Humans are altering atmospheric composition

• carbon dioxide concentration has increased by ~31% since 1750

• the carbon budget: nature has absorbed roughly half our emissions

• there is no question that the increase is unnatural

• from a very long term perspective, these changes are enormous

Previous slide

Next slide

Back to first slide

View graphic version

The 20th century warming coincided with an abrupt increase in many greenhouse gases. (Note that about half of the increase in CO2 has taken place in just the last 40 years.) The increase in CO2 in the last 250 years is more than the typical increase from an ice age to an “interglacial” period. Current values of CO2 are higher than at any time in the last half million years and are probably higher than at any time in the last 20 million years.