365 Days of Climate Awareness 3 - The Greenhouse Effect

365 Days of Climate Awareness  

3 - The Greenhouse Effect

Having jumped right into some minutiae of modeling, perhaps I should step back and address a few basics of climate change science, all the more since these are terms which are popularly known but perhaps not as well understood. First up: the greenhouse effect.

The Sun emits radiation constantly, because of the hydrogen fusion happening within it. This radiation ranges from infrared through visible light up to ultraviolet. The ocean and land absorb ultraviolet and infrared and so gain heat. But the land re-radiates some of its heat as infrared, long-wave, radiation.

It's this outgoing IR radiation which is absorbed by what's known as the greenhouse gases. After absorbing the outgoing heat radiation, the gas molecules re-radiate it in all directions, sending a portion back down to the planet surface. In this way, greenhouse gases--so named for this reason--form an insulating layer around the planet. An increase in the concentration of greenhouse gases leads to increased heat content around the globe.

A list of the major types: carbon dioxide (CO₂); methane (CH₄); water vapor (H₂O); nitrous oxide (N₂O); ozone (O₃); chlorofluorocarbons; pefluorocarbons; sulfur hexafluoride (SF₆).

The greenhouse effect was first identified by John Tyndall in 1859, in a series of experiments with carbon dioxide and water vapor. In the late 1800's Svante Arrhenius estimated the effect of varying concentrations of carbon dioxide on the global climate. That was the foundation for our modern understanding the influence of carbon dioxide and other gases on climate.

Without any greenhouse gases in the atmosphere, it's estimated that global average temperature would be 0 degrees Fahrenheit, instead of the current average of 47. The greenhouse effect is vital to life as we know it on earth.

Back briefly to the Sun: it emits radiation reasonably steadily (on a roughly 11-year sunspot rhythm). On average, 341.3 watts per square meter of heat radiation reach the top of Earth's atmosphere. With the Sun's output so steady, changes in Earth's heat content are a matter of changes in atmospheric insulation.

Next up: weather versus climate.

Be well!