For hundreds of thousands of years, prior to the industrial revolution, CO2 the principal greenhouse gas that holds heat in our atmosphere never rose above 300 ppm. The last time Earth's CO2 was 400 ppm was during the Pliocene era, some 3 million years ago, when sea levels were 49 to 82 feet higher.
Because of the higher level of greenhouse gases, average global temperatures have risen 1.4 degrees Fahrenheit over the past century. That seemingly small increase in temperature is already showing up in the form of more prolonged droughts that reduce crop yields, wildfires that are intensified by drier conditions, and storms like Sandy becoming more frequent and destructive.
The effects we're seeing now are a small taste of what's in store if we let the Keeling Curve, as it is known, continue along its current trajectory and temperatures climb 7 degrees or more by the end of the century. Such a scenario would cause food shortages resulting in mass starvation and higher sea levels that would displace hundreds of millions of people. Large swaths of populated areas would be too hot for humans to tolerate.
While I'm on the subject of numbers, there's another one equally as important as 400 ppm. Actually, it's a ratio: 1000 to 1. That's the amount of certainty among scientists who do peer-reviewed research that climate change is happening and that human activity is the primary driver.
Jim Powell, a science author who served 12 years on the National Science Board, conducted a study of nearly 13,950 peer-reviewed climate articles published between 1991 and 2012. Only 24 of those articles "clearly reject global warming or endorse a cause other than CO2 emissions for observed warming."
The articles Powell reviewed were written by a total of 33,690 authors. The 24 rejecting articles were written by 34 authors (about 1000 to 1).
Despite this overwhelming consensus, climate change skeptics have flim-flammed the media, public and elected officials into believing a debate actually exists among climate scientists on this issue. This perception of uncertainty, driven by those who have a vested interest in maintaining the status quo, contributes significantly to the paralysis surrounding effective solutions to climate change.
As Powell so aptly put it, "Scientists do not disagree about human-caused global warming. It is the ruling paradigm of climate science, in the same way that plate tectonics is the ruling paradigm of geology. We know that continents move. We know that the earth is warming and that human emissions of greenhouse gases are the primary cause. These are known facts about which virtually all publishing scientists agree."
Having surpassed 400 ppm of CO2, there is uncertainty only on these points: How bad will things get? How quickly will it happen?
If we take steps now to reduce our CO2 emissions, there's a good chance we can adapt to the changes that are coming. A revenue-neutral carbon tax, with proceeds returned to consumers, would be an important first step toward restoring the balance that nature maintained since the dawn of civilization.
These are the numbers 400 ppm and 1000 to 1 that are screaming at us: Stop burning that stuff!
Mark Reynolds is executive director of Citizens Climate Lobby in Coronado, Calif.