Warming is Increasing Water Vapor’s Role as Our Most Abundant Greenhouse Gas, by Meteorologist Don Paul

Water vapor and global warming

In the last section of a recent Buffalo News article, I wrote that evidence of alarming increases in methane emissions from both human-made and natural activities appear to be establishing a feedback mechanism in which the methane-linked warming is probably increasing microbial methane emissions from warming sea beds, wetlands and melting permafrost, which, in turn, accelerate the ongoing warming.

A similar feedback mechanism appears to be underway in the relationship between atmospheric water vapor and global warming. Water vapor is, by far, the most abundant greenhouse gas in the atmosphere. Without greenhouse gases, according to NASA, Earth’s average surface temperature would be 59 degrees colder, and we wouldn’t be here.

What must be understood about water vapor is that in a stable climate, its abundance would be a constant, as would its greenhouse impact. It is part of the basic water cycle that makes life on Earth possible.

However, regular measurements taken by atmospheric scientists have detected what physicists would fully expect. Earth’s average temperature has gone up about 2 degrees Fahrenheit since the Industrial Revolution, due to the increases in carbon dioxide, methane, nitrous oxide and other greenhouse trace gases tied to human activity.

The human-made contributions to warming have destabilized the abundance of water vapor by warming waters and increasing evaporation. Warmer air can hold more water vapor, and so the amount of water vapor in the atmosphere is no longer a near constant. According to the laws of thermodynamics, for every degree Celsius the atmosphere warms, the amount of water vapor in it will increase by about 7%.

As NASA explains on the excellent website, climate.nasa.gov

, “It works like this: as greenhouse gases like carbon dioxide and methane increase, Earth’s temperature rises in response. This increases evaporation from both water and land areas. Because warmer air holds more moisture, its concentration of water vapor increases. Specifically, this happens because water vapor does not condense and precipitate out of the atmosphere as easily at higher temperatures. The water vapor then absorbs heat radiated from Earth and prevents it from escaping out to space. This further warms the atmosphere, resulting in even more water vapor in the atmosphere. This is what scientists call a ‘positive feedback loop.’ Scientists estimate this effect more than doubles the warming that would happen due to increasing carbon dioxide alone.”

Warming begets warming. It is now known human activity-linked greenhouse gases, especially carbon dioxide, are responsible for the warming climate. Global warming is accelerating the role of nature’s greenhouse gases by increasing their emissions from natural sources, which then increases their warming impacts. Our main hope is to globally broaden and speed reductions in carbon and methane emissions tied to fossil fuel extraction and burning as well as those produced by agriculture. Otherwise, these feedback mechanisms will only worsen and make the worst-case scenarios of a warming climate far more likely.