Past Climate Variability and Change in the Arctic and at High Latitudes

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The U.S. Climate Science Program Chapter 3
The warming from the
Little Ice Age began for
largely natural reasons,
but it appears to have
been accelerated by
human contributions and
especially by increasing
CO 2 concentrations in
the atmosphere.
extended to equatorial regions and caused a seesaw
response in the far south (i.e., mean annual
warming in the south when the north cooled).
Large changes in extent of sea ice in the north
AtlAntic were probably responsible, linked to
changes in regional to global patterns of ocean
circulation; freshening of the north AtlAntic
favored expansion of sea-ice.
These abrupt temperature changes also were a
feature of the current interglacial, the Holocene,
but they ended as the lAurentide ice Sheet on
cAnAdA melted away. Arctic temperatures in the
Holocene broadly responded to orbital changes,
and temperatures warmed during the middle Holocene
when there was more summer sunshine.
Warming generally led to northward migration
of vegetation and to shrinkage of ice on land
and sea. Smaller oscillations in climate during
the Holocene, including the so-called Medieval
Warm Period and the Little Ice Age, were linked
to variations in the sun-blocking effect of particles
from explosive volcanoes and perhaps to
small variations in solar output, or in ocean circulation,
or other factors. The warming from the
Little Ice Age began for largely natural reasons,
but it appears to have been accelerated by human
contributions and especially by increasing CO 2
concentrations in the atmosphere (Jansen, 2007).
3.6.2 Arctic Amplification
Based on paleoclimate data, Arctic amplification
is a pervasive feature of Earth’s climate
system over a range of forcing scenarios. It must
be remembered that no particular past interval
offers a perfect analogue for conditions in the
coming decades as greenhouse gases increase,
and that the paleoclimatic record often does not
allow reconstruction of the spatially distributed
rate of change in response to rapid forcings.
Nonetheless, larger changes in the Arctic than
hemispherically or globally are expected based
on physical understanding and models, and
this expectation is confirmed by the available
paleoclimatic data.