Nature Notebook: Climate Report – One for the Ice Ages

Ice on lake

By Dylan Cooper, columnist

In last month’s column, we looked at 2020 weather data and past climate data. What if we looked back in time even further? Modern weather technology only stretches back a century at best. Some temperature data goes back a couple centuries. We have testimonies of the weather conditions in the form of written books and other accounts for a couple thousand years. Tree rings and soil layers also stretch back a few thousand years. To get back any further you have to dive deep into scientific studies of geology, molecular composition and aging, or archaeology and paleontology. Carbon dating gets us back about 55,000 years currently. Ice cores from polar regions tell us clues to 100,000 years ago. Geologic formations tell us millions of years of climate history.

The coldest climate that we can tell occurred from these scientific records happened between 600 million and 750 million years ago. They think ice stretched from the poles all the way to the equator. Scientists continue to debate the causes that drove the planet into and out of this deep cold spell but most evidence points toward volcanic activity. There is evidence here in Virginia near Charlottesville to support this theory. Near Sharp Top Mountain they found diamictite which was conglomerate rock formed from 750 million year old glacial sediments of varying sizes of stones that have been compressed over time into the consolidated rock outcroppings seen today.

The most recent ice age may have been the coldest period in the last 500 million years, and it occurred from 2.6 million years ago until just 11,000 years ago. Some say we’re still technically in this ice age, just in an interglacial period. The furthest extent of this most recent glacial period was an ice sheet that came down into Ohio and Pennsylvania, pressing the land and bedrock down underneath it but bulging it up and out in front. The land that was pushed up is now subsiding with the long-ago retreat of the ice sheet. That land area includes the eastern part of Virginia which is why sea level rise is accelerating faster there than most parts of the world. 

Speaking of sea level, the glaciers during the last ice age had so much water locked in them that the Atlantic Ocean was an astonishing 400 feet lower than it is today. The Chesapeake Bay was mostly dry and the eastern shore extended another 75 miles eastward. 

During the last ice age, Virginia was basically a tundra-like landscape, sort of like what the middle/southern parts of Canada are today but with less snow. Large mammals were common like the eastern elk, wood bison, white-tailed deer, giant stag-moose, dire wolves, and wildcats. Even mammoths and giant ground sloths roamed Virginia at that time. Of course, most of these have gone extinct, either with the changing climate or human hunting pressure. Evergreen species like spruce and fir dominated the landscape. The red spruce is actually still holding on to some pieces of the cooler, moist high ground in VA and WV, an enduring relic of this last ice age.

There are even lasting artifacts of the last ice age here in Page County. Along the Massanutten Mountain range are several “block fields” or massive piles of broken sandstone. These boulder chunks, called talus, broke off during the last ice age when there were severe freeze-thaw cycles working to break apart the bedrock outcrops above these areas. We know the talus fields are fresh enough to have been from that time period because of the sharp and angular characteristics of these rocks meaning they haven’t experienced the amount of weathering like the rocks down in our valleys have.

There are many feedback loops that affect our planet’s climate and probably even more that we don’t even know about yet. The simplest feedback loop to explain deals with the phase change of water, the most abundant substance on earth. Water currently covers about 71% of earth’s surface and 96.5% of that water is in the oceans. Currently, only about 1.74% of the earth’s water is locked up in its solid phase of ice caps, glaciers, and permanent snow. These solid phases are the most reflective of sunlight back into the atmosphere. On the other hand, water in its liquid phase absorbs more sunlight and thus heats up quicker than ice. Therefore, a planet that is mostly liquid water will heat up faster than a planet that’s mostly ice, given other variables are held constant. A warming planet leads to melting ice caps which means more liquid water to absorb more heat and in turn leads to more ice melt. That is a feedback loop. The same feedback cycle is true of a planet that is cooling which leads to more ice formation, more reflection of sunlight, and thus cooling temperatures even further. 

Obviously these water-related feedback loops aren’t the only main drivers of our planet’s climate or else earth would be either one planet-sized frozen block of ice or one global steaming pool of water. Cycles in solar radiation, magnetic field reversals, volcanic activity, plate tectonics, greenhouse gases, ozone, microbial life, and the earth’s tilt, wobble, and orbit have changed the climate on this planet many times over in its 4 billion year history. 

Exciting new research found from carbon-dating a 1,700 year old tree trunk that lived 42,000 years ago in present-day Australia shows that the earth’s geomagnetic field weakened and even flipped during that period. When the magnetic field weakens (as it had during this event to 6% of current levels), it allows for more radiation, solar flares, etc. to reach the earth’s surface. This can have a dramatic effect on climate, plants, and animals. This reversal only lasted about 1000 years but it likely caused some mass extinctions. It just so happens that this time period aligns with when most large land mammals disappeared, as did our genetic cousins, the Neanderthals, in present-day Europe. This may give us a slight cause for worry because the North Pole has been moving at about one kilometer per year recently and there is data showing the magnetic field is weakening. There is simply no telling when the next pole reversal will happen, though estimates put it thousands of years away.

Dylan Cooper is a Page County native and graduate of Luray High School and Virginia Tech. He is a stream restoration specialist for a local non-profit and a registered professional engineer in the state of Virginia. Avid outdoorsman and ardent environmentalist, he resides in Luray with his wife and dogs.  

Email: [email protected]

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