Is the transport of heat northward by the Gulf Stream and North
Atlantic Drift, and its subsequent release into the mid-latitude
westerlies, the reason why Europe's winters are so much milder than
those of eastern North America and other places at the same latitude?
Here, it is shown that the principal cause of this temperature
difference is advection by the mean winds: southwesterlies bring warm
maritime air into Europe and Northwesterlies bring frigid continental
air into northeastern North America. Further analysis of the ocean
surface heat budget shows that the majority of the heat released
during winter from the ocean to the atmosphere is accounted for by the
seasonal release of heat previously absorbed and not by ocean heat
flux convergence. Therefore, observationals indicate the winter
temperature contrast between Europe and eastern North America is
explained by the maritime-continental climate distinction, and not by
ocean circulation.Experiments with numerical models confirm this conclusion
and
illuminate the importance of the Rocky Mountians for the climatological
difference in winter temperatures across the North Atlantic, and the
difference in the temperatures of western Europe and western North
America.
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The instrumental record of the state of the climate system extends
100-200 years; it tells a tale that allows us to build an expectation
of what is typical, and what should be considered to be an extreme
event (e.g., the Dust Bowl). When the historical record is extended
using proxy indicators for the state of the climate system, one finds
"Climate Surprises": the global climate system can undergo much
larger, rapid climate changes than anything imaginable based on the
instrumental or phenological record. These events include mega-droughts
(continental scale, long-lived droughts) and the so-called
Dansgaard-Oeschger events.
What is in store for the future? Projections indicate the burning of
fossil fuel will cause the concentration of carbon dioxide in the
atmosphere to increase by two- or three-fold within the next few
hundred years. This "experiment" is extraordinary because carbon
dioxide will increase at a rate that is perhaps 100 times faster than
the natural cycle, and because it has been since the Eocene (50
million years ago) the Earth has experienced such high levels of
carbon dioxide. The Intergovernmental Panel on Climate Change (IPCC)
has used state-of-the-art climate models and has concluded the
increases in carbon dioxide will cause a rather smooth transition to a
much different climate from what we have experienced in the past.
Based on the abrupt changes seen in the paleorecord, some scientists
have speculated that this transition may be much more volatile than is
projected by the models. Furthermore, lessons from studying the
paleorecord suggest the models may be seriously underestimating the
amplitude of the projected warming of the wintertime polar regions.
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