Over the last few months, I’ve received emails and Facebook postings asking about reports of colder than typical temperatures in the thermosphere, the very top level of our atmosphere, over the past few years according to NASA and other agencies and universities.
More importantly, is this is an indication that global warming has diminished or even stopped?
I wish it were, but unfortunately, the historical and current oceanographic and atmospheric data along with future numerical climate model projections clearly say otherwise. Here’s why.
In Greek mythology, Daedalus constructs a set of wings for his son Icarus made from feathers and wax to escape from Crete. Daedalus warns his son not to fly too low nor too high, so wetness of the Mediterranean Sea would not dampen his wings, or the sun’s heat melts them away.
Regrettably, Icarus ignored his father’s advice and flew too close to the sun. As the tale goes, the sun’s heat melts the wax that held the feathers in place and gravity pulls the featherless Icarus into the sea.
This fable reminds me of the layers of the atmosphere.
The troposphere is the lowest layer of our atmosphere, which starts at sea level and extends upward to approximately 33,000 feet, depending on your latitude and the atmospheric conditions; some days, this level can be higher other days lower. Excluding inversion layers, as you climb higher in the troposphere, temperatures decrease with the lower air pressure. Pretty much all the weather we experience on earth occurs in the troposphere, which contains approximately 99 percent of the atmosphere’s water vapor.
On top of the troposphere is the stratosphere, which extends to around 160,000 feet above the ground. The ozone layer, which absorbs significant amounts of the ultraviolet (UV) light from the sun and converts much of it to heat, is in the stratosphere. In other words, in this layer, the higher you go, the warmer it gets. Perhaps that’s why Icarus’ wings melted. The air is thin at these altitudes; consequently, the atmosphere is stable, which produces a smooth ride for jet airliners.
Above the stratosphere is the mesosphere where temperature, like in the troposphere, decreases with height, dropping to around 130 degrees below zero Fahrenheit.
The thermosphere lies above the mesopause and ranges between about 200,000 to over 1,000,000 feet above the earth’s surface. Here, the temperatures increase with height. This warming is caused by the absorption of considerable amounts of radiation in the higher frequencies of the electromagnetic spectrum from the sun, like UV light, x-rays and maybe even a few gamma rays.
Higher amounts of this type of radiation are associated with sunspots and solar flares. However, the sun is currently at its solar minimum, the period of least solar activity. In other words, we are presently seeing the lowest sunspot counts in the 11-year solar cycle.
This explains why temperatures in the thermosphere have been cooling, but there could be another kind of force taking place in this region partially responsible for the chillier temperatures, and it’s called the “greenhouse” effect.
For hundreds of thousands of years, carbon dioxide (CO2) levels have remained below 300 parts per million (ppm). We precisely know the historical levels of CO2 from the analysis of air bubbles trapped in the ancient ice from Antarctica and Greenland. However, since the Industrial Revolution in the late 18th century, CO2 levels have dramatically increased, and hit nearly 416 ppm in May at Scripps and the Mauna Loa Observatory.
The air we breathe in the lower levels of our atmosphere is mostly made of approximately 78 percent nitrogen (N2) and 21 percent oxygen (O2), which are symmetrical molecules with only two atoms. Some of the other gases we breath are CO2 (one atom of carbon and two of oxygen) and water vapor (H2O: two atoms of hydrogen and one of oxygen). These molecules are not symmetrical, and they actively interact with the sun’s rays, like infrared radiation and even some visible light converting them into heat.
Way back in the 1850s, Irish physicist John Tyndall documented these interactions.
Just like closing the windows of a car on a sunny day, more of the sun’s radiation is converted to heat in the troposphere at the earth’s surface with less of the sun’s energy reflected back to space through the thermosphere, thus perhaps helping to produce cooler temperatures in that region of the sky. Increasing amounts of greenhouse gases are disrupting the equilibrium level between incoming and outgoing energy from the sun, producing warmer temperatures in the oceans and troposphere.
As the climate continues to warm, ensure that your family knows what to do when extreme weather, natural disasters, or other dangerous events occur. Such events can happen quickly and catch you off guard. Make it a priority to create an emergency plan today. Please visit www.pge.com for information.