Like your global warming entry. But I’ve long had a bone to pick about Keeling’s chart of CO2. The average lay reader would likely look at it and say the equivalent of, “wow, that’s a whole lot of increase, what a steep upward trend!” The somewhat more astute reader would look at the scale and think about its zero-based equivalent. The really astute reader wants to see the best available chart for that spot for the past, say, 10,000 or 100,000 years before offering any considered response. So much of interpretation and reaction depends on proper context! Some astute nay-says would point to this very chart and label it as a lie, or at best an incomplete and inconclusive set of data points.
Indeed. Now Dr. Keeling (and now others) reported his data in his eponymous curve, gathered at a time when others had not thought to collect such information. Of course, you are correct that if the vertical axis were to begin at zero, then it would be apparent that it shows about a 30% increase from 1956 to 2015, and not a 2000% increase. On the other hand, the interesting annual variations would not be visible, and in my opinion, those wiggles add to our conviction that the data shows something relevant about the atmosphere.
To figure out CO2 levels in the atmosphere at earlier times can’t rely upon direct measurements such as Keeling’s, because they weren’t done. Of course, some scientists investigated the composition of the atmosphere, and that’s how Lord Raleigh and Sir William Ramsay discovered argon and other inert gases 120 years ago. But those point measurements would not be suitable to estimates of global changes over long times. For such measurements today, scientists use other methods. For example, testing the composition of the gases trapped in ancient air bubbles within deep cores taken from Greenland glaciers.
Here’s some of that data, which meets your request to see long records, but, I’m afraid some of this still doesn’t go to zero. Here’s one, borrowed from the Wikipedia page Carbon Dioxide in the Earth’s Atmosphere. The inset chart’s horizontal axis spans 1000 AD to today, and the main chart shows the carbon dioxide concentration going back more than 400,000 years!
I grant that the vertical axis doesn’t go to zero, but you can clearly see that today’s CO2 levels are unprecedented over nearly half a million years, a span longer than the history of the human species. On this graph, you can also detect the end of the most recent ice age about 12,000 years ago. That’s the rapid increase in CO2 from below 200 ppm to about 260 or 280 ppm. For the span of recorded, settled human history the CO2 level and the Earth’s climate have been relatively stable, until about 200 years ago. The actual increase in CO2 isn’t the 30% from 305 to 400 ppm as shown on the Keeling curve, but about 50% from about 260 to 400 ppm. Thus for 10 or 12,000 years, the CO2 level fluctuated around 260 ppm, then in 200 years it moved steadily upward about 50% and appears to be rising steeply.
Senator Marco Rubio, elected by the locals before I moved to Tampa, says that the climate is always changing, which is true, and that it has not been decided among scientists that humans are the cause. He is correct about climate, as you can see from the fluctuation between ice ages and warmer interglacial periods during the past half million years. In so far as these fluctuations arise from CO2, the sources of the CO2 are natural; that is not due to human activity. Humans didn’t exist throughout the first half of the period shown, and they were hunter gatherers only burning firewood and not numerous in any case, until the end of the last ice age. Does the change in CO2 during the past 10,000 years look to you as if it were just one of the earlier, natural, and typical fluctuations? When Sen. Rubio says that the climate has always changed, he is suggesting that the world’s climate scientists don’t know this fact, which Sen. Rubio knows, and that the climate scientists are warning us about a typical change in the climate.
Well, to be precise, this data is not a measure of the climate. It is a measure of one of the factors that influence the climate. Just thinking of the greenhouse gases, the researchers tell us that water vapor is the most important, carbon dioxide next, and then methane and other gases. Importance arises from the quantity of a gas and from its absorption of electromagnetic radiation in the long wavelength infrared. Carbon dioxide tends to fill in some of the gaps in water’s absorption spectrum. The data shows that during the past half a million years, the CO2 concentration has fluctuated, along with major climate swings, from less than 200 ppm to more than 250 ppm, plus and minus about 10% or 15%, and I’d say that the time scales for these natural fluctuations are thousands to tens of thousands of years. This is in contrast to the past 200 years, which have seen the 50% swing, still continuing, in a hundred years.
Sen. Rubio pretends that there is scientific disagreement about the extent of human involvement. But the world’s climate scientists have gotten together under the auspices of the United Nations to tell us what they believe, indeed what they know, on this subject. As for this particular point, the carbon dioxide concentration, there isn’t significant disagreement. There is not much disagreement on the other major points, say, of the temperature change, which I’ll discuss in future posts.
Here’s another data graph for you, also from the Wikipedia page, and this one has its vertical axis go to zero.
This one extends over more than 500 million years! Recent times are on the left, and moving to the right goes into the distant past. This span of time is a thousand times longer than the earlier one I showed. The measurement methods are different too. The first graph’s data comes from air bubbles preserved in ice removed from the deep glaciers in Greenland, and similar data in Antarctica. This data arises from measurements of carbon isotope ratios preserved in ancient rocks. The Royer Compilation, the dots, shows data, and there is also an averaged value for this. Notice the large error bars. The other three curves come from models in which the researchers try to estimate carbon dioxide sources and sinks. There on the left is your axis starting at zero. Taking today’s geological age as typical, the right hand axis shows the ratio of the past CO2 levels to those of today.
Whoa! In the past the CO2 levels have been five, ten, twenty times higher than today. Of course, the climate was different than today’s too. There have been major ice ages, and also major warm phases, when the climate was much warmer than today’s. For example, the climate during that period when the plants for formed today’s coal deposits lived among dragon flies with 2 meter wing spans.
Thus the problem with today’s recent increases in CO2 isn’t that the levels are unprecedented or even the highest ever. The problem is that the levels are changing with unprecedented speed, the biosphere will be unable to adjust as rapidly, and that the changes are taking us rapidly away from levels that have existed throughout the entire span of settled human culture and civilization. Of course, there are now many more humans, and hundreds of millions of them live where they will be flooded out, and billions of them, really all of us, depend upon agriculture that has arisen during the generally favorable and temperature conditions of the past 10,000 years.