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Science of Global Warming

The Basic Science of Global Warming

In 1824, a scientist named Joseph Fourier asked a question: why is Earth warmer than it should be if it were exposed to space? The answer, as he would come to recognize, is our atmosphere. While the term did not exist at the time, Fourier was the first to describe what we know today as the greenhouse effect.

The Greenhouse Effect

So what is the greenhouse effect? The Earth receives energy from the Sun through various forms of radiation: visible light, near infrared, and ultraviolet. Some of it either bounces off or is absorbed by the atmosphere, but much of it reaches the planet. The energy heats the planet, which in turn emits radiant heat back toward space. The atmosphere absorbs the outgoing infrared radiation and re-emits radiation in all directions warming both the atmosphere and the Earth’s surface.

Nearly 30 years later, a scientist named John Tyndall became the first to demonstrate the greenhouse effect through experimentation. Using techniques that measure the absorption of radiation, Tyndall demonstrated that water vapor absorbs radiant heat. He would go on to quantify the absorption capacity of carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and ozone (O3). We know them today as the primary greenhouse gases.

The tiny amount of physics we just covered is the core science of global warming. That’s it. It’s a simple equation: an increase in greenhouse gas means an increase in energy trapped below. Global warming is first and foremost a consequence of the laws of nature. We live in a giant greenhouse.

Carbon Dioxide – On the Way Up

We now know that carbon dioxide is a potent greenhouse gas and that it plays an important part in regulating temperature on planet Earth. For hundreds of thousands of years, the amount of carbon dioxide in the atmosphere has cycled up and cycled down as the Earth transitioned from ice age to interglacial period and back again. Ice ages occur due to changes in Earth’s orbit around the Sun known as the Milankovitch Cycle.

Carbon Dioxide Measurements Over Time

Knowing the natural variations of carbon dioxide within Earth’s climate cycles is important because it allows us to accurately analyze the uncharacteristic increase that coincides with carbon-based energy production. Again, we are taken back to the simple equation we mentioned earlier: more greenhouse gas in the atmosphere means more energy trapped in the system.

Editor’s Note: Serbian astronomer Milutin Milanković theorized that minute changes in the Earth’s orbit around the Sun (eccentricity, axial tilt, and precession) due to gravitational influences would affect the climate on Earth through orbital forcing. In other words, gravity caused slight changes in Earth’s movement around the Sun that resulted in changes in solar radiation hitting the planet. In 1976, scientists confirmed Milutin’s theory through observation of various paleoclimate proxies (deep ocean cores). The cycle happens over 10s of thousands of years and we know it today as the Milankovitch Cycle.

Global Warming or Climate Change – What’s in a Name?

For many the words are used interchangeably, but that is unfortunately a product of misunderstanding in common language terminology. In a scientific sense they refer to two distinct, yet related occurrences. Global warming is the incremental increase in the average temperature of the Earth, which includes the oceans, the planet surface, and the various layers of the atmosphere. Climate change refers to the effects on regional climates around the world as they respond to the increased energy in the climate system. Much of the current scientific research revolves around monitoring and studying various climates to measure and project potential changes. In short, global warming causes climates to change.

Photo Credit: NASA