apsidal precession, axial precession, Earth Science, Earth's orbit, eccentricity, Global warming, Ice Age, insolation, Milankovitch Cycles, Milution Milankovic, obliquity, Warm Age
PART III – Should We Be In An Ice Age Now?
RECAP: In Part I of this series, we looked at how scientists have determined that Earth has experienced regular cycles of cold climates followed by brief periods of warm climates during the last 400,000 years. We learned that the current cycle has been different because the warm period has persisted when past warm climates have rapidly dropped back into a cold climate. We also discussed how the Sun acts as a ‘battery charger’ for Earth’s climate.
Part II of the series explained that Earth’s orbital relationship with the Sun also follows a cyclic pattern and that almost 100 years ago, a Serbian named Milutin Milanković proposed possible mechanisms related to Earth’s tilt and orbit that could be the root cause of the regular cycle of Ice Ages.
PART III – Should We Be In An Ice Age Now?
No one can say for certain whether or not that we should be in an Ice Age today. Past Warm Ages have typically collapsed back into a cooler period within a few thousand years followed by a complete return to an Ice Age within about 10,000 years. If Earth past climate history is correct then our planet should be in a cooling period, if not into a full-scale Ice Age. Instead, Earth is warming. The Milankovitch Cycles don’t all concur on this issue, but there is some intriguing evidence that suggests we have missed a cooling period based on Earth’s orbit and tilt.
Consider the factors discussed in Part II of this series.
Orbit Eccentricity or Circular to Ellipse
Our orbit eccentricity is about one-third the way from our lowest level, meaning Earth’s orbit is becoming more circular. It’s cycle is about the same as Earth’s climate cycle, so it could be a significant factor. Interestingly, the eccentric peak of .02 during the current cycle was half to one-third of the peak past three cycles (.04 to .06.)¹ Could that be a factor in the prolonged warm period? Possibly, but why? Earth just passed the peak a few thousand years ago so, does a low peak eccentricity result in a prolonged Warm Age?
Obliquity or Earth’s Tilt On Its Axis
Earth is about halfway between our high and low peak tilt angles. Our planet’s tilt, or obliquity is on an approximate 41,000 year cycle, so we were just passing through our highest peak obliquity at the start of this Warm Period. If high tilt angle is a trigger for a Warm Age, then we should be cooling down, unless obliquity must be coupled with another factor to trigger a cooling period.
Axial Precession or Earth’s Wobble
Earth’s axis wobbles and it takes 26, 000 years to complete one cycle. It is hard to see a connection with the slow regression of the seasons and Earth’s climate, but perhaps the cycle of axial precession couples with another factor to trigger a cooling period, or sustain a Warm Age.
Apsidal Precession or The Hulu Hoop Effect
Apsidal precession is factor has some interesting possibilities on how it might impact Earth’s climate. Currently the Summer in the northern hemisphere occurs when Earth is farthest from the Sun (aphelion.) Our closest approach to the Sun (perihelion) occurs during Summer in the southern hemisphere.
Earth’s northern hemisphere is about 40% land and 60% water. The southern hemisphere is about 20% land and 80% water. Land that is not covered with ice absorbs more energy than water because water reflects more of Sun’s energy back into space. In Part II we learned that the hemisphere that is in summer during perihelion receives 23% more solar radiation. Because of the greater land mass, the northern hemisphere will retain more of the summer Sun’s energy in 10,000 years (when perihelion occurs in July) than the southern hemisphere does currently.
From a standpoint of apsidal precession, Earth should be in the coldest period since we are closest to the Sun when the smallest percentage of our land mass will absorb the energy or insolation.
The tilt of Earth’s orbital plane off of the invariable plane is on a 100,000 year cycle, which coincides with Earth’s climate cycle. Since higher angles of our orbital plane result in a higher obliquity and magnify the effect of land mass absorption differential between the two hemispheres, it could be a factor in triggering the Ice/Warm Age cycles; however, it is unclear how this factor could contribute to the prolonged warm period.
Are We Missing an Ice Age?
Earth’s climate cycle does not follow a perfect 100,000 year pattern. Most people would be happy if we never went into another Ice Age; however, if we have missed the trigger of the next Ice Age, what does that mean for our climate? Will Earth’s delicate climate balance be ruined leading into a runaway warm period or will the next Ice Age come in a rapid onset like in a disaster movie?
The Sun charges Earth’s climate ‘battery’ and variations in how much solar radiation our planet absorbs dramatically affects the environment for all life. It will be important for scientists to discover what is happening to our climate and why. Life on Earth exists in a narrow band that is not to cold and not to hot and we have no practical methods to reinforce or siphon off the Sun’s energy in a crisis.
While scientists to continue to examine this issue there are other issues that should be considered beyond climate. At least for the past 400,000 years, the Warm Ages have been relatively brief periods. It is during those brief periods of warmth that life has flourished, then the Earth has been cleansed with the next Ice Age. What will happen as insects, reptiles, and bacteria continue to evolve and expand without an Ice Age to push back their spread across the globe? Is it possible that too much life will threaten human existence?
These are all questions that have to be answered as long as the Earth continues to avoid the next Ice Age.
PART I – Should We Be In An Ice Age Now?
PART II – Understanding the Milankovitch Cycles, Clues to Earth’s Climate Changes
NOTES AND REFERENCES
¹Wikipedia – The Free Encyclopedia. (2011). Milankovitch Cycles. Retrieved November 13, 2011, from http://en.wikipedia.org/wiki/Milankovitch_cycles.
IMAGE 1.0 – Image thanks to http://www.space4case.com/mmw/pages/space4case/solar-system/earth/artic.php
IMAGE 1.1 – Image thanks to Wikimedia Commons at http://en.wikipedia.org/wiki/File:Precession_and_seasons.jpg
IMAGE 1.2 – Image thanks to http://www.learner.org/jnorth/tm/humm/WhyComeGlobalGame.html
IMAGE 1.3 – Image thanks to http://www.learner.org/jnorth/tm/humm/WhyComeGlobalGame.html
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