During the last century, Earth’s temperature has risen by 0,5ºC. This global warming is a consequence of greenhouse effect, caused by nothing else but human activities.
I would divide the greenhouse effect into two main types: the “good” and the “bad”. I even think there is no mid- type or sort of golden middle way – greenhouse effect can be only good or only bad (an explanation will be given later). Earth’s atmosphere is very similar to greenhouse glass - it is transparent to sunlight, which warms it, but it keeps a part of both earth and sunlight’s warmth from escaping back into free space. This effect is due to several greenhouse gases, including carbon dioxide (CO2), nitrous oxide (N2O), methane (CH4), chlorofluorocarbons (CFCs - freons) and water vapor. Without these gases and the “good” greenhouse effect, the Earth would be very cold (different sources say different numbers, but surely it would be deeply below zero and even oceans would be frozen) and there could be no life on it. Nowadays, the atmospheric concentrations of greenhouse gases are rising as a result of human activities - that is how good (natural) greenhouse effect becomes bad or even dangerous for Earth and people living on it. Since the agricultural and industrial boom (more than 200 years ago), we have produced a huge amount of carbon dioxide and other greenhouse gases: the carbon dioxide concentration has risen by almost 30% (and is still rising by 0.4% annually), methane levels have more than doubled (a rise of 0.6% annually) and nitrous oxide levels are increasing as well (by 0.25% annually). All these are released primarily when we burn fossil fuels like coal, oil, petrol, natural gas and wood, as well. The natural way in which carbon dioxide is transferred back into oxygen is, being breath by green plants - mainly in rain forests. In the last few years, people have burned (and still are burning) huge areas of rain forest in the South America and central Africa for the purpose of agricultural aims. This means there are fewer threes, and of course, more carbon dioxide.
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