Global Air temperature from 1850

The time series shows the combined global land and marine surface temperature record from 1850 to 2007. 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 0.740C.

• Past 50 years experiencing a rise of 0.13 C per decade.

Temperature reconstruction

Medieval warm period Little 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.

CO2 Versus Temperature

Before Present (BP) years . 1950 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 10700 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 ~7oC drop in temperature, in only 20 years.

• The event ended as suddenly as it had begun with a dramtic increase in temperature of ~7oC.

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.