Continuing on how a small change in a trace gas can have big impacts I want to consider what an approximate 0.03% increase in the overall concentration of CO2 in the atmosphere might do.
The lowest approximate concentration of CO2 estimated for the atmosphere in the last few hundred thousand years is about 190 parts per billion (ppm). 0.000190 CO2 molecules per ever one molecule in the atmosphere. Doubling that would be 0.000380 CO2 molecules, which is were we are now. Since the last major ice age, CO2 has doubled.
Arrhenius in his 1896 paper was attempting to prove that CO2 triggered the ice ages to warm period transitions. As I have noted before, his final table showed the temperature response over land and water for a change in CO2 from 0.67 to 1.5 from the value of his day, over 100 years ago. Based on his calculations, we are near the peak value of the Holocene. Arguably, we are near the peak value of the Holocene, about the last 12,000 years.
One thing Arrhenius did not address in his paper was how the Earth entered the ice ages. His thoughts were that CO2 was the driver, but what reduced the concentration of CO2 if it was the climate driver?
Callendar, in the 1930s also pondered the role of CO2 in climate. He determined that the impact of CO2 approached two degrees as the concentration of CO2 approach a doubling and that the impact leveled off at that point. From his day to now, CO2 is approaching a doubling and temperature response is arguably approaching 2 degrees.
After Arrhenius' paper, Angstrom commented that CO2 was approaching saturation meaning that CO2 could not produce the range of temperatures that Arrhenius had predicted. Based on Arrhenius' final table and his unpublished retraction of the range of temperatures he predicted in his 1896 paper, 1.6 (2.1) with water vapor was his estimated range was in agreement with Callendar which is in agreement with the saturation Angstrom mentioned, which is in agreement with the current temperature data, all seem to indicate that 2 degrees is roughly the maximum impact of CO2.
Ramathan, discussed in this post on the Science of Doom, also seems to agree if you carefully consider his work. In the block diagram of the CO2 warming process, he list the direct impact of CO2 on the surface for a doubling to be 1.2 degrees. Any further warming would involve interaction with water vapor. Since his initial concentration of CO2 was greater than 190ppm, approximately 280 ppm, his results are in general agreement with Arrhenius, Callendar and Angstrom.
For some reason though, current science still disagrees that CO2 has an impact on climate but that impact is limited. So how does a guy or gal at home figure out for themselves who to believe?
Why not do an experiment at home? So for a simple experiment find an aquarium that is not currently occupied by living fish. Fill the aquarium with clean water. tape a piece of newspaper on one side and the back of the aquarium and read the print. The print should be about the same size on the side and back.
Drop one drop of black ink in the water. Read the print after the ink diffuses in the water again trough the aquarium from the side and from the front.
Now put one more drop of ink in the aquarium and read again.
How much harder was the paper to read after one drop? How much harder was it to read after two drops?
If you want to make the experiment really scientific, measure 999,998 drops of clear water into the aquarium. Once you add the two drops of ink, you have 2 parts per 1,000,000. Now add 188 more drops and you have 190 parts per million roughly.
If you have a photographer in the house, you can use a light meter to measure the amount of light passing through the aquarium. As long as you have a relatively good light source and light meter, you can measure the change per drop or tens of drops and record the results for graphing both from the ends and from the front of the aquarium.
To make the experiment even more scientific, you can use red ink with a red light and green ink with a green light. Then compare one or both of those to the reading of a white light. The red and green light measured reduction in intensity will reduce more than the white light intensity. You have just modeled the atmospheric response to a change in opacity.
To really kick the experiment up to quality scientific standards, repeat the experiment with red and green inks. Add both the red and green at the same times and at the same amounts until you have a data to about 400 drops for each ink.
Have fun! After you have all the data you want, plot the data and fit a curve to the changes. What does the curve look like from one end to the other? What does the curve look like from front to back? So you can read from front to back a little better than from end to end?
The end to end represents the surface looking up to space. The front to back represents some point in the sky looking up to space. Think about it.
I will work on an experiment for change in conductivity with more CO2. It will not be as much fun because the plot is boringly straight.
Oh, should you see someone dramatically demonstrate that one drop of ink in pure water makes a big difference, think about how much difference that one drop makes if it happens to be drop number 401.
This brings me to the fun part of the impact of the change in concentrations. Optically, the increase is reaching a plateau. Constructively, it is just a slow boring increase. Each impact has effects on different feed backs with different time constants. Radiant forcing is quick. In just a decade or two there can some indication. Conductivity takes a long time to have an impact. Thousands of years maybe tens of thousands of years. Nothing like that in the climate records though :)