Greenhouse gases and their relevance
Greenhouse gases (GHG) are gases in the atmosphere that absorbs and emits radiation within the thermal infrared spectrum. This process is the fundamental cause of the greenhouse effect. Many chemical compounds found in the Earth’s atmosphere act as “greenhouse gases.” These gases allow sunlight to enter the atmosphere. When the sunlight strikes the Earth’s surface, some of it is reflected back towards space as infrared radiation (longwave radiation). Greenhouse gases absorb these infrared radiations (longwave radiation) and trap them as heat in the atmosphere, and thus, greatly affecting the temperature of the Earth. Many gases exhibit these “greenhouse” properties with many of them occurring naturally. The primary greenhouse gases in the Earth’s atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone. Without these gases, Earth’s surface would have been colder than the present average of about 14 °C (57 °F)
The Greenhouse effect
The Earth’s surface receives energy from two main sources: the sun & the atmosphere. Solar radiation (energy from the sun) at the frequencies of visible light passes through the atmosphere to warm the earth’s surface. The earth then emits this energy at the lower frequencies of infrared thermal radiation back to the atmosphere. The Infrared radiation is absorbed by greenhouse gases, which in turn re-radiate much of the energy to the earth’s surface. This process is termed the greenhouse effect; named after the effect of solar radiation passing through glass and warming a greenhouse.
An increase in the concentration of greenhouse gases leads to an increase in the magnitude of the greenhouse effect. This is usually called enhanced greenhouse effect, and this result in global warming which ultimately leads to climate change.
Climate is the general weather conditions averaged over a long period of time. It also includes statistics other than the average, such as the magnitudes of day-to-day or year-to-year variations. Climate captures meteorological variable including temperature, humidity, atmospheric pressure, wind, precipitation, and many others in a given region over long periods. Climate is thus said to be the sum of all statistical weather information that helps describe a place or region. It also applies to large-scale weather patterns in time or space such as an ‘Ice Age’ climate or a ‘tropical’ climate. On the other hand, weather is the present condition of these variables over shorter periods. The climate of any location on the earth’s surface is affected by the terrain, the altitude, and the latitudes.
Climate Change refers to a statistically significant variation in either the mean state of the climate or in its variability or both, persisting for an extended period (typically decades or longer) – IPCC 2001. According to the United Nations Framework Convention on Climate Change (UNFCCC), climate change refers to a change of climate that is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and that is in addition to natural climate variability observed over comparable time periods.
According to the David Suzuki Foundation, climate change occurs when long-term weather patterns are altered, mostly through human activity. Global warming is one measure of climate change, and is a rise in the average global temperature
Climate Variability is the way climatic variables such as temperature and precipitation depart from some known average state – either above or below the average value. Even in a stable climate regime, there will always be some variation; either wet or dry years; warm or cold years, etc. There will hardly be a year with completely “average” or “normal” climate conditions. The challenge for scientists is to determine whether any increase or decrease in precipitation, temperature, frequency of storms, sea level, etc. is due to climate variability or climate change.
The causes of climate change
Most climate scientists have come to the conclusion that Climate Change is caused by global warming, which has two main causes; natural causes and anthropogenic (human induced) causes. The natural causes of global warming include changes in the earth’s orbit, the solar variations, drifting continents and volcanic eruptions.
In its recently released Fourth Assessment Report, the IPCC concluded that there was a more than 90 percent probability that human activities over the past 250 years have warmed the earth. They contend that the industrial activities that our modern civilization depends on have raised atmospheric carbon dioxide levels for example from 280 parts per million to 379 parts per million in the last 150 years. They also concluded that there was a more than 90 percent probability that human-produced greenhouse gases such as carbon dioxide, methane and nitrous oxide have caused much of the observed increase in the Earth’s temperatures over the past 50 years. They said the rate of increase in global warming due to these gases is very likely to be unprecedented within the past 10,000 years or more. (IPCC, 2007)
It is believed that the anthropogenic influences are the greatest causes of global warming. Changes in the concentration of greenhouse gases as a result of human activities have greatly influenced the earth’s climate. Global atmospheric concentrations of CO2, methane (CH4) and nitrous oxide (N2O) have increased markedly as a result of human activities since the 1750s.
Current developmental processes require a lot of energy and this has led to the burning of huge quantities of fossil fuels (oil, natural gas and coal) for power generation and transportation. Industrial processes in recent years release large quantities of carbon dioxide (CO2) and other greenhouse gases into the atmosphere leading to increases in their concentrations beyond the acceptable levels. The forests which serve as carbon sink are being cleared for timber and other developmental processes, leading to an increase in the carbon load of the atmosphere. The flaring of natural gas in oil exploration and the burning of biomass all contributes to the increasing of CO2 in the atmosphere. It is worthy to note that carbon dioxide (CO2) is the most significant anthropogenic greenhouse gas. Its annual emissions grew by about 80% between 1970 and 2004. Atmospheric concentrations of CO2 (379ppm) and CH4 (1774ppb) in 2005 exceed by far the natural range over the last 650,000 years.
Methane (CH4), a greenhouse gas which is much more potent at trapping heat than CO2 is produced through the anaerobic decomposition of organic matter in biological systems. Methane levels in the atmosphere have been enhanced through a number of anthropogenic activities including solid waste landfill sites. The decomposition of organics in the landfills produces large quantities of methane. Rice production in lowlands (wetland) requires a waterlogged field. This production system generates methane into the atmosphere. The digestive processes in ruminants produce a lot of methane in the guts of the animals and released into the atmosphere, hence livestock production also contributes to the methane levels in the atmosphere. The production and distribution of fuel from fossil sources also generates appreciable quantities of methane into the atmosphere.
Nitrous Oxide (N2O) is about 300 times more effective in trapping heat energy than carbon dioxide. It is produced naturally through the microbial processes of nitrification and de-nitrification in biological systems. Agricultural activities contribute immensely to the increasing loads of this greenhouse gas in the atmosphere. The application of nitrogen-based chemical fertilizer to agricultural fields contributes to this problem. Industrial production processes and the burning of solid waste also release Nitrous Oxides into the atmosphere. The burning of fossil fuel also contributes to the N2O levels in the atmosphere.
HFCs, PFCs and other sulphur compounds have very long atmospheric lifetimes and their concentrations in the atmosphere can irreversibly accumulate. These gases are released into the atmosphere through industrial processes like aluminium smelting, electric power transmission and distribution, and the manufacturing of semi-conductors.
Evidence of climate change
Increase in global temperature is one of the key indicators if climate change. Eleven of the last twelve years (1995-2006) rank among the warmest years in the instrumental record of global surface temperature (since 1850). The temperature increase is widespread over the globe and is greater at higher northern latitudes. Land regions have warmed faster than the oceans.
Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice and rising global average sea level (IPCC 2007)
Rising sea level is consistent with warming. Global average sea level has risen since 1961 at an average rate of 1.8 [1.3 to 2.3] mm/yr and since 1993 at 3.1 [2.4 to 3.8] mm/yr, with contributions from thermal expansion, melting glaciers and ice caps, and the polar ice sheets.
Global climate change has already had observable effects on the environment. Glaciers have shrunk, ice on rivers and lakes is breaking up earlier, plant and animal ranges have shifted and trees are flowering sooner. Effects that scientists had predicted in the past would result from global climate change are now occurring: loss of sea ice, accelerated sea level rise and longer, more intense heat waves.
Scientists have high confidence that global temperatures will continue to rise for decades to come, largely due to greenhouse gasses produced by human activities. The Intergovernmental Panel on Climate Change (IPCC), forecasts a temperature rise of 2.5 to 10 degrees Fahrenheit over the next century. According to them, the extent of climate change effects on individual regions will vary over time and with the ability of different societal and environmental systems to mitigate or adapt to change.
The IPCC predicts that increases in global mean temperature of less than 1.8 to 5.4 degrees Fahrenheit (1 to 3 degrees Celsius) above 1990 levels will produce beneficial impacts in some regions and harmful ones in others. Net annual costs will increase over time as global temperatures increase. The IPCC states that, “the range of published evidence indicates that the net damage costs of climate change are likely to be significant and to increase over time.”
Some of the regional impacts of global change forecast by the IPCC include;
- A decreasing snowpack in the western mountains of North America; 5-20 percent increase in yields of rain-fed agriculture in some regions; increased frequency, intensity and duration of heat waves in cities that currently experience them.
- Freshwater availability projected to decrease in Central, South, East and Southeast Asia by the 2050s; coastal areas will be at risk due to increased flooding; death rate from disease associated with floods and droughts expected to rise in some regions.
- Gradual replacement of tropical forest by savannah in eastern Amazonia in the Latin America; risk of significant biodiversity loss through species extinction in many tropical areas; significant changes in water availability for human consumption, agriculture and energy generation.
- Increased risk of inland flash floods in Europe; more frequent coastal flooding and increased erosion from storms and sea level rise; glacial retreat in mountainous areas; reduced snow cover and winter tourism; extensive species losses; reductions of crop productivity in southern Europe
- By 2020, between 75 and 250 million people are projected to be exposed to increased water stress in Africa; yields from rain-fed agriculture could be reduced by up to 50 percent in some regions by 2020; agricultural production, including access to food, may be severely compromised.
Contribution of Greenhouse effect to climate change
Greenhouse gases in their natural occurrence are beneficial to the environment. Increasing concentrations of these greenhouse gases in the atmosphere generally produce an increase in the average temperature of the Earth. Rising temperatures may, in turn, produce changes in weather, sea levels, and land use patterns, thus, “climate change.”
Climate assessments generally suggest that the Earth’s climate has warmed over the past century and that human activity affecting the atmosphere is likely an important driving factor. A study by the National Research Council (2001) stated that, “Greenhouse gases are accumulating in Earth’s atmosphere as a result of human activities, causing surface air temperatures and sub-surface ocean temperatures to rise. Temperatures are, in fact, rising. The changes observed over the last several decades are likely mostly due to human activities, but we cannot rule out that some significant part of these changes is also a reflection of natural variability.”
It can therefore be concluded that the Greenhouse Effect through the activities of the naturally occurring greenhouse gases does not cause Climate change. Climate change is caused by the enhanced greenhouse gases mainly through anthropogenic activities.
- http://en.wikipedia.org/wiki/Greenhouse_effect (accessed 4th June 2013)
- http://www.davidsuzuki.org/issues/climate-change/science/climate-change-basics/climate-change-101-1/ (accessed 4th June 2013)
- IPCC, 2007, Climate Change 2007: Synthesis Report – Summary for Policymakers
- 4. National Research Council, 2001, Advancing the Science of Climate Change