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Blowin' in the Wind, Issue #047 What is Globle Warming - October 1, 2007
October 01, 2007
Ask What is Globle WarmingIf you've paid much attention to the news, " What is Globle Warming " should be familiar. In a nutshell, the Earth's average mean land-based temperature has been rising, and there's a great deal of controversy about the cause, whether or not it's an impending disaster, or if human activity is at fault. And can we somehow avert it?
A (pre)historic perspective.Since roughly 1900, the most commonly measured mean average temperatures in the northern hemisphere have risen by close to one degree Centigrade, with the bulk of this temperature rise occurring in the years prior to 1945. From 1800 to 1900, the temperature climbed by roughly another degree Centigrade, and it's estimated (due to a lack of detailed and reliable records) to have risen by about the same amount in the 18th Century. The point of this is to put global warming in perspective. Prior to the 18th Century, deducing what the global temperatures were is a bit trickier; it usually involves interpolating geographically contiguous historical accounts with natural records like tree rings and geological records of snow pack and ice melt. Prior to the Renaissance (1300 to 1650), tracking global temperature gets even more tenuous, with the use of crop yields, coupled with archeological records of what was grown and what was eaten in a given area. (Due to animal-driven agriculture and transport sectors, it's a reasonable presumption that foods were consumed within 30 to 60 miles of where they were grown until the 18th century.)
What these records show is that there was a two-century period called the Little Ice Age, and a four-century span, from roughly 1000 AD to 1400 AD, called the Medieval Warm Period. Before the Medieval Warm Period was a cold oscillation (and reduced crop yields), and prior to that, the Classical Climate Optimum during most of the Roman Era.
So, contrary to much of the portrayal on the issue – that we're causing the Earth to heat up in ways unprecedented in its history – some of the research uncovered show that we are, just now, reaching the lower boundary temperatures of the Medieval Warm Period. Assuming we continue with temperature rises of one degree Centigrade per century, we may hit the temperatures of the Classical Climate Optimum around 2120 AD.
What causes global warming?The two chief candidates for a "smoking gun" for global warming are anthropogenic (human caused) releases of carbon dioxide (CO2), and variations in the sunspot cycle, which reflect the Sun's magnetic field, which protects the upper atmosphere from cosmic rays. Long term global climate fluctuation comes from subtle variations in the eccentricity of the Earth's orbit and precession of its axial tilt called the Milankovitch Cycles (pronounced Milankovic Cycles), and it's this cycle that sets out the march of glaciers and ice ages, which typically run for a few hundred thousand years with a roughly twenty-thousand year interglacial period.
What's the impact of global warming?
Global warming (more accurately, global climate change) affects everything from weather forecasts to crop yields to ocean sea levels. While it's common to blame hurricane seasons where there are a larger than usual number of hurricanes on global warming, most meteorologists stop short of that claim. What is globle warming to bring about? It could alter the agricultural regions of the world around as rain patterns shift, and temperatures change, and may be contributing to desertification in a lot of areas of the world.
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