• Raul Augusto Zenon

It’s Water Vapor, Not the CO2

Its widely spread and accepted, as being an axiom, that the main issue regarding increasing average temperatures and climate change is the growing concentration of CO2 in the upper atmosphere. However, you may be amazed that this non-condensable greenhouse gas contribution is actually, marginal. In plain English, forget the CO2! Water vapour is the most important greenhouse gas. It controls Earth’s temperature.

Water vapour is indeed the largest contributor to the Earth’s greenhouse effect. On average, it probably accounts for about 60% of the warming effect. However, water vapour does not control the Earth’s temperature but is instead controlled by the temperature. This is because the temperature of the surrounding atmosphere limits the maximum amount of water vapour the atmosphere can contain. If a volume of air contains its maximum amount of water vapour and the temperature is decreased, some of the water vapour will condense to form liquid water. This is why clouds form as warm air containing water vapour rises and cools at higher altitudes where the water condenses to the tiny droplets that make up clouds.

The greenhouse effect that has maintained the Earth’s temperature at a level warm enough for human civilization to develop over the past several millennia is controlled by non-condensable gases, mainly carbon dioxide, CO2, with smaller contributions from methane, CH4, nitrous oxide, N2O, and ozone, O3. Since the middle of the 20th century, small amounts of man-made gases, mostly chlorine- and fluorine-containing solvents and refrigerants, have been added to the mix. Because these gases are not condensable at atmospheric temperatures and pressures, the atmosphere can pack in much more of these gases. Thus, CO2 (as well as CH4, N2O, and O3) has been building up in the atmosphere since the Industrial Revolution when we began burning large amounts of fossil fuel and heavy tillage from agricultural development began releasing carbon stored in the ground by microbes.

If there had been no increase in the amounts of non-condensable greenhouse gases, the amount of water vapour in the atmosphere would not have changed with all other variables remaining the same. The addition of the non-condensable gases causes the temperature to increase leading to an increase in water vapour that further increases the temperature. This is an example of a positive feedback effect. The warming due to increasing non-condensable gases causes more water vapour to enter the atmosphere, which adds to the effect of the non-condensables.

There is also a possibility that adding more water vapour to the atmosphere could produce a negative feedback effect. This could happen if more water vapour leads to more cloud formation. Clouds reflect sunlight and reduce the amount of energy that reaches the Earth’s surface to warm it. If the amount of solar warming decreases, then the temperature of the Earth would decrease. In that case, the effect of adding more water vapour would be cooling rather than warming. But cloud cover does mean more condensed water in the atmosphere, making for a stronger greenhouse effect than non-condensed water vapour alone – it is warmer on a cloudy winter day than on a clear one. Thus the possible positive and negative feedbacks associated with increased water vapour and cloud formation can cancel one another out and complicate matters. The actual balance between them is an active area of climate science research.

Now, the question is, are we really impeding the water to cycle naturally as it should be? Indeed we are! As mentioned, by heavy tillage practices and herbicides intensive use, large areas of agricultural land remain uncovered (without any plants growing) during considerable periods during the year. As it may sound obvious, bare soil exposed to sun radiation increases its temperature to a point where the underground humidity starts to quickly evaporate. The effect is magnified and accelerated by heavy tillage where the soil exposed surface area is increased. In many parts of the world, we can observe desert-like environments where nothing could grow without the use of chemical and synthetic inputs. This should not be, by any mean, the way we grow our food.

In the following posts, we will continue demystifying, common beliefs about climate change, agricultural practices and sustainability under the light of regenerative agriculture.

Best Wishes!

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