There is, however, still a degree of uncertainty about which came first—a spike in temperature or CO2.
was stable over the last millennium until the early 19th century. isotopic data) confirm that the increase must be due to emissions of CO from fossil fuel usage and deforestation.
It then started to rise, and its concentration is now nearly 40% higher than it was before the industrial revolution (see Fig. Measurements from older ice cores (discussed below) confirm that both the magnitude and rate of the recent increase are almost certainly unprecedented over the last 800,000 years.
The wide margin of error in the EPICA core data is due to the way air gets trapped in layers of ice.
Snowpack becomes progressively denser from the surface down to around 100 meters, where it forms solid ice.
Ice core measurements allow us to extend this way back into the past.