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Natural Drivers of Climate Change

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Let’s Explore What is Driving These climate Cycles over the last 800,000 years

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Orbital Scale Forcings

Eccentricity

(shape of Earth’s orbit)

Obliquity

(tilt of axis of retention)

Precession

(wobble of axis of rotation)

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Time Scale is important here!

Eccentricity (shape) – 100,000 year cycle

Obliquity (tilt) – 40,000 year cycle

Precession (wobble) – 23,000 year cycle

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Eccentricity

Variations in the shape of Earth’s orbit varies (100,000 year cycle)

Low eccentricity (0.005)

(more circular orbit)

High eccentricity (0.060

(more elliptical orbit)

The Earth’s actual orbit is not circular but slightly elliptical. The noncircular shape of the earth’s orbit is the result of the gravitational pull of other planets on the earth as it moves through space.

Variations in the shape (eccentricity) of Earth’s orbit varies (100,000 year cycle)

Elliptical - Circular

Low eccentricity - round orbit (0.005)

High eccentricity – eliptical orbit 0.0607

Today = 0.016

Dimensionless # ratio of long to short axis. E = square root a²-b²/a, Shorter axis never more than 3.5%shorter than the longer axis

Does not affect seasonal contrast

Changes total solar flux by 0.2%

If circular same, if max 0.06, currently 0.016

At it farthest point from the sun earth is 1.67% farther from the sun as compared to a circular orbit

The Earth's eccentricity varies primarily due to interactions with the gravitational fields of Jupiter and Saturn.

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Tilt of Earth’s rotational axis (40,000 year cycle)

Varies 21.39-24.5°

Today 23.5°

What climate or weather related phenomenon would this affect?

Obliquity

The Earth rotates on it axis that passes through the poles . This axis is tilted 23.5°. The hemisphere that points towards the sun receives more direct solar heating and is warmer than the hemisphere that points away form the sun.

This tilt explains the seasons and why the northern hemisphere seasons are the opposite as the southern hemisphere seasons.

Summer heating is greater and winter cooling is greater when the tilt angle is high. Summers are cooler, therefore, when the tilt angle is low. Persistence of year round snow is favored by coDoes not affect low lats. -Obliquity changes have little effect on radiation reception at the equator, but increases towards high latitudes.

Therefore has a major influence on glacial/interglacial cycles.

Amplifies or supresses seasonal diff’s

https://www.flickr.com/photos/saschapohflepp/3277171190/sizes/z/

On side: 41,000 year cycle, Smaller tilt –less seasonal contrast, milder conditions (glaciation)

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Precession� �- Wobble of Earth’s rotational axis�- Angle of tilt not changed but direction of tilt changes�

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Precession�Determines in which season the Earth is nearest to the sun. �

Less distance

Warmer Summer

Earth-Sun Distance in June

More distance

Cooler Summer

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Phases

Milankovitch values small

subtle differences

but when cycles in phase,

effect greatly magnified

when cycles out of phase

½ effect reduced

Two waves out of phase

Two waves slightly out of phase

Two waves in phase

Likely glaciation:

- eliptical orbit

- low tilt

- high Earth-sun distance in June

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Which part of the Milankovitch cycle

do you see in this record?

See handout

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Eccentricity

Precession

Obliquity

Which orbital parameter seems to affect temperature the most?

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How much does solar variability (irradiance) affect temperature?

Do these wiggles match?� �

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Eccentricity - elliptical orbit means less solar heating

Today - low eccentricity (0.016)

Decreasing to 0 30,000 years from now

Elliptical orbit

Slightly cooler

Circular orbit

Slightly warmer

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Obliquity

Low tilt angle means cool summer, mild winters favor year round snow (glacials)

Warmer Summer

Maximum tilt

Colder Summer

Minimum tilt

Tilt Angle