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quote:Originally posted by LaithWhen you say 'Longer term' how many years are you taking about? thousands? millions?
quote:The Maunder Minimum is the name given to the period roughly from 1645 to 1715 A.D., when sunspots became exceedingly rare, as noted by solar observers of the time. It is named after the later solar astronomer E.W. Maunder who discovered the dearth of sunspots during that period by studying records from those years. During one 30-year period within the Maunder Minimum, for example, astronomers observed only about 50 sunspots, as opposed to a more typical 40,000–50,000 spots. The Maunder Minimum coincided with the middle — and coldest part — of the so-called Little Ice Age, during which Europe and North America, and perhaps much of the rest of the world, were subjected to bitterly cold winters.Whether there is a causal connection between low sunspot activity and cold winters is the subject of ongoing debate. Some scientists believe that solar variation drives climate change more than carbon dioxide does (see global warming).
quote:Solar activityDuring the period 1645–1715, right in the middle of the Little Ice Age, solar activity as seen in sunspots was extremely low, with some years having no sunspots at all. This period of low sunspot activity is known as the Maunder Minimum. The precise link between low sunspot activity and cooling temperatures has not been established, but the coincidence of the Maunder Minimum with the deepest trough of the Little Ice Age is suggestive of such a connection . The Sporer Minimum has also been identified with a significant cooling period during the Little Ice Age. Other indicators of low solar activity during this period are levels of carbon-14 and beryllium-10 The low solar activity is also well documented in astronomical records. Astronomers in both Europe and Asia documented a decrease in the number of visible solar spots during this time period. Volcanic activityThroughout the Little Ice Age, the world also experienced heightened volcanic activity. When a volcano erupts, its ash reaches high into the atmosphere and can spread to cover the whole earth. This ash cloud blocks out some of the incoming solar radiation, leading to worldwide cooling that can last up to two years after an eruption. Also emitted by eruptions is sulfur in the form of SO2 gas. When this gas reaches the stratosphere, it turns into sulfuric acid particles, which reflect the sun's rays, further reducing the amount of radiation reaching the earth's surface. The 1815 eruption of Tambora in Indonesia blanketed the atmosphere with ash; the following year, 1816, came to be known as the Year Without A Summer, when frost and snow were reported in June and July in both New England and Northern Europe.
quote:The Medieval Warm Period (MWP) or Medieval Climate Optimum was an unusually warm period during the European Medieval period, lasting from about the 10th century to about the 14th century. It has been argued a better name would be the Medieval Climatic Anomaly. The MWP is often involved in contentious discussions of global warming and the greenhouse effect. Initial research on the MWP and the following Little Ice Age (LIA) was largely done in Europe, where the phenomenon was most obvious and clearly documented.It was initially believed that the temperature changes were global. However, this view has been questioned; the 2001 IPCC report summarises this research, saying: "…current evidence does not support globally synchronous periods of anomalous cold or warmth over this timeframe, 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".During this time wine grapes were grown in Europe as far north as southern Britain although less extensively than they are today (however, factors other than climate strongly influence the commercial success of vineyards; and the time of greatest extent of medieval vineyards falls outside the MWP). The Vikings took advantage of ice-free seas to colonize Greenland and other outlying lands of the far north. The period was followed by the Little Ice Age, a period of cooling that lasted until the 19th century when the current period of global warming began.The Medieval Warm Period partially coincides in time with the peak in solar activity named the Medieval Maximum (AD 1100–1250).In Chesapeake Bay, Maryland, researchers found large temperature excursions during the Little Ice Age (~AD 1400–1850) and the Medieval Warm Period (~AD 800–1300) possibly related to changes in the strength of North Atlantic thermohaline circulation. Sediments in Piermont Marsh of the lower Hudson Valley show a dry Medieval Warm period from AD 800–1300.Prolonged droughts affected many parts of the western United States and especially eastern California and the western Great Basin. Alaska experienced three time intervals of comparable warmth: 1–300, 850–1200, and post-1800 AD.A radiocarbon-dated box core in the Sargasso Sea shows that sea surface temperature was approximately 1°C cooler than today approximately 400 years ago (the Little Ice Age) and 1700 years ago, and approximately 1°C warmer than today 1000 years ago (the Medieval Warm Period). However, all the reconstructions, as shown above, appear to indicate that it was not.
quote:The Holocene Climate Optimum was a warm period during roughly the interval 9,000 to 5,000 years B.P.. This event has also been known by many other names, including: Hypisthermal, Altithermal, Climatic Optimum, Holocene Optimum, Holocene Thermal Maximum, and Holocene Megathermal.This warm period was followed by a gradual decline until about 2,000 years ago.For other temperature fluctuations see: Temperature record For other past climate fluctuation see: Paleoclimatology For the pollen zone and Blytt-Sernander period associated with the climate optimum, see: Atlantic (period) The Holocene Climate Optimum warm event consisted of increases of up to 4 °C near the North Pole (in one study, winter warming of 3-9°C and summer of 2-6°C in northern central Siberia). Northwestern Europe experienced warming, while there was cooling in the south. The average temperature change appears to have declined rapidly with latitude so that essentially no change in mean temperature is reported at low and mid latitudes. Tropical reefs tend to show temperature increases of less than 1 °C. In terms of the global average, the typical shift was probably between 0.5 and 2 °C warmer than the mid-20th century (depending on estimates of latitude dependence and seasonality in response patterns).
quote:Milankovitch cycles are the collective effect of changes in the Earth's movements upon its climate, named after Serbian geophysicist Milutin Milankovi#263;. The eccentricity, axial tilt, and precession of the Earth's orbit vary in several patterns, resulting in 100,000 year ice age cycles of the Quaternary glaciation over the last few million years. The Earth's axis completes one full cycle of precession approximately every 26,000 years. At the same time, the elliptical orbit rotates, more slowly, leading to a 22,000 year cycle in the equinoxes. In addition, the Earth's tilt relative to the Sun changes between 21.5 degrees to 24.5 degrees and back again on a 41,000 year cycle. The Earth's axis today is tilted 23.44 degrees relative to the normal to the plane of the ecliptic.The Milankovitch theory of climate change is not perfectly worked out; in particular, the largest response is at the 100,000 year timescale, but the forcing is apparently small at this scale – see Ice age for more discussion. Various feedbacks (from CO2, or from ice sheet dynamics) are invoked to explain this discrepancy.Milankovitch-like theories were advanced by Joseph Adhemar, James Croll, Milutin Milankovi#263; and others, but verification was difficult due to the absence of reliably dated evidence and doubts as to exactly which periods were important. Not until the advent of deep-ocean cores and the seminal paper by Hayes, Imbrie and Shackleton "Variations in the earths orbit: pacemaker of the ice ages" in Science, 1976, did the theory attain its present state.
quote:Originally posted by JimBobBut what about the possibility of the warmenr temps. causing all the Methane hydrate in the oceans to melt, all the methane exters the atmosphere and PRESTO, grenhouse? Is this going to happen?
quote:Originally posted by ukmickywhat they did was look at the warm periods in the earths history which could be tested through the melting core samples of ice to release the traps gases. They wanted to see if any of the worlds periods of global warming were caused by or affected by the release of methane hydrates. They found no evidence of elevated methane in the atmosphere during any period of global warming.
quote:Originally posted by JimBobFirst, to clarify one issue - Water does not lubricate faults. Not even oil can do it. Lift the hood (bonnet) of a car to get an idea of the effect of a small amount of force on either substance.
quote:Originally posted by ukmickyThere was also a program last week on sky digital bbc 4 channel where they were looking into global warming and they looked at the most recent historical periods . They did the same thing and tested the gases released from melted ice taken from core samples looking for evidence of raised methane and found nothing. So their must be someway which they can test for it.
quote:Originally posted by JimBobMichael is correct. Inclusions in the ice cores contain the atmosphere of the earth when the ice around such inclusion was formed. These inclusions are easily analysised by normal conventional methods and it is positive proof of atmosphere composition. Rigorous testing and discussion of the value of the gas analyisies by concerned scientist, both practical and theoretical, has allowed gas inclusions to become the benchmark for scientif analysis of ancient atmospheres.
quote:molecule of methane consists of four hydrogen atoms and one carbon atom. Carbon comes in several isotopic varieties, with different weights. Most of it is an isotope known as carbon-12 (12C), but there is always a smattering of a heavier isotope, 13C, mixed in. Because 13C is heavier, organisms tend to absorb it less readily than they do 12C. This means that carbon which comes from a plant, or a swamp-dwelling bacterium that is digesting that plant, will have less 13C in it than did the carbon in the atmosphere from which the plant drew its sustenance. However, methane from undersea hydrates has an even bigger 13C deficit than that from surface bacteria. This is because it has been generated by bugs called archaeobacteria. Since this “deep biosphere” is such an inhospitable environment, these archaeobacteria need to be even more discriminating in their choice of carbon isotopes than organisms at the surface. So looking at the amount of 13C in bubbles formed at the end of the ice age should help to resolve the issue of where the methane came from.
quote:Originally posted by VAlibrarianBut when I stir pepper into a stew and notice a more pungent taste, I think I know why.
quote:Originally posted by VAlibrarian To me, the data represents a danger that my great-grandkids (if any) will inherit a world of higher temperatures and a higher likelihood of both floods and droughts.
quote:Originally posted by JimBobNot quite accurate. 10,000 years ago earth was cooloer than it is now and there was much less desert than now. All the area of central asia was much more lush: areas that are now the worst deserts of the world (such as the Taklamakan) were irrigated, had no erosion and no sand. Today you die in them. This is true for all of Africa as well. There was no Sahara Desert, no Namibian Desert, etc. All of these deserts were well watered, had a diverse fauna and flora as well as human habitation.The warming of the earth during this interglacial is real. The question is whether or not man has accelerated this process so: Again I ask ---
quote:MADISON -- Water would seem like a mirage today in the sweltering Sahara Desert, but climate researchers at the University of Wisconsin-Madison are finding the ancient Sahara was a wetter, greener place than ever imagined.Writing in today's (Dec. 19) edition of the British journal Nature, UW-Madison climatologist John Kutzbach and colleagues report that the Sahara and Sahel regions of northern Africa were much wetter 12,000 to 5,000 years ago than earlier climate models predicted.A slight shift in the earth's orbit forced those changes, causing stronger summer monsoons to sweep through the region. This naturally produced more vegetation and increased water content in the soil.
quote:The earliest humans in the area were Palaeolithic hunter-gatherers, who lived in the Fazzan between about 400,000 and 70,000 years ago. They survived by hunting large and small game in a landscape that was considerably wetter and greener than it is now. A prolonged arid phase from about 70,000 to 12,000 years ago apparently drove humans out of the region, but then the rains returned – along with the people. Around 5,000 years ago the climate began to dry out again, but this time people adapted by developing an agricultural civilization with towns and villages based around oases. This process culminated with the emergence of the Garamantian society in the first millennium BC.
quote:Originally posted by another_someone... Historic data, as well as common sense, associates widespread drought with global cooling. Drought is not caused by heat but by lack of water, which infers lack of rainfall, which when taken on a global scale will relate to reduced evaporation caused by lower temperatures.George
quote:Although arid, the Sahara was not a desert until recently
quote:By deifnition, I live in one of the hot deserts, the Sonoran Desert - average rainfall less than 15 cm of rain a year and high heat. It is to be 100 degrees F and above this weekend. I live amid grass, deer, cougars, trees including pine trees, rabbits, and cattle in profusion, etc, etc. Arid does not mean void of life.
quote:Originally posted by VAlibrarianI understand that this makes me a crackpot in the eyes of a few, but I am reminded of the physician (his name escapes me) who noticed 200-odd years ago that women in hospitals were dying of infection at a much higher rate than women giving birth at home. When he hypothesized that doctors were passing infection from one mother to another while attending childbirth without washing their hands, he was kicked out of the hospital and publicly called a buffoon. The women continued to die for a few years until he was proved correct.
quote:Originally posted by VAlibrarianIn the meantime, sell that property in south Florida while the market is still high. When the flooding from global warming's increase in sea levels starts, insurance rates will go up and nobody will want to buy your house.