I recently finished reading an interesting book, After the Ice Age: The Return of Life to Glaciated North America
by E. C. Pielou
. (I'm researching what parts of the Earth looked like for humans at the end of the last glaciation, when the big ice started melting and the sea levels started rising.)
In researching Ice Ages, I learned a number of interesting things. One is that we are still in the Quaternary Ice Age; we are merely in an inter-glacial within the Ice Age. The Ice Age will not end until the continents stop surrounding the north pole and the Antarctic continent moves off the south pole. That's a very long time in the future. In the meantime, glacials and inter-glacials are governed (mostly) by Milankovitch Cycles
, though the changes in Earth's orbit affect temperature in complex ways. Note that neither element (plate tectonics, orbital cycles) is under human control. There will
be another glaciation, and there is not much we can do about it.... except maybe dump lots of CO2
in the air.
But wait, isn't everyone worried about anthropogenic global warming (AGW)? Well, yes... and no. The warmest period of the current interglacial, the Holocene Climate Optimum (aka hypsithermal)
, ended about 5000 years ago, about the time of Egypt's Old Kingdom, which developed during the warm, wet period. It's cooler now than it was during the Optimum; in North America, various temperature-sensitive ecosystems were several hundred kilometers north of where they are now. Right now, we might warm back up to that temperature; the main thing that climate scientists are concerned about is the rate of warming, which seems greater than what has happened before. On the other hand, sudden climate changes don't show well in the fossil record; the resolution isn't that good. We know it warmed very rapidly at the start of the Optimum.
The Little Ice Age
may have been the start of the next round of glaciation (the "neoglacial")--if so, it was reversed right around the time industrialization started dumping CO2
in the air in a big way, about 1850. AGW may well be what is staving off the next glaciation; we don't know enough yet. What we do know is that panicking that "global warming will destroy the world!!1!!" is stupid hysterical nonsense.
Another glaciation, on the other hand... well, look at the last glaciation. There is nothing quite as devastating to an ecosystem as grinding it under a few hundred feet of ice--not even strip-mining for coal is that bad. Nothing lives on an ice sheet, and nothing bigger than microbes and algae lives under it. (Although there are cave refugia under the rock under the ice where cave lifeforms carry on...). The sheer weight of a continental ice sheet depresses the continental crust under it (this will be important later); the presence of a continental ice sheet alters the weather in major ways, as icy catabatic winds howl off the ice sheet to sweep the lands surrounding the ice (it also carries dust for hundreds of miles, piling up massive loess deposits beyond the ice). All that water locked up in a continental ice sheet is no longer part of the water cycle; the whole planet becomes drier and more arid. Polar deserts and tundra surround the ice sheets; boreal forests persist in humid areas of what used to be the temperate zone. The rest of the mid-latitudes are cold steppe. Temperate forests get pushed back to the humid sub-tropics; the tropics become more arid and rainforests nearly vanish, replaced with steppe; the old steppe becomes deserts. The Sahara desert enlarges far beyond the current nightmares of desertification. Alpine and tundra life persists at the edge of the ice, or in isolated refugia along the coast or on nunataks. The sea-level falls 100-120 meters
The end of the glaciation was also devastating. The great ice sheets slowly thinned and melted back, revealing land scrapped bare of soil except for the layer deposited by the retreating ice. Vast icy lakes of melt-water formed at the melting edges of the ice sheets, because the land was still depressed from the weight of the ice. Beyond the ice sheets, the land had bulged upward in isotatic reaction; as the crust rebounded from the weight of the ice, the land beyond the ice sheets sank back down to its normal position, adding isostatic sinking to the eustatic sea level rise from the melting ice. (Because the bordering crust had bulged upward, at first the glacial melting didn't raise the sea levels much...then it suddenly did). As the crust that had been under the ice sheet rose, the proglacial lakes switched drainage routes, and/or drained away--the vast freshwater sea that covered what is now the Great Lakes and most of Ontario eventually settled into the Great Lakes; the inland freshwater seas further west shrunk into the Great Bear and Great Slave lakes of the present day. (Fish populations re-populated the interior because of these lakes and drainage switching around, as fish can't walk to new lakes or rivers). Plants slowly migrated northwards, from the south or from refugia, first the pioneers that could grow in rock dust, sand and gravel, later the plants that needed damp, organic-heavy soil to root in. Animals moved in as fast as the plants they could browse on, though the big carnivores could cross sea ice and barrens in search of prey (Newfoundland is top-heavy with carnivore species because of this). Humans moved in where there was sufficient food, and hunted mammoths.
The sea level rose and rose and rose as the great ice sheets melted and the crust rebounded, up to 120 meters in some places. Beringia flooded, and became Siberia and Alaska. The dry land ('Doggerland') between the British Isles and Scandanavia floods, becoming the North Sea and the English Channel. Much of Southeast Asia becomes the string of large and small islands that we are familiar with today, instead of the low-lying continental mass it was during the glaciation. The face of the world changed.
Note that I am not arguing that global warming is happening--that it is undebatable fact, measured by satellite for several decades now, and by buoy and ground station for over a century. We have the numbers. There is a correlation with global CO2
levels. What we don't know: how hot does it get before Earth's feedback mechanisms kick in and damp it down? The oceans lock up and deposit excess CO2
in the form of carbonates via the Carbonate-silicate weathering cycle
; the hotter it gets, the faster that happens, until enough carbon dioxide is pulled out of the atmosphere to cool things down to Ice Age glaciation levels again.
Panic and hysteria help no one and nothing, except someone with an agenda that requires people to react without thinking. They certainly don't solve the problem of AGW...if it is a problem that can be solved, or even needs to be solved. Climate does change, it has changed drasticly in the past, it will change in the future, it is changing now. Things will never be exactly like they were last Tuesday, that's just not how the Earth works.