But anyone who looks at the data (shown in Figure 1) will see that no matter which caused the other, the changes in temperature from ice-age cold to interglacial warmth are about 10C while the change in CO 2 is about 100ppm. Since the late 1800s, the temperature has warmed a bit less than 1C , while the CO 2 concentration has increased by a bit less than 100ppm. In other words, the natural, historical relationship between CO 2 and temperature is about 10 times weaker than that observed over the past 100 or so years. Thus, there is no way that the temperature rise from the Little Ice Age to the present can be the cause of an atmospheric CO 2 increase of nearly 100ppmthe reasonable expectation would be about 10ppm. This line of reasoning is off by an order of magnitude.