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One point also should be raised, that is not in this rather interesting discussion thread, is volcanism and the junk tossed up in to the atmosphere can accelerate climate change as well. If I remember my geology, there was a volcanic activity about 20 to 23 million years ago west as south of Brisbane. Known as the Mount Warning Shield Volcano, this volcanic mountain rose 2 km., the highest point anywhere on the Australian continent in the last 250 to 500 million years. The size extended 100 kilometres, spreading from Byron Bay, Mount Tamborine and Lismore. The caldera is known as the Tweed Volcano, whose size is 40 km. across and about one kilometre deep. It remains one of the biggest volcano we know of! http://www.iceinspace.com.au/forum/....s/scared14.gif
Such volcanic activity would have catastrophic influence on the southern climate, especially as the latitude of Australia was closer to just south of where Tasmania is today
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Yep, know all about Mt Warning
. Nice place to hike and the geology is spectacular
. However, volcanism such as the one that is represented by Mt Warning isn't as deleterious on the climate as you might think. Volcanoes like Mt Warning are not as violent nor as immediately influencing as your typical volcanoes such as Krakatoa, Tambora etc. The reason why Mt Warning was as big as it was (it was quite a bit taller than Mt Kosciusko) is because the mountain is made up of vast sheets of basalt that were made up of many lava flows. The volcanism you see there is the same as the volcanism you get in Hawaii. It's very extensive, can last a long time for each individual eruption (many years, in fact), but is relatively quite. Most of the emissions from a shield volcano are water vapour, with some CO2, CO, H2S and other gases. A lot is put up into the atmosphere, but it occurs over a long period of time.
The volcanism we have to be really worried about is the type that is present in areas such as Yellowstone, Snake River, Lake Toba etc. This type of volcanism is similar to your more typical volcanoes, Acidic and Calc-Alkaline, and the explosion in these volcanoes is rather abrupt and can be extremely violent. They tend to pour out vast quantities of volatiles in a short period of time, along with vast quantities of ash. However, unlike your typical volcano, these ones are on a vastly larger scale. The whole Mt Warning volcano would disappear inside the caldera at Yellowstone. When these fella's erupt, it's goodnight starlight time. Your typical supervolcano (as they are called) can erupt anywhere from 2500 to 20000km^3 of rock and ash, most of it blasted into the atmopshere and trillions of tons of volatiles. Last time Yellowstone erupted (650Ka....and now we're overdue by some 40000 years), it blasted 2500km^3 of ash and rock into the sky....covered the US right out to the distance of Phoenix, Az, in a metre of ash!!!!. In that same eruption, a complete range of mountains, over 80kms in length, many over 7000 feet high, disappeared in a few seconds...they slipped into the caldera. Lake Toba (on Sumatra) was even more important to us, as it's effects may have nearly sent our species into oblivion. It blasted 2000km^3 of dust and ash into the atmopshere about 75Ka ago. It's been estimated that the eruption reduced us down to about 500-2000 individuals...however, there is still some controversy about this.
If Yellowstone or another supervolcano erupted today, we'd be in for a very rough time....it would kill many millions with it's immediate and after effects....more so with its after effects. An eruption like that would drastically change the climate, and almost overnight. By the time the northern winter came along (if it erupted in the early to mid summer), it would already be pretty cold and it would only make things worse. The USA would just be a memory...they'd be FUBAR. Canada and Mexico would also be in quite a lot of trouble as well. The rest of us would also be in for some very heavy going too. So, let's hope we never see such an eruption.