Global warming may be defined as the increase in the average temperature of the Earth. According to the United States Environmental Protection Agency (EPA), “Earth’s average temperature has risen by 1.4 degrees Fahrenheit over the past century”. The Earth’s average temperature is expected to continue to increase in this century by 2 to 11.5 degrees Fahrenheit.The graph below shows the record of average global temperatures from 1880 to early this century. The graph shows that during this period, there has been an increase in global temperature of just under 1 degree Celsius.
Although the change in temperature may seem small, it is worth noting that small changes in the Earth’s average temperature can have a major impact on climate and the environment.
Causes of Global Warming
There have been many periods when the average temperature of the Earth has increased and then eventually decreased naturally. These fluctuations in the Earth’s temperature occur in cycles which take many thousands of years to complete. However, in recent history, the increase in the Earth’s temperature has been largely the result of man’s activities.
Our atmosphere contains gases which are known as greenhouse gases. Sunlight enters the Earth’s atmosphere as shortwave radiation and warms the Earth’s surface. The Earth’s surface releases some of this radiation as heat. Greenhouse gases absorb some of this heat, preventing it from being released into space. It can be said that these gases act like a blanket, helping to keep the Earth warm. Without them, the Earth would be an extremely cold place. Some of the main greenhouse gases are carbon dioxide, methane, nitrous oxide and water vapour:
- Carbon dioxide is released into the atmosphere naturally through various means such as wildfires, volcanic activity and respiration. We release additional carbon dioxide through human activities especially the burning of fossil fuels for energy.
- Methane is released into the atmosphere as a result of agricultural activities such as the rearing of livestock and the production and processing of natural gas. Organic matter rotting in dump sites and elsewhere also releases methane. According to the EPA, “Globally, over 60% of CH4 [methane] emissions come from human activities.”
- Nitrous oxide is produced naturally as part of the Earth’s nitrogen cycle. We also release nitrous oxide into the atmosphere when we burn fossil fuels and also when we produce and use artificial fertilizers containing nitrogen.
- The amount of water vapour in the atmosphere is regulated by natural processes such as evaporation and rainfall. Therefore human activities have not had a significant impact on the amount of water vapour in the atmosphere.
A major cause of global warming is the release of greenhouse gases into the atmosphere by human activities. Greater quantities of greenhouse gases in the atmosphere cause the Earth to be warmer than it would normally be. For the last 200 years or so, we have released very large quantities of greenhouse gases into the atmosphere. Most of these gases are produced when we burn fossil fuels to provide energy. Carbon dioxide (CO2)is the most significant greenhouse gas. The substantial increase in CO2 in our atmosphere is the main cause of global warming.
For a very long time, the amount of carbon dioxide in our atmosphere was relatively stable. However, since the industrial revolution, it has increased significantly. According to the EPA, “Human activities currently release over 30 billion tons of CO2 into the atmosphere every year.” Research at the Mauna Loa Observatory has shown that the amount of carbon dioxide in our atmosphere has increased from about 280 parts per million in the 1700’s to 390 parts per million in 2010.
Deforestation also contributes to global warming. Trees and other plants absorb carbon dioxide and use it during photosynthesis. Therefore our forests play a major role in using up the carbon dioxide in the atmosphere. Sadly, an estimated 18 million acres of forest is lost every year. When we clear forested areas, we are reducing the Earth’s ability to deal with carbon dioxide. Fewer trees means more carbon dioxide in the atmosphere.
This video outlines the causes of global warming.
Effects of Global Warming
The Earth is currently experiencing some of the effects of global warming. As the Earth’s temperature continues to rise, experts are predicting even more serious effects. Some of the effects (and possible future effects) of global warming include:
Rising sea level: As the average temperature of the Earth rises polar ice in the Arctic and Antarctic melts. Glaciers and ice sheets in places such as Greenland, North America and Europe are also melting. This water ends up in our oceans causing a rise in sea level. Sea level has risen 8 inches since 1870. During this century, sea level is expected to rise at an even faster rate. Some experts predict a rise in sea level of over a meter by 2100. As sea level rises, low lying areas near the coast are threatened.
Disruption of ocean currents: Ocean currents help to regulate the Earth’s temperature. They bring warm water to the colder areas in the north and south of the planet. Ocean currents also bring colder water toward the Equator. Scientists believe that the large quantities of fresh water pouring into our oceans could disrupt ocean currents. If the ocean currents are not able to redistribute heat efficiently, some temperate areas may have colder winters.
More frequent extreme weather events: In the past forty years or so, extreme weather events such as droughts, heat waves and storms have been occurring more frequently. Global warming is believed to be responsible for this. Scientists predict that extreme weather events will become more frequent and more intense as the Earth warms up.
Changing rainfall patterns: Experts believe that rainfall patterns may change significantly. Some areas, such as the subtropics, may receive less rainfall and experience more frequent droughts. Other areas, such as the higher latitudes, may receive more rainfall. In some areas it is expected that heavy rainfall will be more frequent, increasing the likelihood of floods.
Impact on plants and wildlife: As world temperatures have increased, some plants and animals (including parasites and disease causing organisms) are now inhabiting regions which were once too cold for them to survive. They may pose a threat to the native species in these areas. Also some organisms may find it difficult to adapt to the changing climate and may become extinct. Polar bears, for example, are having difficulties coping with the effects of rising temperatures in the arctic.
The video below outlines some of the effects of global warming.