Background: Climate Change

Earth’s climate has gone through many changes.

Earth’s first atmosphere, before life emerged, was created by off-gassing from cooling rocks. It had no oxygen. Once single-cell life started in the ocean, oxygen started collecting in the atmosphere. After a while some of that oxygen split into ozone and collected in the upper  atmosphere. That ozone layer blocked enough of the ultraviolet light that life could live on land, as well as in water. Animal life grew to take advantage of the oxygen accumulating in the atmosphere from plant life,  taking the oxygen in and breathing out carbon dioxide (CO2). The basic atmospheric components we are familiar with were then complete: the balance of oxygen, CO2, ozone, and other trace elements was sufficient to trap heat in the air and maintain a temperature conducive to the spread of life.

Temperatures and CO2 levels are particularly closely linked. Rising temperatures cause the release of CO2 that tends to be trapped in ice, permafrost, and the oceans. Increased CO2 levels cause an increase in temperatures by creating a thicker heat-absorbing “blanket” in the atmosphere — the greenhouse effect.

On geological time scales, and before humans came along, there have been major-though-slow shifts in both the Earth and the sun that have made temperature and CO2 levels rise and fall. These variations have been driven mostly by changes in the amount of sunlight hitting the earth’s surface because of periodic variations in Earth’s orbit called Milankovich Cycles. Here’s a chart showing those rises and falls in the Earth’s  CO2  and temperature. Each period of change is initiated by the changes in Earth’s orbit, and then CO2 and temperature push each other up or down. CO2 generally stayed between 180 and 320 parts per million (ppm) until emissions related to the Industrial Revolution began to heat things up.


During this whole time, some carbon-rich plant life was being buried under the surface. Some of that plant life, depending on the geological history around it, became one of the “fossil fuels”: coal, crude oil, or methane (“natural gas”).

Each fossil fuel, as it was recovered by humans in large quantities, transformed human civilization through the energy that was released by burning it. This technological revolution made (and continues to make) some people quite rich, raised the standard of living for many, and generally harmed only those who lived near extraction sites, or downwind of where the fuel was burned.

But when human civilization began to reach a critical size and velocity of expansion, the burning of those fossil fuels started changing the composition of the atmosphere, and thus the global average temperature. If we zoom in to that chart to focus on the last 100+ years, we see rapidly rising temperatures beginning especially around 1980:

Atmospheric carbon dioxide concentrations and global annual average temperatures over the years 1880 to 2009

We are entering unknown territory, with CO2 levels breaking through and beyond 400 ppm. Temperatures are beginning to respond, but there is a lag time, and we have already “baked in” a lot of temperature rise. The climate system is complex enough that scientists are still working out where the “tipping points” are. When will positive feedback loops that act to accelerate climate change overcome the negative feedback loops that tend to keep it in check? We don’t know yet, and we don’t want to find out by hitting them.

The climate change challenge for all of humanity is to reduce or eliminate our use of fossil fuels as quickly as possible, to keep future climate change to a livable minimum.

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