Aren’t human emissions of CO2 a fraction of those from natural sources?
Absolutely. Emissions of CO2 from human sources are dwarfed many times over by emissions of the gas from natural sources. However, it is the human emissions that are throwing off the balance. Take mankind out of the equation, and the Earth’s climate reaches a balance between forcings and effects. Natural climate forcings can be anything from variations in solar output to volcanic and tectonic activity to changes in the Earth’s orbit around the Sun. The Earth adapts to these natural forcings by changing aspects of its biosphere including temperature, ice coverage, ocean alkalinity, and so on. As these natural forcings proceed through cycles, so does the Earth’s climate, going back and forth between colder and milder climates, denser and thinner atmospheric coverage, and so on, constantly reacting to these natural influences. However, the emission of greenhouse gases by mankind is creating its own forcing on the Earth’s climate.
Imagine an immense scale. On one side you have Earth’s natural forcings, including natural emissions of greenhouse gases like CO2. On the other is the Earth’s reactions. As the forcings change, causing the scale to tip, the reactions change to match, constantly striving to reach a balance. Generally speaking, these natural forcings, and the Earth’s reactions, change over the course of thousands of years. So, at any given moment in time, the scale is pretty much in balance.
Now imagine that mankind adds a small weight to the forcings side. It’s tiny, miniscule in comparison to the natural forcings. As you might expect, the Earth’s reaction is not even noticeable. However, CO2 can remain in the atmosphere for upwards of a hundred years. So, the next year, mankind adds another small weight, this one slightly larger than the previous, to the forcings side, adding to the weight previously added by mankind. Once again, the Earth’s reactions are negligible. But, mankind keeps it up. Each year, a new weight is added, each one larger than the previous, and this process is continued with up to 100 years passing before that first weight is removed.
As you can imagine, after a while, the Earth’s reactions to these added weights is no longer indiscernible. The climate’s temperature goes up. The Earth gets more humid as water vapor is added to the atmosphere. Glaciers melt and recede. The ocean’s alkalinity changes. Coral reefs die. Ocean temperatures rise. All of the things we are seeing happening to the world around us. The Earth is trying to regain its balance.
However, in contrast to natural influences, mankind’s influence is not cyclical. Unless we actively do something to change it, mankind will continue to add more and more weight to the scale, and the Earth will continue to react. And Mother Nature doesn’t care whether her reactions are beneficial to mankind or not.