Climate change might be the most urgent issue of our day, both politically and in terms of life on Earth. There is mounting awareness that the global climate is a matter for public action.
For 11,500 years, atmospheric carbon dioxide (CO2) concentrations hovered around 280 ppm (the preindustrial “normal”), with an average surface temperature around 15°C. Since the Industrial Revolution, this level has been rising continuously, reaching 410 ppm in 2018. The geosciences, with their focus on timescales up to billions of years, are uniquely equipped to make extremely clear how abruptly industrial societies have changed and are changing the Earth’s climate.
Climate, greenhouse gases, CO2 and carbon sinks
The main engine of Earth’s climate is the sun. Our star delivers an average surface power of 342 W/m2 per year (roughly that of a hairdryer for each square meter of the planet). Earth absorbs about 70% of this and reflects the rest. If this were the only climate mechanism, the average temperature would be -15°C (below the freezing point of water, 0°C). Life would likely be impossible. Fortunately, some of the absorbed energy is re-emitted as infrared radiation, which, unlike visible light, interacts with the greenhouse gases (GHGs) present in the atmosphere to radiate heat back toward Earth’s surface. This greenhouse effect currently maintains our average temperature around 15°C.
The primary GHGs are water vapour and the much-debated CO2. Carbon dioxide contributes up to 30% of the total greenhouse effect, water vapour provides about 70%. CO2, though, has overall warming power that water vapour doesn’t. Water vapour in the atmosphere has a very short residence time (from hours to days) and its concentration can increase only if temperature increases. CO2 lingers in the atmosphere for 100 years and its concentration is not solely controlled by temperature. CO2 is thus able to trigger warming: if CO2 concentration increases, the average temperature, regardless of its own trend, will increase.
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