By analyzing shells buried under the Atlantic seabed, off the coast of Africa, researchers from the Lamont-Doherty Earth Observatory have determined that current atmospheric concentrations of greenhouse gasses are significantly higher than they have been for more than 2.1 million years. Whereas current levels are at 385 parts per million (ppm), the average over the span was a mere 280ppm, the same approximate level as existed in Earth’s atmosphere before the Industrial Revolution. One thing this work helps to confirm is that the current level of greenhouse gasses in the atmosphere is not part of any natural cycle that has taken place during the span in which human beings have existed. Our emissions are projecting the climate in a direction that is unprecedented in the history of human life.
The technique employed was based on examining boron isotopes in foraminifer shells. The work was published in Science.