| Climate changes over the last 1000 years have been smaller than those over tectonic, orbital, and glacial-age millennial time scales, never exceeding 1°C on a global basis. | |
| Climate changes over the last several thousand years have been highly variable in pattern from region to region. | |
| Over much of this interval, records of climate are based on geochemical and geological indicators stored in annually layered archives: mountain glaciers, tree rings, and corals. | |
| Also available are historical observations recorded by humans. |
Major Climate Variations Events
| Longer Time Scales | |
| Cooling during the Little Ice Age (A.D. 1400-1900) | |
| Warming in the twentieth century | |
| Decadal Time Scales Climate Variability | |
| Pacific Decadal Oscillation (PDO) | |
| Interannual Time Scale Climate Variability | |
| El Nino Southern Oscillation (ENSO) | |
| North Atlantic Oscillation (NAO) |
| Medieval Climate Optimum: A relatively warm climate near 1000 to 1300. | |
| Little Ice Age: The cooling during 1400-1900 that seriously affect Europe. | |
| Twentieth-Century Warming |
What Caused the Little Ice Age?
| The Little Ice age cooling was simply the culmination of a slow orbital-scale cooling. | |
| If this is true, the medieval optimum warm interval may have been just an insignificant blip during an ongoing cooling trend. | |
| The Little Ice Age was the most recent in a series of distinct millennial oscillations. | |
| If this is true, the medieval optimum and preceding centuries may represent the warm extreme of a millennial oscillation, with a shift toward the cool extreme during the Little Ice Age. | |
What Caused the Twentieth-Century Warming?
| The warming is a result of human impacts | |
| This explanation will be true if the warming of the twentieth century has been unprecedented in magnitude over the last 1000 year or more of recent climate history. | |
| The warming is part of the natural variability | |
| This explanation will be true if comparable warm intervals occurred before or even during the Little Ice Age. |
| “Pacific Decadal Oscillation" (PDO) is a decadal-scale climate variability that describe an oscillation in northern Pacific sea surface temperatures (SSTs). | |
| PDO is found to affect Alaska salmon production cycles. | |
| PDO is found to link to the decadal variations of ENSO intensity. | |
El Nino-Southern Oscillation (ENSO)
| ENSO is a interannual (year-to-year) climate variability in the eastern tropical Pacific Ocean. | |
| ENSO is found to have profound impacts on global climate. |
Walker Circulation and Ocean Temperature
Walker Circulation and Ocean Temperature
Walker Circulation and Ocean Temperature
Walker Circulation and Ocean Temperature