The Enhanced Greenhouse Effect

An increase in the concentration of greenhouse gases in the atmosphere results in more heat being retained and an overall warming of the Earth’s temperature. Although they make up a small percentage of atmospheric gases, changes in the concentration of greenhouse gases have a huge effect on the balance of natural processes. 


The core concern about climate change is human potential to alter the climate through activities that are a result of our way of life and how we treat the natural environment.  There have been significant technological advances over the past 60 to 100 years that have offered humankind countless benefits and conveniences. These increases in human activity, however, have also led to an additional release of greenhouse gases that have placed stress on natural processes.


Some of the gases, such as carbon dioxide, water vapour, methane, nitrous oxide, and ozone are the result of both natural and human processes. Others, notably fluorinated gases, are generated solely by human activities.  The sources of these gas emissions include burning fossil fuels to power our way of life, industrial processes, urbanisation and land use, agriculture and deforestation. Since the beginning of the industrial revolution, concentrations of carbon dioxide in the atmosphere have increased nearly 30 per cent methane concentrations have more than doubled, and nitrous oxide concentrations have risen by about 15 per cent.

Trends in Atmospheric Concentrations and Anthropogenic Emissions of Carbon Dioxide - Source Oak Ridge National LaboratoryCarbon dioxide is the single largest contributor to the enhanced greenhouse effect. Increases in carbon dioxide emissions account for approximately 70 per cent of the enhanced greenhouse effect. Using ice cores from the Antarctic, scientists estimate that the concentration of carbon dioxide in the atmosphere in the pre-industrial era had a value of  approximately 280 parts per million (ppm). Measurements in 2005 put it at 379 ppm.  The 2005 figures also tell a story of alarming growth. The 2005 carbon dioxide levels exceeded the natural range of atmospheric carbon dioxide over the last 650,000 years (180 to 300 ppm). In addition, even though there has been year to year variability (at an average of 1.9ppm), the annual growth rate of carbon dioxide concentrations in the atmosphere was larger during the 10 years between 1995 and 2005  than  it had been since the beginning of continuous direct atmospheric measurements between 1960 and 2005 (average: 1.4 ppm per year) (IPCC, 2007).


The carbon dioxide source and sink imbalance

It is true that natural sources of carbon dioxide - plant respiration and decomposition of organic matter - generate more than 10 times the amount of carbon dioxide produced by human activities such as driving motor vehicles, heating homes and powering factories. However, in the past, natural processes that remove or sequester carbon dioxide from the atmosphere, namely photosynthesis and the carbon reservoir function of the oceans, balanced out these releases. 


We now have a situation where not only are additional sources producing and emitting carbon dioxide in significant quantities but the natural sinks that remove carbon dioxide are also being compromised. Trees and forests are being cut down for a variety or reasons, including agriculture and human settlements. At the same time, oceans, including the North and South Atlantic oceans, are reaching their carbon dioxide saturation point because their absorptive capacity is failing to keep pace with the increase in carbon dioxide emissions. A 10-year study by the University of East Anglia found that the North Atlantic halved its absorption of carbon dioxide between the mid-90s and 2000 to 2005. Scientists previously thought the carbon sink function of the oceans would help offset the increase in anthropogenic carbon dioxide emissions. However, this appears not to be the case. Even though a decrease in the ability of the oceans to absorb carbon dioxide was anticipated by scientists and even factored into some climate models, it seems to be happening 40 years earlier than expected.