hemispherically, the "Little Ice Age" can only be considered as a modest cooling of the Northern Hemisphere during this period of less than 1☌ relative to late twentieth century levels. Thus current evidence does not support globally synchronous periods of anomalous cold or warmth over this interval, and the conventional terms of "Little Ice Age" and " Medieval Warm Period" appear to have limited utility in describing trends in hemispheric or global mean temperature changes in past centuries. However, the timing of maximum glacial advances in these regions differs considerably, suggesting that they may represent largely independent regional climate changes, not a globally-synchronous increased glaciation. The Intergovernmental Panel on Climate Change Third Assessment Report (TAR) of 2001 described the areas that were affected:Įvidence from mountain glaciers does suggest increased glaciation in a number of widely spread regions outside Europe prior to the twentieth century, including Alaska, New Zealand and Patagonia. Several causes have been proposed: cyclical lows in solar radiation, heightened volcanic activity, changes in the ocean circulation, variations in Earth's orbit and axial tilt ( orbital forcing), inherent variability in global climate, and decreases in the human population (such as from the Black Death and the epidemics emerging in the Americas upon European contact ). At most, there was modest cooling of the Northern Hemisphere during the period. The Intergovernmental Panel on Climate Change Third Assessment Report considered that the timing and the areas affected by the Little Ice Age suggested largely independent regional climate changes, rather than a globally synchronous increased glaciation. One began about 1650, another about 1770, and the last in 1850, all of which were separated by intervals of slight warming. The NASA Earth Observatory notes three particularly cold intervals. The period has been conventionally defined as extending from the 16th to the 19th centuries, but some experts prefer an alternative timespan from about 1300 to about 1850. The term was introduced into scientific literature by François E. It was not a true ice age of global extent. The Little Ice Age ( LIA) was a period of regional cooling, particularly pronounced in the North Atlantic region. Global average temperatures show that the Little Ice Age was not a distinct planet-wide period but a regional phenomenon occurring near the end of a long temperature decline that preceded the recent global warming. For the most recent period that was much colder than present with significant glaciation, see Last glacial period.
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