This is the 6th episode in a series recounting the history of measurements and data related to Global Climate Change. If you’re just joining, you can catch up on the previous episodes:
- Episode 1: Beginnings (or two British scientists’ adventures with leaves and CO2 measurements)
- Episode 2: First measurement of anthropogenic global warming
- Episode 3: Our “large scale geophysical experiment” (1940-1960)
- Episode 4: Dave Keeling persists in a great idea
- Episode 5: Icy time capsules
“I absolutely do not believe in the science of man-caused climate change. It’s not proven by any stretch of the imagination. It’s far more likely that it’s sunspot activity or just something in the geologic eons of time.”
-My own U.S. Senator, Ron Johnson, R-WI (Journal Sentinel, August 16, 2010)
“It’s a very complex subject. I’m not sure anybody is ever going to really know.”
-Donald Trump (New York Times interview, November 22, 2016)
“I think that measuring with precision human activity on the climate is something very challenging to do…”
-Scott Pruitt, EPA Administrator (CNBC Interview, March 9, 2017)
Mr. Pruitt is right, of course. Measuring with precision [the influence of] human activity on the climate is indeed challenging. Just like landing folks on the moon and returning them safely home. Or sending automobile-sized robots to drive themselves around on Mars taking photographs and analyzing soil samples and sending the results back to us on Earth. Or making giant aluminum tubes with wings that can carry hundreds of people by air to destinations anywhere on the globe in 24 hours or less with a safety record better than that of horse-drawn carriages. Or eradicating smallpox. Or making it possible for most of us to communicate with one another using our voices, text, images or videos, globally, in real time and at a moment’s notice, with little wireless devices we carry around in our pockets.
Once you recall we have accomplished all those rather challenging things, you may not be shocked to learn we have, indeed, also measured with precision the influence of human activity on the climate. Not only that, as we have seen in previous episodes and will continue to see, scientists have made these high-precision measurements publicly available. Anyone with web access can download and review much of the data. The detailed methods with which the precision measurements were conducted, and the resulting data analyzed, are also publicly available in scientific publications, the quality of which have been verified through peer-review (many of these are accessible as links on this website). Presumably, as Head of the United States Environmental Protection Agency, Mr. Pruitt has ready access to means for reviewing the precision measurements at his convenience.
And, as it turns out, we don’t have to speculate, as Senator Johnson evidently does, about mysterious somethings (sunspots maybe?) in the “geologic eons of time.” That’s because, as we saw in Episode 5 of this series, evidence of events during those “geologic eons” is available for study.
In Episode 5, we saw how tiny bubbles of old atmospheres, trapped and preserved in ice as deep as three quarters of a mile below ground at Law Dome, Antarctica, and extracted from ice cores, have enabled us to construct a measured record of atmospheric CO2 concentration over the past 2000 years. Thanks to the exceptionally high rate of snowfall at Law Dome, this 2000-year record has a very high resolution. But ice cores have been extracted at other locations in Antarctica, too, and some of those locations feature deeper ice.
The deepest ice cores have been extracted by the European Project for Ice Coring in Antarctica (EPICA) at Dome C. EPICA has extracted ice cores three miles deep at Dome C, and those ice cores contain air bubbles trapped up to 800,000 years ago. Additionally, a collaborative project between Russia, the U.S., and France extracted ice cores as deep as 2.25 miles below ground at Vostok station, from which have been captured atmospheric samples from up to 420,000 years ago. Combining CO2 measurements from the Dome C ice cores, Vostok ice cores, Law Dome ice cores, and direct atmospheric measurements at Mauna Loa and the South Pole gives us this continuous plot of atmospheric CO2 concentrations going back a whopping 800,000 years:
More details about the measurement methods and access to the data sets are available at this website and by clicking links to the original scientific publications in the caption above.
The green and blue colored data in the graph above are the 2000-year Law Dome measurements and direct atmospheric CO2 measurements since 1958, respectively, that we plotted in Episode 5. They are shoved way over to the right now, dwarfed in time by the massive amount of historical data collected from the deeper ice cores at Vostok and Dome C.
I’m not sure what Senator Johnson meant by “the geologic eons of time.” But, insofar as we are interested in how CO2 has changed over a time period of interest to the success and survival of humans on Earth, I’d say 800,000 years fits the bill. To put that in context, anatomically modern humans appeared on the planet only 200,000 years ago. So, the CO2 record above goes back 4 times as long as the entirety of human experience. In fact, it goes back 200,000 years longer than fossil evidence of Homo heidelbergensis, the hominid thought likely to be the common evolutionary ancestor of Neanderthals and humans. (I included these and some other human and hominid milestones on the graph above. I find this useful for the purpose of putting geological and human events in perspective.)
In Episode 5, we saw that, over the past 2000 years, humans experienced atmospheric CO2 concentrations between 272 and 284 ppm prior to the Industrial Revolutions when we started to burn gobs of fossil fuels. The data in this episode extends that range somewhat, to a human experience of 184-287 ppm. The maximum pre-industrial concentration in human experience occurred 126,000 years ago, and it was roughly matched at the time of the Second Industrial Revolution, when we started to burn oil at an industrial scale. Since then, it has been up and up, such that our CO2 level as of April 29, 2017 is 43% higher than the maximum CO2 level over the entire pre-industrial experience of humans spanning 200,000 years.
And, in the context of the “geologic eons of time,” this is happening quickly! As we did for the shorter data set in Episode 5, we can take the derivative of the graph above to see the rate of change of the atmospheric CO2 concentration in parts per million per year:
The answer is the same as we saw in Episode 5, but it’s all the more striking in the context of an 800,000 year record. Not only are we far above any “natural” CO2 level in the past 800,000 years, since the Industrial Revolutions we have been increasing that CO2 level at a rate much faster than Earth has experienced over at least that time period. And the rate of increase continues to accelerate.
When you hear about “controversy” in climate science, uncertainties about the Earth’s response to this super fast rate of change is what it’s about. It’s not about whether CO2 from our burning of fossil fuels is causing global climate change. (It is.) The uncertainty (which the popular media may refer to as “controversy”) is about how extremely and how quickly Earth’s climate will respond to the rapid change in atmospheric CO2. Questions like: How quickly will the land-based ice sheets in Antarctica and Greenland melt, contributing to sea level rise? How much and how quickly will the reduced reflectivity of the Earth, as a result of the melting of the reflective snow and ice, contribute to additional warming?
To a scientist, like myself, who is experienced in rate-of-change graphs, the plot above is terrifying. It’s what we refer to as, “going vertical.” That is, departing from the normal process at an accelerating rate. I, myself, am a product developer experienced with defining and controlling the conditions required to manufacture new products. People like me want to keep a graph of a critical process parameter (in this case, CO2 concentration) within narrow limits. From this point of view, the Earth has “manufactured” humans. This has occurred, until very recently, within narrow limits of the atmospheric CO2 concentration. We are now departing rapidly from those narrow limits. As an engineer, I would say we need to get that critical process parameter back in control, as soon as possible. Otherwise, we risk a failure of our manufacturing process. Since the manufactured product, in this case, is us, we have a strong interest in getting the process under control.
Stay tuned for Episode 7, where we link the historical CO2 record directly to the global temperature record.
To be continued…