It’s physics: Carbon dioxide and climate change

Ever wonder why your feet burn when you walk on a dark asphalt road on a hot and sunny summer day, but they’re just fine when you’re standing on grass? That’s because, in comparison to grass, asphalt absorbs far more heat than it reflects, which raises the temperature of the surface of the road.

Physics lesson 1: All other conditions being the same, the more heat that a substance is able to absorb, the hotter it becomes. It’s physics but also common sense.

As afternoon turns to evening and night, that asphalt road, and anything else that has been heated by the sun, cools after sunset as the earth sends, or re-emits, this heat back into cooler space.

The scientific work of John Tyndall in the 1860s and 1870s showed how certain gases absorb far more heat than other gases.  We now know that carbon dioxide is one such greenhouse gas present in the earth’s atmosphere.


John Tyndall, On Radiation Through The Earth’s Atmosphere, Public lecture, January 1863.

As the nighttime heat re-emitted by the earth passes through the atmosphere, some of it is absorbed by carbon dioxide. This absorbed heat is then re-emitted back to earth and also outwardly to space.

If carbon dioxide and other greenhouse gases, such as water vapour, had not been present in the earth’s atmosphere, all of the re-emitted heat from the earth would have escaped back to space. With the intervention of greenhouse gases, some of this heat is instead returned to the earth’s surface, where it is absorbed.

Consider this to be a simple math addition problem. The additional heat absorbed by the earth warms our planet, which is referred to as the greenhouse effect. If there were no greenhouse gases in the atmosphere, we would have a chilly and inhospitable earth. The flip side is that any further addition of carbon dioxide to the atmosphere increases the overall influence of greenhouse gases, making our planet warmer.

Such a warming has occurred gradually since John Tyndall’s time when the Industrial Revolution had just begun. Over the intervening period, carbon dioxide levels in the atmosphere have increased from 280 to 400 parts per million.  The fraction of carbon dioxide in the atmosphere is at its highest level in the past 80,000 years for which data are available.

The increase strongly correlates with the burning of fossil fuels after the Industrial Revolution. More carbon dioxide is produced today through human activities than was emitted two centuries ago.

Physics lesson 2: The more greenhouse gases we add to our earth’s atmosphere the more our planet will warm.

Scott Pruitt is the new Administrator of the U.S. Environmental Protection Agency. In a recent interview with CNBC, he said that he was not convinced that carbon dioxide pollution from burning fossil fuels like oil, gas and coal is the main cause of climate change.

The use of fossil fuels to provide energy and create materials is ubiquitous. Depending on perspective and ideology, it is possible to debate the social injury that fossil fuels cause against the immediate social benefits that they provide.

However, because of physics, the influence of increasing greenhouse gases on global warming and climate change is indisputable. (See physics lessons 1 and 2 above.)

The lack of understanding of physics occurs more frequently than one might think. The NBA player Kyrie Irving recently claimed that the earth is flat. It isn’t.

Neil deGrasse Tyson, named one of ten most influential people in science by Discover magazine in 2008, implored Mr. Irving to stick to basketball with a fitting response, “… if you have certain limitations of understanding of the natural world, stay away from jobs that require that.”

Extra credit for more scientifically minded readers: Read this seminal scientific paper describing the effect of increasing carbon dioxide in the atmosphere on global warming.
Hansen, J.D. JohnsonA. LacisS. LebedeffP. LeeD. Rind, and G. Russell, 1981: Climate impact of increasing atmospheric carbon dioxideScience213, 957-966, doi:10.1126/science.213.4511.957.


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