Chapter 19.1-19.3Causes of Climate Change Part I:

Milankovitch Cycles

Climate Cycles =400

Milankovitch Cycles

• Milankovitch Cycles vary the amount of sunlight parts of the Earth receive at certain times of year

• Cycles can increase or decrease seasonal ______________• Eccentricity, Obliquity, Precession are the three changes

in the Earth’s movement analyzed in the Milankovitch cycles

Milankovitch Cycles are created by changes in the geometry of Earth’s orbit around the sun and changes in Earth’s tilt.

Geometry of the Earth & Sun• _______ is more quickly

affected by changes in heating than water.

• Also, Oceans circulate, which will lessen seasonal variatiions.

• Since most continents are in the Northern Hemisphere, Milankovitch Cycles have a greater effect on seasons in the Northern Hemisphere, and these effects are what can cause global glacial and interglacial periods.

• In general, ______ extreme seasonal changes lead to glacial periods, ______ extreme changes lead to interglacial periods. Why? More extreme summers = more melting of snowpackMore extreme winters = less snow (too cold for water vapor)

Eccentricity• Eccentricity: the change in the shape of the Earth’s

________, ranging from nearly circular to more elliptical on a 100,000 year cycle.

• Greater eccentricity increases the difference between aphelion (furthest point from the sun) and the periphelion (closest point to the sun).

• Whether a greater eccentricity will cause greater seasonal differences depends on the combination of eccentricity with _______________(orientation of Earth’s tilt relative to the sun).

• We are currently in a period of _______ eccentricity.

More Extreme

Less ExtremeCurrent:

Obliquity (or Axial Tilt)• Obliquity: degree of the tilt of the Earth’s axis. • Variation in tilt ranges from 21.5 and 24.5 in a

cycle of 41,000 years.• Current tilt is ______ and is _______________• Less tilt results in ________ seasonal differences,

which can lead to ________________ glaciation

More Extreme Less Extreme

Current

Precession (or Wobble)• Precession: Change in the orientation of the Earth’s

axis relative to its ________. (Wobble of axis.) • Cycle is 23,000 years.• Currently the periphelon (closest point to sun) occurs

during Northern Hemisphere’s __________, causing ______ extreme seasons in the Northern hemisphere.

• When axis parallel to sun (equinoxes) during aphelion and periphelon, hemispheres have similar contrast in seasons.

More Extreme in North

Less Extremein North

Current:

Milankovitch Cycles

At times when Northern Hemisphere summers are _________(farthest from the Sun due to precession and greatest orbital eccentricity) and winters are ___________ (minimum tilt), snow can accumulate on and cover broad areas of northern America and Europe. At present, only precession is in the glacial mode, with tilt and eccentricity not favorable to glaciation.

• Even when all the orbital parameters favor glaciation, the increase in winter snowfall and decrease in summer melt would barely be enough to trigger glaciation, not to grow large ice sheets.

• Ice sheet growth requires the support of ________________ feedback loops. The largest one is probably tied to ocean uptake of carbon.

Climate Cycles

Natural Climate Cycles• End of last ice age

about 10,000 yr BP

• Now in warm interglacial period

• Based on ice core data, analysis of trapped gas (CO2 is measured directly; O2 isotopes give temp. information)

• Correlation between CO2 & mean temp.

=400

Natural Climate Cycles• CO2 and Temperature correspond very closely• What has caused past CO2 variations? (ocean

biological activity, ocean circulation patterns?)Current CO2

(~399 ppm)Past CO2 max (~300ppm)

More GreenhouseEffect

Less CO2

Removed fromAtmosphere

Less Productivity (photosynthesis)

In Oceans

Warmer Oceans

Warmer Global Temperatures

Why have global temperature and CO2 variations correlated so closely with each other in the pre-industrial past?

--Positive feedback loop between temperature and ocean productivity (photosynthesis) may be key