It's pretty simple. In the middle of the 19th century, Tyndall demonstrated that certain gases absorb heat, among them CO2, CH4, and H2O. In 1898 or so, Nobel physicist Svanti Arrhenius proposed the greenhouse effect, and calculated that a doubling of CO2 would increase the temperature of the planet from 2-6 degrees C, IIRC.
After that, it's just a matter of collecting data, like atmospheric CO2 levels and temperatures, and confirming those with studies on the response of plant and animal species, such as changes in bloom dates, migratory seasons, etc. |
