365 Days of Climate Awareness 5 - Greenhouse gases

365 Days of Climate Awareness  

5 - Greenhouse gases

The three most important greenhouse gases are carbon dioxide, methane, and water vapor. There is a handful of far more powerful, but fortunately more rare, chemicals which likewise trap heat and warm the planet. This is a brief summary.

Carbon dioxide (CO₂): The dominant greenhouse gas, with a much greater effect than the next most important, methane. CO₂ is produced by many forms of oxidation of carbon-based matter: burning wood, oil, gas or coal; and by respiration within our own cells. CO₂ is in turn consumed by plants during photosynthesis (though those same plants do then release some CO₂ again with their own cellular respiration). The concentration of CO₂ is currently 410 ppm (parts per million), and was 240 ppm before the industrial revolution. Carbon dioxide has been far from the only influence on earth's climate throughout the planet's 4.7 billion-year existence, but its role is significant.

Methane (CH₄): Methane is up to 100 times as effective as CO₂ in trapping and re-radiating IR energy, but its role is still smaller because its concentration is far lower (1500 parts per billion--ppb--up from 750 ppb before the industrial era), and because it tends to remain in the atmosphere for 100 years before descending back to the ground, as opposed to CO₂, which resides there for over 1000 years. Methane comes from a number of sources, including agriculture, oil and gas production, outgassing from decomposing materials (including human dumps), and other natural sources like permafrost melting (accelerating now with a warming planet).

Water vapor (H₂O): a powerful greenhouse gas in its own right, and a natural part of our weather as part of the worldwide water cycle. An increasingly warm planet means more water content in the atmosphere, increasing water vapor's warming potency. However, more vapor also leads to more clouds, which help block incoming UV radiation, a negative feedback.

Nitrous oxide (N₂O): Even more potent than methane, being about 114 times as effective as CO₂ in trapping heat, and remains in the atmosphere for over 100 years before disintegrating. Its main sources are agriculture, industry and energy production. Historically N₂O concentration has hovered around 265 ppb, but during the industrial era has increased quickly to 335 ppb.

Ozone (O₃): In the stratosphere (30-50 km altitude), ozone blocks UV radiation and so helps cool the planet and make it livable. It forms by chemical breakdown of breathable oxygen (O₂) via the sun's radiation. But closer to the ground, ozone is produced by combustion and is a pollutant, among other things, insulating the planet much like CO₂ does. Ozone is not a well-mixed atmospheric gas, constantly being made and breaking down, varying with time and distance.

Chlorofluorocarbons & perfluorocarbons: a number of gases (including the CFCs which were destroying the ozone layer in much of the 20th century) produced industrially. They can be hundreds of times more potent than CO₂ as insulators, but in concentrations generally measured in the parts per trillion (ppt) and with shorter atmospheric residence times.

Sulfur hexafluoride (SF₆): A frighteningly effective greenhouse gas--nearly 23,000 times as effective as CO₂, and highly stable chemically--produced industrially and with a number of applications in electronics. Its current atmospheric concentration is roughly 2.5 ppt.

Tomorrow: albedo.

Be well!