Global warming
Global warming refers to the recent (pre-industrial – present) increase in the average temperature of the Earth’s surface and lower atmosphere. Although there used to be some controversy on the actual impacts of humans, scientists are now more than 90% sure that it is primarily caused by increasing concentrations of GHGs produced by human activities, which intensify the natural greenhouse effect.
Since the Industrial Revolution (around 1750), human activities have been emitting CO2 and other greenhouse gases (GHGs) on a large scale, primarily through the burning of fossil fuels and clearing of forests. Although the quantity of CO2 emissions resulting from these activities is small compared with those in the natural carbon cycle, these additional quantities are not completely recycled by ecosystems. Instead, they accumulate with the existing gases in the atmosphere, leading to rising concentrations of GHGs. For instance, the atmospheric concentration of CO2 alone has already increased by over 40% since the Industrial Revolution, and the Intergovernmental Panel on Climate Change (IPCC) predicts that this concentration could triple by 2100 if no action is taken.
Source: http://www.c2es.org/facts-figures/trends/long-co2-temp
This increase in heat-trapping GHGs causes an imbalance in the radiation balance of the Earth: since more outgoing IR radiation is trapped, the Earth will receive more radiation from the sun than it is emitting to space, causing the Earth to warm until there will be again a balance in incoming and outgoing radiation. Using the blanket analogy, the more GHGs we emit, the thicker the blanket becomes and the warmer the Earth will become.
According to the IPCC, warming of the climate system is unequivocal, as is evident from observations of increases in global average air and ocean temperatures, the widespread melting of snow and ice and rising global average sea levels. Over the past 100 years, the temperature on the Earth’s surface has already increased by 0.8 °C, while 0.6 °C of this warming took place in the last three decades. As we continue emitting GHGs, this rise is expected to continue.
It should be noted that the average temperature of the Earth’s surface and lower atmosphere has been going up and down continuously throughout the history of the Earth as a result of natural climate variability. However, many experts are worried because the current rate of global warming is much greater than the usual warming rate of such changes in the past. This could lead to some very serious consequences.
Sources:
Intergovernmental Panel of Climate Change (2007). Climate Change 2007: Synthesis Report. Contribution of Working Groups I, II and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, Pachauri, R.K and Reisinger, A. (eds.)]. IPCC, Geneva, Switzerland, 104 pp. Available on: http://www.ipcc.ch/publications_and_data/ar4/syr/en/contents.html
National Research Council (2011). America's Climate Choices. The National Academies Press, Washington DC, USA, 118 pp. Available on: http://www.nap.edu/openbook.php?record_id=12781&page=R1
This increase in heat-trapping GHGs causes an imbalance in the radiation balance of the Earth: since more outgoing IR radiation is trapped, the Earth will receive more radiation from the sun than it is emitting to space, causing the Earth to warm until there will be again a balance in incoming and outgoing radiation. Using the blanket analogy, the more GHGs we emit, the thicker the blanket becomes and the warmer the Earth will become.
According to the IPCC, warming of the climate system is unequivocal, as is evident from observations of increases in global average air and ocean temperatures, the widespread melting of snow and ice and rising global average sea levels. Over the past 100 years, the temperature on the Earth’s surface has already increased by 0.8 °C, while 0.6 °C of this warming took place in the last three decades. As we continue emitting GHGs, this rise is expected to continue.
It should be noted that the average temperature of the Earth’s surface and lower atmosphere has been going up and down continuously throughout the history of the Earth as a result of natural climate variability. However, many experts are worried because the current rate of global warming is much greater than the usual warming rate of such changes in the past. This could lead to some very serious consequences.
Sources:
Intergovernmental Panel of Climate Change (2007). Climate Change 2007: Synthesis Report. Contribution of Working Groups I, II and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, Pachauri, R.K and Reisinger, A. (eds.)]. IPCC, Geneva, Switzerland, 104 pp. Available on: http://www.ipcc.ch/publications_and_data/ar4/syr/en/contents.html
National Research Council (2011). America's Climate Choices. The National Academies Press, Washington DC, USA, 118 pp. Available on: http://www.nap.edu/openbook.php?record_id=12781&page=R1
