GLOBAL WARMING: THE PAST CLIMATE

18,000 years ago the Earth was in the grip of an ice age. The climate was so cold that most of North America, Europe and Asia were covered by huge sheets of ice. Earth’s ice ages occurred around 270, 430, 670, 750 and 960 million years ago! During each of these periods, huge ice sheets advanced and retreated several times before the Earth’s climate warmed up again. Evidence – rock surfaces scraped clean of soil (Swiss Alps Remains of a huge ice sheet), deep parallel grooves in rocks, long thin parallel lakes, deposits of small mountains composed of soil, gravel and boulders (similar to deposits at the found at the mouths of current mountain glaciers). 1970’s the technique of "radioactive dating" was used to determine the age of the rocks.

200 million years age, the Earth’s climate was much different. The climate was so warm that semi-tropical plants grew in these same areas. In fact, the Earth’s long history includes periods of global cooling that have led to ice ages and global warming. How did we know about the Earth’s climate way back then?

#2. What can the past climate change tell us about possible climate change in the future?

Long periods of glaciation called "ice ages" were followed by periods of global warming during which the temperatures rose 4 – 6 degrees Celsius above the global average. These warm periods are called interglacials. We are now living in the largest known interglacial period. The ice age began retreating from NA 9000 – 12000 years ago when the climate began to warm. Clues left behind by ancient plants suggest that the temperature around the Great Lakes was about 2 degrees Celsius higher than it is today. Towards the end of this warm period, 900 AD, the climate in the Northern Hemisphere had become so mild that the North Atlantic Ocean was free of icebergs (this enabled explorers such as the Vikings to cross and colonize Iceland and Newfoundland in small ships – by today’s standards). Trees grew 100 km farther north than they do today and the Vikings were able to farm and support a community north of the Arctic Circle of around 5000 people. However, this was not to last as by the year 1500 to 1800 the permafrost and ice had taken over the rich farmland and the treeline was pushed southward. Sea ice filled the sea and the Vikings were forced to move south. THEREFORE, the Vikings were affected by naturally occurring changes in the Earth’s climate 800 years ago ----- yet the average global temperature decreased by ONLY ONE degree Celsius during this period! THIS period of time was known as the LITTLE ICE AGE!

The Great Ice Age (began 120 000 years ago and ended 10 000 years ago)

 

WHY DID THE CLIMATE CHANGE IN THE PAST?

SIX THEORIES OF CLIMATE CHANGE:

CHANGES IN THE EARTH’S POSITION: The Earth’s axis is currently tilted at an angle of 23.5 degrees. The tilt of the Earth’s Axis affects climates everywhere on our planet, especially in the polar regions. Over thousands of years, this tilt has varied from 22degrees to 25 degrees.

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Changes in Solar Radiation: An increase or decrease in the Sun’s output of radiant energy (infrared, visible or ultraviolet radiation) could lead to warming or cooling on the Earth. Increases in the Sun’s radiant energy output occur during periods of intense SUNSPOT ACTIVITY (magnetic storms on the Sun’s surface). Scientists feel that even a slight change of 0.5% in incoming radiation from sunspot activity could change the Earth’s climate significantly.

 

Changes in Ocean Currents Caused by Continental Movement:

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Changes in Reflection by Snow and Ice: feedback effect – more snow and ice means more radiant energy is reflected away from the Earth which means it could promote even more snow and ice.

Changes in Reflection by Particles in the Stratosphere: Cooling effect due to meteorite hitting the Earth and sending dust into the stratosphere for several years (reflecting incoming solar radiation). This is thought to have ended the reign of the dinosaurs 65 million years ago. Another great recent example of this was the explosion of Mount Pinatubo in the Philippines in 1992. The resulting eruption lowered the average global temperature by 0.5 degrees Celsius in 1992.

Changes in Concentrations of Greenhouse Gases in the Earth’s Atmosphere: As we have already discussed, more heat-trapping greenhouse gases means an increase in average global temperatures. The proof : ICE CORE SAMPLING whereby scientists removing cores of ancient ice and analyzing the bubbles of trapped air to determine how much carbon dioxide the Earth’s atmosphere contained. As you can see from the figure below, carbon dioxide levels and temperature rise and fall together. The research continues….

ICE CORE SAMPLING.www

Some recent projections suggest that global temperatures will change more in the next 100 years than they have in the past 10 000 years, THEREFORE, global warming could occur about 100 times faster than at any other time since the last ice age!

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email:  nick.tsioros@sac.on.ca

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