Global Air temperature from 1850 The time series shows the combined global land and marine surface temperature record from 1850 to The year 2007 was eighth warmest on record, exceeded by 1998, 2005, 2003, 2002, 2004, 2006 and 2001

Inter governmental Panel on climate change – IPCC- record Temperature rise of past one hundred years has been about C. Past 50 years experiencing a rise of 0.13 C per decade.

Temperature reconstruction Medieval warm periodLittle Ice Age

The ice-core temperature record from Vostok, Antartica Intrglacials Ice age

Temperature increase from last ice age Only 6 degrees Celsius temperature separate the modern climate from average ice age temperature

The Earth climate during the last 2 million years has been dominated by shifts between colder periods, known as Ice ages or Ice Ages have tended to last for up to 100,000 years. Interglacial periods have usually been much shorter in duration, at around 10,000 years in length. Glacial, and interglacial Period.

Last glacial period 130,000 years ago and ended (or at least subsided) within the last 16,000 years. Earth during the last Ice Age (at about the last glacial maximum, 16,000 B.C.).

Now - Interglacial period Today, the Earth's climate is again within an interglacial period, although the orbital theory of climate change, which explains the glacial-interglacial transitions, predicts that we may be coming towards its end.

CO 2 Versus Temperature Before Present (BP) years was used as the arbitrary origin of the age scale

Younger Dryas Period Towards the end of the last Ice Age, climate warmed, but then 12,000 years ago suddenly return to cold conditions. This cold episode lasted for about 1500 years and ended around years ago. This episode is now recognized as the YOUNGER DRYAS EVENT and is a prime example of dramatic and rapid climate oscillations.

Younger Dryas Period Younger Dryas

Younger Dryas Period The evidence comes from the reappearance of the Dryas flower in the Alps, which flourishes in glacial climates

YOUNGER DRYAS COLD EPISODE This cold episode is identified as the Younger Dryas cold phase, began with an ~7 o C drop in temperature, in only 20 years. The event ended as suddenly as it had begun with a dramtic increase in temperature of ~7 o C.

Thermohaline Circulation The thermohaline circulation, often referred to as the ocean's "conveyor belt", Thermohaline circulation is a very slow and extremely deep movement of water in the oceans around the world It links major surface and deep water currents in the Atlantic, Indian, Pacific, and Southern Ocean.

The Atlantic Conveyor Did the oceanic thermohaline circulation shut down during the Younger Dryas Period?

Atlantic Conveyor Shutdown As the great ice sheet of North America (Laurentide ice sheet) retreated, melt water was diverted from the Mississippi River to the St. Lawrence River North Atlantic ocean became capped with freshwater  not dense enough to sink  thermohaline circulation shut down for ~1000 yrs Could this happen again as a result of global warming?

Northern Europe The Younger Dryas was the most significant rapid climate change event that occurred during the last deglaciation of the North Atlantic region. It is now underdstood that this cooling event was experienced throughout the entire North Atlantic Region, the West Coast of Canada, and evidence of this event has also been found in the Southern Hemisphere.

What turns ice ages on and off?" The amount of sunlight changes due to the orbit of Earth about the sun and the tilt of Earth (23.5 degrees) on its imaginary axis.

Shape of the Earth’s Orbit The Earth’s orbit changes from circular to slightly elongate and back again about every 100,000 years.

Earth’s Tilt Its tilt changes between 22 and 25 degrees on a cycle of about 41,000 years. It is the tilt of Earth's axial rotation that creates seasons.

Earth’s Wobble Like a spinning top as it is slowing down, the Earth’s axis wobbles in a circle every 23,000 years. Because of this wobble, the Earth moves just a little bit more than one complete orbit each year

Combined Effect When these three changes in Earth's orbit—its shape, the tilt of the Earth's axis, and the wobble of the Earth's axis—are combined, they can explain why we get glacial and interglacial periods.