N2, O2, Ar, and then greenhouse gases H2O, CO2, and trace greenhouse gases CH4, N2O, O3 and SO2, and then smaller amounts of CFCs, HFCs, HCFCs, and the like, and then even smaller amounts of species such as SF6. If we want to understand global warming, we really need to understand the role of these gases in our atmosphere and how they can affect climate.
Global warming has one underlying cause: man-made emissions of greenhouse gases. Yes, there are some natural processes, such as forest fires and volcanic eruptions that can influence warming, but not to the same extent as anthropogenic sources of greenhouse gases.
Don't let your crazy uncle convince you otherwise.
The greenhouse gases in the atmosphere are those that are transparent to visible light - letting sunlight through to hit the earth's surface - but which absorb infrared (IR) emissions from the earth's surface.
Most of the atmosphere is transparent to IR. Dry air is composed of 99.96% non-greenhouse gases. The leading greenhouse gas in the atmosphere is water vapor, but water vapor in the air has a temperature-dependent upper limit - its equilibrium vapor pressure; increasing water vapor above its equilibrium vapor pressure leads to precipitation of either liquid or solid water, that is, rain or snow, depending on the temperature.
Consider these aspects of water. Suppose that you took all of the H2 on the planet and burnt it. The only significant product of H2 combustion is water vapor, so the vapor pressure of water would increase, and increase, and increase - until it hit the equilibrium vapor pressure, at which point it would rain or snow - a phenomenon very well known in the Pacific Northwest.
If you didn't want to burn H2, how would you increase the amount of water vapor in the air? Easy - warm up some water. The oceans are a convenient source. Warming the globe's surface waters is a sure-fire [OG - forgive the pun] way to get more H2O into the atmosphere.
For these reasons, H2O(g) is regarded as a response to global warming, not a driver. One could argue that condensing water vapor into clouds will increase the albedo of the earth, reducing solar insolation at the earth's surface, and lead to global cooling. While the scientific jury is still out on this question, there is increasing evidence that warming waters lead to reduced cloud cover, not an increase. We will discuss this in the last post in this series.
The leading non-condensing greenhouse gas in the atmosphere is CO2. It is not a minor species; it is the most significant non-condensing greenhouse gas in our atmosphere. Don't let your crazy uncle convince you otherwise.
Here's NASA:
This absorption and radiation of heat by the atmosphere—the natural greenhouse effect—is beneficial for life on Earth. If there were no greenhouse effect, the Earth’s average surface temperature would be a very chilly -18°C (0°F) instead of the comfortable 15°C (59°F) that it is today.
Some minor species!
From Wikipedia:
As of 2023, by mole fraction (i.e., by number of molecules), dry air contains 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.04% carbon dioxide, and small amounts of other gases. Air also contains a variable amount of water vapor, on average around 1% at sea level, and 0.4% over the entire atmosphere.
What happens when we have too much carbon dioxide?
From climate.gov:
Scientists say that doubling pre-industrial carbon dioxide levels will likely cause global average surface temperature to rise between 1.5° and 4.5° Celsius (2.7° to 8.1° Fahrenheit) compared to pre-industrial temperatures. (Current concentrations are about 1.4 times pre-industrial levels.) The full process could take hundreds of years—perhaps more than a thousand—to play out. Climate scientists call the full temperature rise from doubled carbon dioxide concentrations the equilibrium climate sensitivity.
To understand how sensitive the climate is to carbon dioxide on time frames of a century or less, scientists also study the transient climate sensitivity. They imagine that carbon dioxide will continue to increase at roughly the rate it has been, and then ask how much warming would be realized around the time when the concentration has doubled the preindustrial value. On this shorter time scale, it’s likely the planet will warm between 1° and 2.5°C (2°-4.5°F).
That is the essence of the problem: How soon will the increase in greenhouse gases make the planet too hot?
Note: All calculations were performed within Mathematica Home Edition 13.2.1.0. on a MacBook Pro with macOS Sonoma 14.5. A PDF of the original Mathematica output is available upon request to Jim Diamond, jimd at Linfield dot edu.
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