Contributory factors to climate change

2.5.1 Greenhouse Gases – What are they?

Greenhouse gases such as carbon dioxide, methane, nitrous oxide and others, are a major contributor of rising temperatures. Concentrations of carbon dioxide in the atmosphere surpassed 400 parts per million in 2013. Likewise, methane and nitrous oxide concentrations are also breaking records.

These gases are released through human activities, and for the past four decades the majority of greenhouse gasses (78%) have come from industrial activity, the burning of fossil fuels for energy and livestock production.

Souce: IPCC, Climate Change 2014 – Synthesis Report

2.5.2 The Enhanced Greenhouse Effect

Sunlight passes through the earth’s atmosphere and warms the surface of the earth. Most of this heat is radiated back upwards. Gases within the Earth’s atmosphere, including carbon based greenhouse gases like carbon dioxide and methane; serve to re-absorb a large percentage of this heat and radiate in all directions. This process is known as the greenhouse effect and ensures the earth’s surface is warmed to a life-supporting average of 15 degrees Celsius.

Human activities have contributed to the extensive release of carbon based emissions, nitrous oxides and chlorofluorocarbons (CFCs). The buildup of these long lived greenhouse gases in the atmosphere has resulted an enhanced greenhouse effect; that causes more heat to be trapped and retained within the atmosphere than usual – leading to a gradual but steady rise in global surface and lower-atmospheric temperatures

The difference between the greenhouse effect and an enhanced greenhouse effect is explained in the diagram below.

2.5.3 The Albedo Effect

Albedo is the amount of light or radiation that is reflected from a surface. A surface with high albedo reflects most of the light/heat radiation and absorbs the rest, and vice versa. On Earth, the amount of light and heat reflected from the surface is a function of what is on our surface: forests, oceans, urban regions, deserts, and polar ice caps. As such changes in albedo contribute significantly to fluctuation in global temperature readings.

Bright ice and snow (high albedo) reflect 95% of heat radiation. However, with rising global temperatures, snow and ice has been melting, thus reducing the albedo for the region as previously iced over areas turn into land or ocean. This leads to a spiraling cycle known as the ice-albedo feedback.

Similarly, the clearing of forest areas results in a short term cooling effect as more radiation is reflected back into the atmosphere from the bare surface. However, because clearing of forest involves biomass combustion (remember the annual haze?), large amounts of carbon dioxide are released into the atmosphere, enhancing the greenhouse effect and contributing to long term global warming.

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