|
|
|
|
|
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. |
|
|
|
|
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 |
|
|
|
|
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. |
|
|
|
|
|
|
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. |
|
|
|
|
|
|
|
|
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. |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Notes