John Tyndall builds the world's first ratio spectrophotometer and tests the absorptive properties of atmospheric gases.

Svante Arrhenius completes his calculations on varying CO2 levels.

Atmospheric CO2 levels are 290 parts per million.

CFCs are invented.

The National Academy of Sciences issues its first major report on Global Warming: "We may not be given a warning until the CO2 loading is such than an appreciable climate change is inevitable."

Atmospheric CO2 levels are 337 parts per million

The IPPC issues its Third Assessment Report: "Most of the warming observed over the last fifty years is attributable to human activities."

A report by the National Research Council requested by President Bush states: "Greenhouse gases are accumulating in Earth's atmosphere as a result of human activities, causing subsurface ocean temperatures to rise. Temperatures are, in fact, rising."

President Bush announces that the United States is withdrawing from the Kyoto Protocol.

Senator James Inhofe, R-Okla., chairman of the Committee on Environment and Public Works, says he has "compelling evidence that catastrophic global warming is a hoax."

The American geophysical Union issues a consensus statement asserting: "Natural influences cannot explain the rapid increase in global near-surface temperatures."

Extent of melt on the Greenland ice sheet reaches a record maximum.

Arctic sea ice reaches a record minimum; researchers warn sea could be ice-free in summer "well before the end of the century."

Kyoto Protocol goes into effect.

The National Academy of Sciences of the eight major industrialized nations issue a joint statement: "The scientific understanding of climate change is now sufficiently clear to justify nations taking prompt action."

Sen. James Inhofe, R-Okla., surrenders the gavel to Sen. Barbara Boxer, D-Calif. Hope springs eternal.