text: Over time, thermometers are added, and they slowly migrate south and to both the new, and old, worlds . Eventually, about 1900 A.D., there are sufficient thermometers on the globe to get a partial idea what is happening . But climate is subject to cyclical changes. Some, like the Pacific Decadal Oscillation, have about a 40 to 60 year full cycle length. Others, like solar cycles that run 178 years, and Bond Events a 1500 year cycle , are a bit longer. A 100 year record is inadequate to allow for these events.