CO2 and Temperature Fluctuations

Unanswered Question

We have seen that there have been fluctuations in both temperature and CO₂ emissions in the past 400,000 years. This leads to an important question:

• Did the atmospheric CO₂ concentrations and temperatures change prior to the pre-industrial period or only after it?

Or more specifically:

• If we attribute the mean global temperature increase of 1ºF over the past century to human activities, how do we explain the mean global temperature fluctuations between +4ºF to -17ºF that occurred thousands of years ago, when there was no human activity?

Possible Answer

Some argue that temperature change is natural and cyclical. Thus, since it is cyclical, we, the humans, might not be influencing the current change in the climate.

The most important difference between now and then that we have to keep in mind is the human species. More than six billion people live on this planet now, who were not there during those earlier natural temperature cycles, and any chances that jeopardize the existence of this humankind must be taken seriously. The reasons for concern are discussed next.

More than 6 billion people live on this planet now who were not here during the earlier natural temperature cycles, and any chances that jeopardize the existence (land and food supply) of this humankind must be taken seriously.

The significant temperature fluctuations shown in the earlier graph of the ice core samples led to the glacial and inter-glacial ice ages. The temperature increase over the last 150 years, however, is not significant compared to the changes in the past known history. Let’s take a closer examination of the CO₂ profile.

Instructions: Click on the buttons below to graph and compare CO₂ and temperature on one graph, and then respond to the question that follows:

From the graph above, we know that CO₂ concentration did not rise above 310 ppmv at any time from 400,000 years ago to the year 1950, even though the temperatures continued to increase. Based on this information, we can conclude that this increase is something that the atmosphere did not experience earlier, which means that the increase is the result of human activity.

Now let’s look at how CO₂ concentration and temperature have changed in the last 50 years, since 1960.

CO₂ concentration versus temperature change graph.

Text description of the CO₂ concentration versus temperature change graph.

Based on your observations of the above graph, reflect on the questions discussed below:

1. In the past, 310 ppm of CO₂ increased the temperature by about 4 degrees F, so how do you think the current CO₂ concentration of 370 ppm is impacting the temperature?
2. How long will it take for the temperature to come to a level that corresponds to the CO₂ concentration of 370 ppm? Or are we already there?
3. What will the consequences be if the concentration of CO₂ increases to 550 ppm (double the pre-industrial concentration), or even to 70 ppm (both of which are proposed to be likely scenarios with the increased fossil fuel consumption?)

If the temperature already reached the maximum temperature corresponding to 370 ppm, then some other factors are cooling the planet that were absent in the previous cycles.

Now, let’s examine the reasons or causes for the natural fluctuations.