Climate change

Global warming

Global warming is undeniable and the changes of natural systems since the mid-1950s are unprecedented during the last millenia. Increase in air and ocean temperatures, ecosystem changes, melting of sea-ice and glaciers, rising sea levels, changes in migratory routes of birds and animals and acidification of the oceans are some of the serious consequences. The year 2016 was the warmest on record since the beginning of measurements and 2017 was the second warmest.

 

Global average surface temperature and concentration of carbon dioxide 1880–2010. The red and blue bars denote temperature above and below the average for the years 1901–2000, respectively. The brown bar signifies carbon dioxide in the air (measured in ppm). Source: NOAA/NCDC.

Global average surface temperature and concentration of carbon dioxide 18802010. The red and blue bars denote temperature above and below the average for the years 1901–2000, respectively. The brown bar signifies carbon dioxide in the air (measured in ppm). Source: NOAA/NCDC.

 

Concentration of carbon dioxide in the atmosphere measured at Stórhöfði Vestmannaeyjar islands. Source:http://brunnur.vedur.is/athuganir/efnavoktun/co2.html.

Concentration of carbon dioxide in the atmosphere measured at Stórhöfði Vestmannaeyjar islands. Source:http://brunnur.vedur.is/athuganir/efnavoktun/co2.html.

 

Since the industrial revolution, late in the 18th century, massive changes in human activities have led to greatly increased emissions of carbon dioxide (CO2)and other so-called greenhouse gases (GHGs), such as methane (CH4), into the atmosphere. This is the main cause of the current observed global warming, ocean acidification and associated consequences. The rapid increase in the concentration of CO2 and other GHGs in the atmosphere is mostly due to combustion of fossil fuels, such as coal and oil, in electric power plants, transportation and industry and a decrease in the uptake of carbon dioxide in vegetation, mainly due to deforestation, soil erosion, agriculture and expanding cities.

 

Reflection and absorption of solar radiation. Only 51% of the sunlight that hits the Earth is absorbed at the surface where it is used to heat the surface and lower atmosphere, melt ice and evaporate water, and to drive photosynthesis in plants. Approximately 26% of the radiation is scattered or reflected to space by clouds and atmospheric particles and 4% are reflected back to space by the Earth's surface. Atmospheric gases, particles and clouds absorb the remaining 19%. Source: physicalgeography.net.

Reflection and absorption of solar radiation. Only 51% of the sunlight that hits the Earth is absorbed at the surface where it is used to heat the surface and lower atmosphere, melt ice and evaporate water, and to drive photosynthesis in plants. Approximately 26% of the radiation is scattered or reflected to space by clouds and atmospheric particles and 4% are reflected back to space by the Earth's surface. Atmospheric gases, particles and clouds absorb the remaining 19%. Source: physicalgeography.net.

 

The nature of greenhouse gases

The effect of GHGs in the atmosphere has been well understood for decades. Both the Sun and the Earth emit electromagnetic radiation. GHGs in the atmosphere allow most of the high-energy radiation (short-wave radiation) from the Sun to pass through and reach the Earth’s surface. The Earth warms up as a result of the incoming radiation and reflects heat rays (long-wave infrared rays) back into the atmosphere. The GHGs in the atmosphere prevent this infrared radiation to pass through into space, but instead absorb the radiation and reemit part of it back to Earth. Thus, the GHGs function like a blanket. Hence, the mean temperature of the Earth is at present around 15°C, not –18°C as it would be without the atmosphere.

Many greenhouse gases, such as carbon dioxide, methane, water vapor, and nitrous oxide (N2O), occur naturally in the atmosphere. However, humans are altering their concentrations, especially the concentration of CO2, through interference with the carbon cycle (burning of forests, mining and burning of coal and oil). These activities artificially remove carbon from geological storage and convert it into its gaseous state, thereby increasing the atmospheric concentration of CO2. As a result, the concentration of CO2 (410 ppm in early 2018 but ca. 280 ppm before the industrial revolution)is higher now than at any other time during the last 650.000 years according to measurements of ice cores from Antarctica.

 

Comparison of atmospheric samples contained in ice cores and more recent direct measurements, provides evidence that atmospheric CO2 has increased since the industrial revolution. (Credit: Vostok ice core data/J.R. Petit et al.; NOAA Mauna Loa CO2 record). Source: https://climate.nasa.gov/evidence/

Comparison of atmospheric samples contained in ice cores and more recent direct measurements, provides evidence that atmospheric CO2 has increased since the industrial revolution. (Credit: Vostok ice core data/J.R. Petit et al.; NOAA Mauna Loa CO2 record). Source: https://climate.nasa.gov/evidence/

 

IPCC

The fifth scientific report of the Intergovernmental Panel on Climate Change (IPCC) of the United Nations was published in 2014. The IPCC reports are based on research by thousands of scientists and are the most comprehensive syntheses made about climate change. The results of the latest report confirmed and strengthened the findings of the 4th IPCC report from 2007, which marked a turning point in the global debate and awareness regarding climate change. The vast majority of climate scientists agree that the current global warming is mainly due to anthropogenic emissions of CO2.

Numerous studies published in peer-reviewed scientific journals show that the Earth’s climate is warming due to human activities. If the average increase in temperature exceeds 2°C, this will most likely lead to the collapse of many ecosystems on Earth and disasters for humankind. These findings prompted all nations of the world, except the US, to sign the Paris Agreement in 2015, whereby they pledge to keep global warming by 2100 below 2°C and preferably below 1.5°C.