Montana Climate Matters
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The Sun is approximately 93 million miles from the Earth, yet we receive its warmth from the photons it sends across the void of space. We depend on Sun’s energy to survive, but currently our planet is warming too much.
Sunlight is a form of electromagnetic radiation. The Sun releases photons carrying electric and magnetic fields that oscillate. Our eyes have evolved to respond to oscillations between 430 trillion cycles per second at the red end of the spectrum and 750 trillion cycles per second at the violet end. Photon oscillations make the electrons of chemical bonds in the rods and cones of our eyes wiggle, sending a nerve impulse that our brain interprets as an image.
The frequencies of much incoming sunlight easily pass by gas molecules in the Earth’s atmosphere, mostly nitrogen (78%) and oxygen (21%). Some of the blue frequencies get scattered and color the sky blue to our eyes. Much potentially harmful ultraviolet frequencies do not reach us because the chemical bonds of ozone in the upper atmosphere absorb this shortwave radiation. This energy heats the ozone. In fact, atmospheric scientists define the stratosphere as the upper layer of the atmosphere in which temperatures rise with altitude instead of drop. Ozone’s filtering out of ultraviolet radiation allows life to exist on Earth.
Sunlight that passes through the ozone and reaches the Earth vibrates the chemical bonds of substances in the ground. Some of that energy is retained by the ground, making it warmer. Some is returned to the sky but its vibrational frequency is lowered. It is now in the electromagnetic region known as the infrared or longwave radiation. This radiation is detected as heat, not light.
Some re-emitted infrared radiation is absorbed by the chemical bonds of predominant gas molecules in the atmosphere, including nitrogen, oxygen, and water vapor. This, too, is part of the Sun’s warming of Earth and what we call the greenhouse effect. Historically, though, specific longwave frequencies were able to leak back into space because the molecules that could absorb them were not abundant in our atmosphere. For most of human history, the leakage rate was fairly constant, so our temperatures generally stayed on an even keel.
With the advent of the Industrial Revolution and growing populations, however, we have been altering the gas concentrations of the atmosphere. For example, levels of carbon dioxide have been steadily rising from about 285 parts per million in 1850 to 430 ppm at present. About three quarters of the rise has occurred since 1950 from the burning of fossil fuels and tropical deforestation. The chemical bonds of the increased carbon dioxide absorb specific frequencies of infrared radiation that once drifted back to space, heating our atmosphere to higher levels.
Infrared absorption is even more true with the bonds in methane gas emitted from livestock, fossil fuels, and landfill decomposition. Methane emissions have more than doubled in the past 200 years, which is worrying because it is 28 times more effective than carbon dioxide at trapping long-wave radiation and thus heat.
A third greenhouse gas is nitrous oxide. Recall our atmosphere is mainly nitrogen gas. When air is used as the source of oxygen for the combustion of fossil fuels such as gasoline or coal, nitrous oxide also forms. It also comes from nitrogen-based fertilizers and animal waste.
The ventilation holes—the transparent frequency bands that once allowed longwave radiation to escape from our atmospheric envelope—are becoming plugged. Until the release of greenhouse gases is curbed, our planet will continue to warm and we and our environment will suffer the consequences.
Garon Smith is Emeritus Professor of Chemistry from the University of Montana and former scientist on both the Missoula City-County Air Pollution Control Board and the Montana Board of Environmental Review.
