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resemble those of the tree-ring reconstructions of Arctic mean annual temperatures
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these records reflect some data overlap, but also the strong linkage between the AO
and Arctic temperatures. Similarly, instrumental observations support a strong rela-
tionship between AAO and temperature in southern South America during the past
50 years, suggesting that long-term trends in temperature across Patagonia during
the past centuries have also been influenced by changes in the AAO (Thompson and
As the reconstructions from high latitudes in both hemispheres indicate large
similarities in temperature changes for at least the past 300 years, we could infer
some common forcings of annular modes of climate variability in both hemispheres
during the past centuries. Presumably, any climate change mechanism that projects
onto the meridional temperature gradient between the middle and high latitudes
may affect the polarity of the annular modes. Recent trends in tropical sea surface
been hypothesized (but not yet demonstrated) that a similar link may exist for the
Interactions between low- and high-latitude circulation modes are difficult to
document based on the current array of climate-sensitive chronologies and forcing
reconstructions. For example, interannual and decadal modes of tropical climatic
variability such as ENSO and PDO strongly affect weather conditions in low lati-
tudes of the western Americas, but their influences on the climate of the extratropics
have been noted here and widely documented elsewhere. On the other hand, the
annular modes have large amplitudes at extratropical latitudes, but several studies
reveal that they have a substantial signature at lower latitudes as well (Thompson
Reflection symmetries about the equator in interdecadal ocean temperature dur-
ing the past four centuries suggest that the tropical Pacific has played a pivotal
role in linking westerly winds in both hemispheres through meridional telecon-
temperature-sensitive records from the Gulf of Alaska and northern Patagonian
are coherent on long-term (>10 years) oscillatory modes, largely in response to
ENSO-like decadal to interdecadal modes of variability in the Pacific Ocean.
However, instrumental records show that high-latitude forcings of climate variabil-
ity also affect both regions. For example, recent trends in Alaskan climate are better
explained by the juxtaposition of ENSO-like and AO-related SLP variability over
the north Pacific.
The 'ENSO-like' interdecadal variability, as documented in Trenberth and
north Pacific in conjunction with warming over western Canada and Alaska. Apart
from that feature, SLP over the north Pacific has risen slightly during the past 30
year, consistent with the trend toward the 'high-index' state of the AO during this
period. That the trend in the SAM accounts for approximately 50% of the warm-
ing over the Antarctic Peninsula and southern Patagonia attests to the importance
of climate mechanisms other than ENSO over this region. In consequence, the
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