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Ice Age vs Global Warming

Do you know what is one significant difference between Uranus and all other planets in Solar system? Unlike the other seven planets who, more or less, rotate in "normal" up-down position (or down-up in case of Venus), Uranus is quite abnormal. It's north-south pole rotational axis lies almost in ecliptic because it is tilted by 97.8 degrees and rotates in almost vertical direction toward the orbiting plane. In simple words, Uranus is one giant rolling ball where if you are located on its pole, you would be experiencing only one day and one night during 84 years long orbit while if you are settled near the equator, thanks to ultra-fast rotation time (for a giant planet) of 17 hours you would be experiencing fast switching between day and night and during both solstices the Sun would always be on the horizon. Thanks to this strange position of Uranus axis (probably due to some cosmic collision happened in early Solar system), the weather and climate on Uranus are always dramatic in form of huge apocalyptic storms one after another.

Uranus - a hypothetical view from the nearest moon

Of course, we don't have to go that far outside Sun's habitable zone to prove that position of rotational axis can cause dramatic climate changes on the planet's surface. Let's look in our own front yard and see how couple of main astronomical properties influence the climate on Earth. Is it possible that even a slight changes in, for example, Earth's orbit can cause some dramatic climate changes over the years? I am sure this question was exactly what was itching Milutin Milankovitch's mind almost century ago when he first read James Croll's bold idea of the effects of variations of the Earth's orbit on climate cycles. Croll's theory was generally rejected by scientific mainstream at the time but this didn't stop Milankovitch to expand his idea and eventually create mathematical model capable of calculating time frames of all climate changes happened in past half a million years and further. Today this theory is well known as Milankovitch Cycles or Insolation theory with approximately 100.000 years cyclicity between ice ages.

Unfortunately, Milankovitch died some 20 years before his model was proven in 1976 when one geological study confirmed consistency of the calculated data with the examined deep-sea sediment cores. Past records of temperature measurement provided by Foresight Institute recovered from a Greenland ice core also shows drop in temperature for past 50.000 years similar to the Milankovitch's graph shown below. The last curve in the graph represents stages of glaciation or in simple words turning the Earth into giant ice ball in past million years. The peaks (hot and cold) are called interglacial and glacial periods. Right now we are living in fourth interglacial period in past 400.000 years and soon, astronomically speaking, we are going to start heading back toward another ice age. Exactly when it is going to happen is hard to predict but before speculating about future time frame lets first try to understand first three curves.

The basics under the theory is so called insolation calculations based on orbital cycles (cycled amount of sunlight hitting the Earth). Milankovitch used Ludwig Pilgrim's orbital calculations to make detailed model of insolation periods initially for previous 130.000 years (later expanded to 650.000 years). Three orbital variation are used in this complex math, first one is changes of Earth's orbit around the sun (eccentricity), second is the tilt of Earth's axis (obliquity) and third represents the wobble of Earth's axis (precession).

The Eccentricity Cycle (Elliptical Cycle)
Due to other planet's gravitational influences, Earth orbit has approximate of 100.000 years cycle of slight changes. It goes from nearly circular orbit toward mildly elliptical. During "elliptical" period Earth is receiving less solar radiation comparing to the "circular" part.

The Obliquity Cycle (Axial Tilt)
We saw in the beginning how Uranus unusual axial tilt can cause dramatic climate. With exception of Mercury and Venus with their almost vertical no-tilt position of rotational axis (if we disregard Venus's almost 180° tilt positioning the planet upside down), all other planets are tilted around 25 degrees. This means that planet's hemispheres can be tilted toward or against the Sun giving the planet seasons with different amount of sunshine during one orbit cycle. The lower angle means that sun rays are penetrating the atmosphere better warming the surface more comparing to the planet's other hemisphere where the angle is higher. Now if we add the fact that axis angle is changing over time and in Earth's case this goes from 22.1° to 24.5° and back again over period of 41.000 years it is obvious that when this axial tilt changes over time as little as 1 degree, it can cause serious effect to the global insolation mentioned above.

The Precession Cycle (Wobble)
The last, but not the least motion in this equation is Earth's wobbling. Not only that axis is changing its angle over time, it also, like some spin-top toy, wobbles. This "feature" is positioning Earth's axis today almost directly toward Polaris, commonly known as "North Star" and in half period time it will be pointing directly to Vega. This is caused by planet not being perfect round ball and also by close vicinity of the Sun and the Moon with their strong gravitational forces. This cycle is the shortest and it occurs every 26.000 years.

Doctor Who in one of the episodes said that he was capable of feeling all these motions as they happen but hopefully and thankfully, in real world, we humans, are too small in both, size and time frame of our individual existence, otherwise I am not sure what exact consequence would be if we could really sense planetary motions. SciFi aside, all these three motion cycles can cause changes of sunlight quantity hitting the Earth's surface and insolation theory in its nutshell basically is one mathematical model capable of calculating solar forcing (yellow line in above graph) for any chosen latitude at any point of time considering orbital position of Earth and condition of planetary axis. Of course, even though this theory has overwhelming support in mainstream science it's still far from being perfect. There are problems and concerns posted in previous years and decades and the main one is that it doesn't include inclination of the earth's orbit to the ecliptic which is another 100,000 year cycle, more or less. Also in observed glacial data even though the 100ky cycle is recognized, the temperature records not correlate perfectly with insolation theory. There are more suggestions, like including the longest eccentricity cycle or 400.000 years carbon dioxide variations in oceans and even including consequences of "artificial" producing of greenhouse gases since early 19th century and birth of industrial revolution. In other words the theory has plenty of room for improvement and its perfection is expected.

One thing is for sure, this research is one of those most complex science out there. There are simply too many inputs and variables. One historical data I read in Wikipedia was that Milankovitch needed 100+ days to manually calculate cycles for past 650.000 years and only for three latitudes.

Leonardo DiCaprio's Before the flood

Ok, now that we know how Earth "works" in relation to its own climate, I think it is perfect time in this post to ask the obvious question(s). As we know for sure that we are living for some time now in the peak of interglacial period, is it possible to use the theory and glacial data to predict next ice age? More importantly are humans capable enough to postpone next ice age with emissions of carbon dioxide and other greenhouse gases? In the Nature Geoscience's paper named "Determining the natural length of the current interglacial" they concluded that according to all we know about insolation and CO2 forcing next ice age is very much close and it should start happening within next 1500 years. The only condition is for atmospheric CO2 concentrations to be lower than 240±5 ppmv.

Guess what? On this very day it is 400 ppmv (May, 2013).

Well, now is the time for even more obvious question. Did we cross the point of no return? Did we manage to cheat natural astronomical cycles and actually heading toward global warming instead of ice age? Or the oceans will prevail one more time and over next millenniums will manage to absorb record amount of carbon-dioxide in previous million of years and introduce the next ice age with little delay this time? Again some facts are pointing toward two cruel possible scenarios. If next ice age eventually come, it will ultimately pose significant threat for mankind in form of lack of energy, food and enough land masses to sustain large number of human population, not to mention all other species. On the other hand if CO2 levels uncontrollably continue to rise the resulting global warming is equally or even more dangerous. Melted ice will rise ocean levels and sink large coastal cities all over the world. About 10% of people live in low-elevation coastal zone. Just imagine migration of 600 millions people in the potential scenario of global warming.

The Expanse - Flood blockage in futuristic NYC

This is the lottery we cannot win. It seems that time is running out and within next decades we need to find solution for ultimate control of greenhouse gases. Additionally with all potential hazards on the way it seems that we can't allow nature to take us in some dramatic ice age or global warming.

It's simple matter of pure survival.

No pressure.

Original post date: June 2013, Updates: November 2016, December 2017

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