Don,
On middle age warming: "The dedicated minority who insisted that there was no global warming problem promptly attacked the calculations. For example, in 2003 a few scientists argued that the Medieval Warm Period had been as hot as the 20th century. But other climatologists, looking at data for the entire world, found a scattering of warm and cold periods in different places at different times, not at all comparable to the recent general warming. Like the temporary cooling of the 1960s, the famous Medieval Warm Period was probably seen only in parts of the Northern Hemisphere.(48*) (For more on global temperatures before the 19th century, see the essay on solar influences.)" On Antarctica: "No less convincing, Arrhenius at the turn of the century, and everyone since, had calculated that the Arctic would warm more than other parts of the globe. That was largely because less snow and ice would reflect less sunlight back into space. (This effect would not be expected in Antarctica, with its colossal year-round ice cover, and in fact warming was not seen there except around the coasts and on the long peninsula that projected beyond the ice sheet). Arctic warming was glaringly obvious to scientists as they watched trees take over mountain meadows in Sweden and the Arctic Ocean's ice pack grow ever thinner. Alaskans and Siberians didn't need statistics to tell them the weather was changing when they saw buildings sag as the permafrost that supported them melted." And: "In February-March 2002 the Larsen B ice shelf, a mass of floating ice some 220 meters thick and larger than Rhode Island, broke up into icebergs. The flow of glaciers held behind the ice shelf accelerated. The ice shelf had probably existed since the last ice age. This was only the largest in a 30-year series of retreats of ice shelves along the Antarctic Peninsula, the only part of the continent that scientists had predicted would be affected soon by greenhouse warming. I wonder if this occured after one of the papers you listed was published. On the southern hemisphere: "Meanwhile in 1975, two New Zealand scientists reported that while the Northern Hemisphere had been cooling over the past thirty years, their own region, and probably other parts of the Southern Hemisphere, had been warming.(29) There were too few weather stations in the vast unvisited southern oceans to be certain, but other studies tended to confirm it. The cooling since around 1940 had been observed mainly in northern latitudes. Perhaps cooling from industrial haze counteracted the greenhouse warming there? After all, the Northern Hemisphere was home to most of the world's industry. It was also home to most of the world's population, and as usual, people had been most impressed by the weather where they lived." I could not find where your link showed growing ice in Antarctica. Is this like Ron's post that showed a slight increase after a decade of decline? The Southern Ice Sheets are different and they do say it would have a bigger effect in the north (changing Albedo). Antarctica Ice Sheets may be adversely affect by a modest rise in sea level. I will close: "However, "fingerprints" were found that pointed directly to greenhouse warming. One measure was the difference of temperature between night and day. Tyndall had pointed out more than a century back that basic physics declared that the greenhouse effect would act most effectively at night, as the gases impeded radiation from escaping into space. Statistics did show that it was especially at night that the world was warmer." Erik Erik,
"BTW: A little perspective on warming during middle ages. This is
evidence
that the warming is greater today. Note the mention of Glaciers that survived "thousands of years"."
That is Mann's data and there is a lot of evidence it is incorrect (over 100 peer reviewed articles) and that there was more warming during the Medieval Warm Period and hence less ice in the arctic.
See http://www.springerlink.com/content/g15qv13t1v12np00/
First when you say polar you mean north polar since the ice in Antarctica has actually increased. See
http://icecap.us/index.php/go/joes-blog/proof_we_are_causing_polar_warming_m elts_away_in_the_cold_light_of_reality/
and
http://www.co2science.org//articles/V5/N40/C3.php
Don
-----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of erikhansen@TheBlueZone.net Sent: Thursday, March 12, 2009 10:24 AM To: Utah-Astronomy@mailman.xmission.com Subject: [Utah-astronomy] 20th Century Temp Trends.
Hi All,
The below is the intro to an article about the history of temp changes. The graph Ron showed still showed that the ice sheets are at the 2nd smallest extent. IE: Only slightly greater than 2007.
"Tracking the world's average temperature from the late 19th century, people in the 1930s realized there had been a pronounced warming trend. During the 1960s, weather experts found that over the past couple of decades the trend had shifted to cooling. With a new awareness that climate could change in serious ways, many scientists predicted a continued cooling, perhaps a phase of a long natural cycle or perhaps caused by human pollution of the atmosphere with smog and dust. Others insisted that the effects of such pollution were temporary, and humanity's emission of greenhouse gases would bring warming over the long run. This group's views became predominant in the late 1970s. As global warming resumed it became clear that the cooling spell (mainly a Northern Hemisphere effect) had indeed been a temporary distraction. When the rise continued into the 21st century with unprecedented scope, scientists recognized that it signaled a profound change in the climate system."
http://www.aip.org/history/climate/20ctrend.htm
BTW: A little perspective on warming during middle ages. This is evidence that the warming is greater today. Note the mention of Glaciers that survived "thousands of years".
"Scientists were still less able to answer the question of whether climate change was gradually melting the rest of the world's glaciers and ice caps, or instead was adding snow to them. In "those huge areas where little or no information is available," an expert explained in 1993, "almost anything might be happening." But in 2005 a survey of mountain glaciers around the world found that most of those for which historical records existed had been shrinking since 1900. Some that had survived for many thousands of years were vanishing, a striking sign of unprecedented climate change.Experts could only speculate how far this might affect sea level, especially if it were counteracted by the increased snowfall that some models predicted global warming would bring in the remote dry highlands of Antarctica.(26*)"
Erik
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