Global warming is a universally accepted phenomenon. The activities of mankind have elevated the levels of greenhouse gases in the atmosphere. These greenhouse gases have led to warming of the planet. The main greenhouse gas is carbon dioxide.
Analysis of air bubbles trapped in polar ice have allowed us to monitor the change in atmospheric carbon dioxide levels over time. Between 150,000-1,000 years ago, analysis indicates that carbon dioxide levels in the atmosphere fluctuated between 200-300 µmol per mol l (this SI unit has replaced parts per million). 1000-150 years ago, atmospheric carbon dioxide levels were 280 µmol per mol. 150-10 years ago, atmospheric carbon dioxide levels were 352 µmol per mol. This increase has been exponential and is accelerating.
In the last 50 years, the atmospheric concentration of carbon dioxide has increased by 30% over pre-industrial levels. The main reasons for this carbon dioxide enrichment have been the burning of fossil fuels and the clearing of vegetation from land particularly tropical forests (Stuiver, 1978).
Carbon dioxide is termed a greenhouse gas. This means that it absorbs long wave radiation more efficiently than short wave radiation. Short wavelengths predominate in sunlight and penetrate the atmosphere warming the Earth. The Earth then returns longwave radiation. This longwave energy is absorbed by greenhouse gases such as carbon dixoide which, in turn, radiate part of the energy (in long wavelengths) back to the Earth so warming it. Experts now agree that global warming will happen and, in fact, it is already occurring. Fifteen of the worlds hottest years, since recorded history have all occurred in the 1990's. This is resulting in well publicised phenomena such as:
- Changes in climate and rainfall pattern.
- Changes in ecosystem composition.
- More extreme weather with, in the UK, wetter winters and hotter, drier summers.
- Increasing severity of 'urban heat islands'.
The concept of sustainability is a philosophical stance or ideal. It is based upon our looking back at the damage that our interaction with our environment has caused and a striving forward to ensure that our actions today do not adversely affect the world for generations to come.
Sustainable development is the pragmatic application of the philosophy. It has to be accepted that protection of the environment must go hand in hand with allowing both society and business to support itself and develop. If protection of the environment ignores society and business, then society and business will ultimately exclude environmental concerns.
An integral part of the drive for good sustainable practice, particularly in the commercial sector, is accountability for the production of the major greenhouse gas responsible for global warming- carbon dioxide. Good sustainable practice in itself can only reduce the production of carbon dioxide. The only universal process that removes carbon dioxide from the atmosphere is photosynthesis. Photosynthesis is the chemical reaction by which plants use the sun's energy to combine water and carbon dioxide to make sugars for growth. Thus the only process that can claim to remove carbon dioxide is the utilisation of plants. For this reason roof planting on a large scale and collectively driven at the legislative level, could play a crucial role in the sustainable development practices of the future.