CO2 vs Temperature: Last 400,000 years

CO2 vs Temperature: Last 400,000 years
"Over the last 400,000 years the natural upper limit of atmospheric CO2 concentrations was about 300 ppm. Today, CO2 concentrations worldwide average about 370 ppm. Humans may be able to take credit for some of these additions, but not all of them. Earth's plant life will respond to soak up these additions with additional biologic activity, but this takes time. Meanwhile perhaps up to 9% of CO2 concentrations in the atmosphere today may be attributable to human-related activities like agriculture, industry, and transportation. Compared to former geologic periods, concentrations of CO2 in our atmosphere are still very small and may not have a statistically measurable effect on global temperatures. For example, during the Ordovician Period 460 million years ago CO2 concentrations were 4400 ppm while temperatures then were about the same as they are today."