I really do love good science and good engineering:
Google Engineers Admit Renewable Energy Will Never Slow Climate Change
August 2014: Swiss glaciers receding unearths 4,000 year old forests grew underneath in prior times: "Dr. Christian Schlüchter’s ... report might have been more conveniently dismissed by the entrenched global warming establishment were it not for his distinguished reputation as a giant in the field of geology and paleoclimatology who has authored/coauthored more than 250 papers and is a professor emeritus at the University of Bern in Switzerland."
Same story, second verse: October 2013, Alaska/northwestern Canada: "Retreat of the Mendenhall Glacier reveals the remains of trees which grew more than 2,000 years ago: "The most recent stumps she’s dated emerging from the Mendenhall are between 1,400 and 1,200 years old. The oldest she’s tested are around 2,350 years old. She’s also dated some at around 1,870 to 2,000 years old.
"In Glacier Bay, Connor and other researchers have found evidence of ice advances occurring more than 5,000 years ago. They’ve also documented the glacial advance between 1724 and 1794 A.D. that pushed Huna Tlingit off their land, and written a paper incorporating those cultural and geographic histories. In that paper they cite Tlingit histories recorded by Richard and Nora Dauenhauer as saying that glacier was growing and advancing “faster than a running dog.”...Some of the ages of these trees suggest the Roman Warm Period may have occurred at the same time as an Alaskan Warm Period."
More on that same story, told in September 2013: "An ancient forest has thawed from under a melting glacier in Alaska and is now exposed to the world for the first time in more than 1,000 years. Stumps and logs have been popping out from under southern Alaska's Mendenhall Glacier — a 36.8-square-mile (95.3 square kilometers) river of ice flowing into a lake near Juneau — for nearly the past 50 years. However, just within the past year or so, researchers based at the University of Alaska Southeast in Juneau have noticed considerably more trees popping up, many in their original upright position and some still bearing roots and even a bit of bark, the Juneau Empire first reported last week...[scientists] tentatively identified the trees as either spruce or hemlock.."
"Western hemlock thrives in a mild, humid climate where frequent fog and precipitation occur during the growing season...Mean annual temperatures range from 0.3° to 11.3° C (32.5° to 52.3° F) on the coast...Observed mean July temperatures lie between 11.3° and 19.7° C (52.3° and 67.5° F) along the coast...Mean January temperatures reported for [the coast are] -10.9° to 8.5° C (12.4° to 47.3° F)...Recorded absolute maximum temperature for the coast is 40.6° C (105.0° F) [and] minimum temperatures tolerated by western hemlock are -38.9° C (-38.0° F) for the coast."
Could it be black spruce? "The climate for black spruce can be characterized as cold with a moisture regime varying from humid to dry subhumid. Mean annual temperatures range from 7° C (45° F) in the southern areas to -11° C (13° F) near tree line in central and western Canada. Average January temperatures range from -30° C (-22° F) in northwestern Canada and Alaska to -6° C (21° F) at the southeastern edge of its range. Average July temperatures range from 16° to 24° C (60° to 76° F) in the main part of the range of black spruce and from 10° to 27° C (50° to 80° F) in extreme locations. The extreme low temperatures range from -62° to -34° C (-79° to -30° F), the highs from 27° to 41° C (80° to 105° F)."
Or White spruce, also known as Canadian spruce? "[It] grows under highly variable conditions, including extreme climates and soils...In the north, the position of the tree line has been correlated to various factors, including the 10° C (50° F) isotherm for mean July temperature...At the northern limit of the species' range, climatic extremes are significant. For example, -54° C (-65° F) in January and 34° C (94° F) in July were recorded extremes in one study area. Mean daily temperatures of -29° C (-20° F) for January are recorded throughout the species' range in Alaska, Yukon, and Northwest Territories, while mean daily July temperatures range from about 21° C (70° F) in the extreme southeastern area of distribution to 13° C (55° F) throughout much of Alaska and Canada."
Equation: At one point in time, then, it had to have been between -79° F to 105° F for black spruce to grow there, between -38.0° F and 105.0° F for Western hemlock to grow there, or -65° F and 94° F for White spruce to grow there. And then, get covered up by glaciers so fast, they were preserved for the past 1,000 to 2,000+ years.
May 2013, Alberta, Canada: "Scientists revive ‘Little Ice Age’ plant frozen 400 years under glacier ice: "Scientists in Alberta said this week they’ve revived a plant that was trapped under glacier ice for some 400 years or more, discovered during an exploration of Canada’s Teardrop Glacier in 2007....The organism is an ancient moss in the category of bryophytes, non-vascular plants that grow on land and typically converge on rocks, soil or tree trunks. They noticed the plant sticking up from some melting ice and took a sample, thinking they’d just discovered something that has not lived on the planet in hundreds of years...Sure enough, they were right: the moss was frozen solid during the “Little Ice Age,” a period of tremendous upheaval in Europe between the 14th and 19th centuries. Back in the lab at the University of Alberta, biologist Catherine La Farge re-planted some of the moss and, to her surprise, watched as it grew."
Also covered by National Geographic.
Bryophytes are "Surprisingly, Arctic liverworts are not so cold
resistant. Among the nine species tested by Biebl (1968), seven were mostly dead at -16ºC (3.2º F), with only Lophozia hatcheri and Chandonanthus setiformis surviving well. The moss Aulacomnium turgidum also survived at -16ºC (3.2º F). All species survived -6ºC (21.2º F). But these were July responses in Greenland; a quite different picture might emerge in winter. On the other hand, all of them survived up to 42ºC (107.6º F) for half an hour, but twelve-hour exposures killed parts of most of them, the same seven, at 38ºC (100.4º F)...This supports the hypothesis that low temperature survival is coupled with high temperature survival." "[B]ryophytes can survive at sub-zero air temperatures by their own ability to alter the temperature. Lewis Smith (1988) found that in Antarctica the temperature at the surface of a Schistidium cushion (Figure 5) could vary from -9.2°C to 42.8°C (15.44° F to 109.2° F) on a single day in January..."
So arctic (as opposed to tropical) bryophytes seem to generally grow and thrive when temperatures are between 21.2º F and well below 100.4º F.
It's hard to find concrete statements about how cold it must be to form and sustain glaciers or ice sheets, as there are varying kinds of glaciers, but one source states that "Ice shelves are always stable under mean annual temperatures of −9° C (15.8° F), but never stable above −5° C (23° F)". If you can glean an understandable number from this paper, good luck to you.
October 2007, Garibaldi Provincial Park, about 40 miles north of Vancouver, British Columbia: "Melting glaciers in Western Canada are revealing tree stumps up to 7,000 years old where the region's rivers of ice have retreated to a historic minimum, a geologist said today...The pristine condition of the wood, he said, can best be explained by the stumps having spent all of the last seven millennia under tens to hundreds of meters of ice. All stumps were still rooted to their original soil and location."
The simple point is that none of those trees or mosses would have grown there in the first place, had those areas never once been temperate enough to allow their growth. None of those trees or mosses would have grown there if the areas were always glacial masses. The cycle may be just that, a cycle the earth goes in, repeatedly, over thousands of years.