At 4.52 billion years of age, our planet is no spring chicken.
While still young compared with the age of the universe (about 13.7 billion years), it has seen and experienced a lot of weather and climate. One big climate-changing event about 65.5 million years ago occurred when a space rock, about 6 miles in diameter, and traveling an estimated 15 miles per second, slammed into Earth's surface in the Yucatan in northeast Mexico.
Its mass and kinetic energy was so great that it plowed miles deep into the Earth's mantle creating a crater that is about 120 miles wide. Then things got really interesting. The underlying carbonate and sulfate rocks released hundreds of billions of tons of water vapor, carbon dioxide and sulfur dioxide gases. An enormous plume of these gases along with ash, dust, rock, boulders and all manner of debris erupted into the sky and was globally distributed with huge consequences. At least it was for the dinosaurs. It is believed they all died in a short period of time.
This event is an excellent definition of "climate forcing." This climate-forcing event caused fires to burn for a long time, and along with the ash, hid the sun. More than 50 percent of the land and ocean species disappear from the fossil record. A recent paper in Science (Vol. 327, 5 March 2010, p1214) with 33 authors reaffirm these events. Many other sudden and not-so-sudden forcing events have occurred during Earth's long history.
A not-so-sudden climate-forcing event discussed in this column previously is the formation, and subsequent melting, of huge glaciers during the many ice ages that have occurred in the past. The Earth's orbital cycles detailed in the Milankovich theory are believed to be responsible for these events. They take place over thousands and tens of thousands of years. In a way, these two natural episodes mark the natural bookends of climate change from the very sudden to the lengthy.