For the first time in human history, hourly global warming being a reality. However, without some background information about the keeling curve and parts per million it can be difficult to recognize just how important this benchmark is to our planet.
What is the Keeling Curve?
In 1958, chemist Charles David Keeling began measuring levels of atmospheric CO2 at the Mauna Loa Observatory in Hawaii.2 Carbon dioxide was measured in parts per million, which is “the number of molecules of CO2 for every million molecules of air.”3 Over the next several decades, measurement instruments like that at the Mauna Loa observatory were installed at over 100 locations around the world and confirmed that carbon dioxide levels were increasing. The graph that illustrates this steady increase is now known as the Keeling Curve.
4You may notice that the graphed Keeling Curve is jagged. An up and down variation of about 5 ppm occurs every year, corresponding with the cyclical seasonal changes in CO2 uptake. Carbon dioxide is taken in by land vegetation, most of which is located in the Northern Hemisphere. In the northern spring, levels of CO2 begin to decline as new plant growth removes CO2 through photosynthesis. When autumn comes, leaves drop and CO2 levels rise again. Over time the Keeling Curve has become one of the most famous scientific illustrations and has helped to launch the current debate over what to do about rising greenhouse gas levels.5
Carbon Dioxide and Temperature Increases
When Charles Keeling first started taking measurements at Mauna Loa in 1958, the atmospheric concentration of carbon dioxide was just 317 ppm.6 Using tree and ice cores, scientists can accurately reconstruct historical carbon dioxide information. Based on these records we know that CO2 levels in the late 1700’s were around 270 to 280 ppm. This means that human activity, especially post-Industrial Revolution, has led to a 43% increase in the amount of CO2 in the atmosphere.7 The current rate of increase is approximately 2 ppm per year.8
9Indeed, the Scripps Institution of Oceanography estimates the last time the concentration was at least 400 ppm occurred 3 to 5 million years ago, during the Pliocene Epoch. Although it is still very difficult to model the climate of the Pliocene,10 climatologists believe global average temperatures were 5.4-7.2 degrees Fahrenheit higher than today’s average temperatures and as much as 18°F warmer at the poles. Sea level ranged between 16 to 131 feet higher than today.11
sea levels will change over the next several decades. In the documentary An Inconvenient Truth, Al Gore illustrated the relationship between CO2 and temperature using a dramatic hydraulic lift.
The title at the upper left reads: “650,000 Years of CO2 and Temperature.” The scale at the left says, reading from bottom to top: “CO2 [ppm] 200; 250; 300; 350; 400.” The years before present along the bottom read “600,000; 500,000; 400,000; 300,000; 200,000; 100,000; 0.” CO2 concentrations are the red curve, and temperatures the light blue. The lower yellow dot indicates CO2 concentrations in 2006, and the upper yellow dot represents the projected concentration after another couple of decades. 13
As can be seen in the chart above, temperature and carbon dioxide levels have been correlated throughout geologic history.14 Temperatures between the years 2000 and 2010 are almost 1.8°F above the temperatures in the early 20th century. Moreover, we can probably expect more warming due to a temporary lag between more carbon dioxide and higher temperatures.15
Where Do We Go From Here?
Ralph Keeling, Charles Keeling’s son, now operates the Hawaiian Mauna Lao observatory. In a recent interview he said that crossing the 400 ppm threshold is largely symbolic. He elaborated:
It’s like turning 50… You don’t think that much about your age until you reach that milestone. You don’t think abut CO2 levels going up year by year—it s hardly newsworthy when levels go from 380 to 382—until you reach that landmark and realize the levels have gone up an awfully long ways.16
We’re already 50 ppm above the 350 ppm that many scientists have stated is the safe upper limit for CO2 levels in Earth’s atmosphere.17 Unless people pay attention to the 400 ppm benchmark and we begin to seriously slow the rate of greenhouse gas emissions, we’re on track to surpass 450 ppm within 30 years. As Ralph Keeling commented: “I wish it weren’t true but it looks like the world is going to blow through the 400 ppm level without losing a beat. At this pace we’ll hit 450 ppm within a few decades.”18
