) to people living underneath these Ozone holes.
  • Other effects include: reduced plant growth harming agricultural activities as well as natural vegetation, reduction in plankton populations (these is the major source of food for most fish and features prominently in marine ecosystems), loss of marine biodiversity, higher incidents of cancer in domestic animals, adverse effects on flowering and pollination of plants and damage to important synthetic materials like plastics and rubber.

To read and learn about the Urban Heat Islands follow the link. The Urban Heat islands are a unique example of how humans can comprehensively but un-intentionally affect weather.

Go to the Geography Notes page  to access more topics.