Role of the Arctic in Climate Variability

With respect to the first question, a number of explanations have been invoked, including in the case of colder periods (glacials) the generally higher albedo due to increased snow and ice covers (Hansen et al., 1984; see Albedo), a larger concentration of aerosols as a result of increased aridity or higher wind speeds (Harvey, 1988), and lower concentrations of atmospheric greenhouse gases (Barnola et al., 1987; Raynaud et al., 1993). All of these factors contribute to a less positive radiation balance, that is, a decrease in net warming in the Earth's surface.

While important in a general sense, these factors do not suffice to explain the coupling between climate variability of the Northern and the Southern Hemisphere with respect to the 23,000- and 41,000-year forcing. Atmospheric general circulation models results (Manabe and Broccoli, 1985) demonstrate that simulated albedo effects of ice sheet changes on one hemisphere such as those mentioned above do not effectively propagate across the equator to the other hemisphere through the troposphere (Alley, 1995). However, various paleoclimate proxy data show that global temperatures are linked to insolation at high northern latitudes. Thus, global warming is detected when insolation is large during summers in northern regions irrespective of insolation values in Southern Hemisphere summers (Imbrie et al., 1992). In particu lar, a general warming trend is paralleled when summers are warm and winters are cold in the Arctic, while a global cooling trend is observed when northern winters and summers are cool (Imbrie et al., 1992, 1993).

In summary, the comparison between paleoclimatic records and calculated orbital forcings of climate variability indicates that global climate variabilities at 23,000- and 41,000-year periods are strongly linked to variations in insolation at high northern latitudes (Alley, 1995).

Various explanations have been invoked with respect to the 100,000-year climate cycle, which is not linked to insolation variations. It is important to note that the variation in eccentricity serves mainly to modulate the precessional cycle. The timing of the perihelion (the point in its orbit where the Earth is closest to the sun) has a significant effect on seasonal insolation at times when the eccentricity of the Earth's orbit is high, while a nearly circular orbit leads to lesser forcing by changes in the precession of the Earth's rotation axis. Thus, it is expected that the amplitude of the precession cycle varies with a 100,000-year periodicity (Alley, 1995).

Attempts to model the response of the climate system to the 100,000-year eccentricity cycle of the Earth's orbit prove successful when a moderately slowly responding element is considered as part of the global climate system. Examination of paleoclimate records reveals a strongly asymmetric behavior of the 100,000-year climate cycle, with a slow onset of Ice Age conditions and a rapid transition from Ice Age conditions to interglacials. This characteristic is matched by numerical models if the aforementioned slow element of the climate systems leads to the observed rapid transition after a certain glaciation threshold is exceeded (Alley, 1995). While there may be several candidates qualifying as the slow climate element, the only plausible one seems to be represented by continental ice sheets at midlatitudes, for example, the Laurentide ice sheet in North America or the Fennoscandian ice sheet in northeastern Europe. Ice sheets are characterized by a highly asymmetric response to climate forcing. While the buildup of an ice sheet is fed by the relatively slow rate of snow accumulation, the collapse of an ice sheet takes place at the much faster rate of surface melting and/or dynamic collapse following the crossing of a glaciation threshold that gives rise to several positive feedbacks and accelerates ice sheet shrinkage.

Thus, ice sheets in general and—due to their size— the large, Arctic-derived Laurentide and Fennoscandian ice sheets in particular appear to be well suited to translate the 23,000- and 41,000-year cycles into the 100,000-year climate cycle (Alley, 1995).

While these conclusions still await further substantiation, it seems clear that orbital forcings of high northern latitude insolation in concert with the relatively slow response of large ice sheets such as the Laurentide or Fennoscandian ice sheets provide plausible explanations for climate variability on the millennial time scale. This underlines the role of the cryosphere in general and the Arctic in particular for natural climate variability and the glacial-interglacial cycles that have dominated the last million years of Earth's history.

Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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