The temperature of the Earth is determined by the balance between energy from Sun and its loss back into space. Of Earth’s incoming solar short-wave radiation (mainly ultraviolet (UV) radiation and visible ‘light’) nearly all of it passes through the atmosphere without interference. The only exception is ozone that luckily for us absorbs energy in the high-energy UV band restricting how much reaches the surface of the Earth as it is very damaging to cells and DNA. About one-third of the solar energy is reflected straight back into space. The remaining energy is absorbed by both the land and ocean. This warms them up, and they then radiate this acquired warmth as long-wave infrared or ‘heat’ radiation. Atmospheric gases such as water vapour, carbon dioxide (CO2), methane (CH4), and nitrous oxide are known as greenhouse gases (GHGs) as they can absorb some of this long-wave radiation, thus warming the atmosphere. This effect has been measured in the atmosphere and can be reproduced time and time again in the laboratory. We need this greenhouse effect because without it, the Earth would be at least 35°Celsius (C) colder, making the average temperature in the tropics about —10°C. Since the industrial revolution we have been burning fossil fuels (oil, coal, natural gas) deposited hundreds of millions years ago, releasing the carbon back into the atmosphere as CO2 and CH4, increasing the ‘greenhouse effect’ and elevating the temperature of the Earth. In effect we are burning fossilized sunlight.
Cause of Climate Change:
The major source, accounting for one-fifth of global CO2 emissions, is as a result of land-use changes. These emissions come primarily from the cutting down of forests for the purposes of agriculture, urbanization, or roads. When large areas of rainforests are cut down, the land often turns into less productive grassland with considerably reduced capacity for storing CO2. Between 2015 and 2044 the world will put half a trillion tonnes of CO2 into the atmosphere, which is the same amount that was emitted between 1750 and 2015. This is because rapidly developing countries such as China, India, South Africa, Brazil, etc., are increasing their emissions of GHGs at a huge rate—economic development being closely associated with energy production. For example, in 2007, China became the biggest emitter of CO2 in the world, overtaking the USA. However, when considered per capita, the Chinese emissions are four times lower than those of the USA, who are top of the per-capita list.
Credit: Climate Change: A very short introduction