The Greenhouse effect makes our planet habitable. Without it the average temperature on Earth’s surface would be about −18°C, not the pleasant 15°C we currently have. As depicted in this NASA video, greenhouse gases in the atmosphere absorb heat and reflect it back in all direction, warming the Earth. This process is called the Greenhouse Effect.
Greenhouse gases (GHGs)
Water vapor, Carbon dioxide (CO2), methane(CH4), Nitrous oxide(N2O) and man made fluorinated gases Chlorofluorocarbons (CFCs) and Hydrochlorofluorocarbons (HCFCs) are all greenhouse gases. Once released in the atmosphere each of them has a different lifetime and a different Global Warming Potential (GWP).
According to the IPCC(Intergovernmental Panel on climate change) “Radiative forcing is a measure of the influence a factor has in altering the balance of incoming and outgoing energy in the Earth-atmosphere system and is an index of the importance of the factor as a potential climate change mechanism. In this report radiative forcing values are for changes relative to preindustrial conditions defined at 1750 and are expressed in Watts per square meter (W/m2).”
Rise of the amount of GHGs in the atmosphere
In the past 400,000 years, during ice ages, CO2 levels were around 200 parts per million (ppm), and during the warmer interglacial periods, they hovered around 280 ppm (see fluctuations in the graph). Before the Industrial Revolution in the 19th century, global average carbon dioxide was about 280 ppm. In May 2019 sensors in Hawaii recorded Earth’s atmospheric concentration of carbon dioxide (CO2) passing 415 ppm for the first time since before the ancient dawn of humanity.
Not only CO2 emissions have risen in the last centuries. The amount of other greenhouse gases like Methane, Nitrous oxide and man made fluorinated gases has also increased in the atmosphere.
Human activities are the main reason why the amounts of greenhouse gases in the atmosphere have increased in the last centuries.