Do you know what one significant difference is between Uranus and all the other planets in the solar system? Unlike the other seven planets, which, more or less, rotate in a "normal" up-down position (or down-up in the case of Venus), Uranus is quite abnormal. Its north-south pole rotational axis lies almost in the ecliptic because it is tilted by 97.8 degrees and rotates in an 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 its 84-year-long orbit, while if you are settled near the equator, thanks to the 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 that happened in the early solar system), the weather and climate on Uranus are always dramatic in the form of huge apocalyptic storms one after another.
Of course, we don't have to go that far outside the Sun's habitable zone to prove that the position of the rotational axis can cause dramatic climate changes on the planet's surface. Let's look in our own front yard and see how a couple of main astronomical properties influence the climate on Earth. Is it possible that even a slight change 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 a 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 the scientific mainstream at the time, but this didn't stop Milankovitch from expanding his idea and eventually creating a mathematical model capable of calculating the time frames of all climate changes that happened in the past half a million years and further. Today this theory is well known as Milankovitch Cycles or Insolation Theory, with approximately 100,000 years of 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 the Foresight Institute recovered from a Greenland ice core also show a drop in temperature for the past 50,000 years similar to the Milankovitch graph shown below. The last curve in the graph represents stages of glaciation, or, in simple words, turning the Earth into a giant ice ball in the past million years. The peaks (hot and cold) are called interglacial and glacial periods. Right now we are living in the fourth interglacial period in the 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 frames, let's first try to understand the first three curves.
The basics under the theory are so-called insolation calculations based on orbital cycles (cycled amount of sunlight hitting the Earth). Milankovitch used Ludwig Pilgrim's orbital calculations to make a detailed model of insolation periods initially for the previous 130,000 years (later expanded to 650,000 years). Three orbital variations are used in this complex math. The first one is changes in Earth's orbit around the sun (eccentricity), the second is the tilt of Earth's axis (obliquity), and the third represents the wobble of Earth's axis (precession).
The Eccentricity Cycle (Elliptical Cycle)
Due to other planets' gravitational influences, Earth's orbit has an approximate 100,000-year cycle of slight changes. It goes from a nearly circular orbit toward a mildly elliptical one. During the "elliptical" period, Earth is receiving less solar radiation compared to the "circular" part.
The Obliquity Cycle (Axial Tilt)
We saw in the beginning how Uranus' unusual axial tilt can cause dramatic climate. With the 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 a planet's hemispheres can be tilted toward or against the Sun, giving the planet seasons with different amounts of sunshine during one orbit cycle. The lower angle means that sun rays are penetrating the atmosphere better, warming the surface more compared to the planet's other hemisphere, where the angle is higher. Now if we add the fact that the axis angle is changing over time, and in Earth's case this goes from 22.1° to 24.5° and back again over a period of 41,000 years, it is obvious that when this axial tilt changes over time by as little as 1 degree, it can cause serious effects 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 is that axis changing its angle over time, but it also, like some spin-top toy, wobbles. This "feature" is positioning Earth's axis today almost directly toward Polaris, commonly known as the "North Star", and in half a period of time it will be pointing directly to Vega. This is caused by the planet not being a perfect round ball and also by the 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.
Ok, now that we know how Earth "works" in relation to its own climate, I think it is the perfect time in this post to ask the obvious question(s). As we know for sure that we have been living for some time now in the peak of an interglacial period, is it possible to use the theory and glacial data to predict the next ice age? More importantly, are humans capable enough to postpone the next ice age with emissions of carbon dioxide and other greenhouse gases? In the Nature Geoscience paper named "Determining the natural length of the current interglacial" they concluded that, according to all we know about insolation and CO2 forcing, the next ice age is very close, and it should start happening within the 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 an even more obvious question. Did we cross the point of no return? Did we manage to cheat natural astronomical cycles and actually head toward global warming instead of an ice age? Or the oceans will prevail one more time and over the next millenniums will manage to absorb a record amount of carbon dioxide in the previous million years and introduce the next ice age with little delay this time? Again, some facts are pointing toward two cruel possible scenarios. If the next ice age eventually comes, it will ultimately pose a significant threat to mankind in the form of a lack of energy, food, and enough landmasses to sustain a large 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 raise ocean levels and sink large coastal cities all over the world. About 10% of people live in low-elevation coastal zones. Just imagine the migration of 600 million people in the potential scenario of global warming.
This is the lottery we cannot win. It seems that time is running out, and within the next decade, we need to find a 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 a simple matter of pure survival.
No pressure.
Original post date: June 2013, Updates: November 2016, December 2017
Image ref:
https://www.beforetheflood.com/
https://sites.google.com/a/isd47.org/rogersesci2015third/home/20-the-weirdest-tilt
http://www.imdb.com/title/tt3230854/
Story refs:
http://en.wikipedia.org/wiki/Milankovitch_cycles
http://www.imdb.com/title/tt0436992/
More references:
http://www.universetoday.com/19305/seasons-on-uranus/
http://en.wikipedia.org/wiki/Ice_age
http://www.bbc.co.uk/news/science-environment-16439807
http://co2now.org/
http://ossfoundation.us/projects/environment/global-warming/milankovitch-cycles
http://muller.lbl.gov/pages/IceAgeBook/IceAgeTheories.html
http://www.eoearth.org/view/article/154612/
http://frank-davis.livejournal.com/39586.html
Uranus—a hypothetical view from the nearest moon
Of course, we don't have to go that far outside the Sun's habitable zone to prove that the position of the rotational axis can cause dramatic climate changes on the planet's surface. Let's look in our own front yard and see how a couple of main astronomical properties influence the climate on Earth. Is it possible that even a slight change 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 a 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 the scientific mainstream at the time, but this didn't stop Milankovitch from expanding his idea and eventually creating a mathematical model capable of calculating the time frames of all climate changes that happened in the past half a million years and further. Today this theory is well known as Milankovitch Cycles or Insolation Theory, with approximately 100,000 years of 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 the Foresight Institute recovered from a Greenland ice core also show a drop in temperature for the past 50,000 years similar to the Milankovitch graph shown below. The last curve in the graph represents stages of glaciation, or, in simple words, turning the Earth into a giant ice ball in the past million years. The peaks (hot and cold) are called interglacial and glacial periods. Right now we are living in the fourth interglacial period in the 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 frames, let's first try to understand the first three curves.
The basics under the theory are so-called insolation calculations based on orbital cycles (cycled amount of sunlight hitting the Earth). Milankovitch used Ludwig Pilgrim's orbital calculations to make a detailed model of insolation periods initially for the previous 130,000 years (later expanded to 650,000 years). Three orbital variations are used in this complex math. The first one is changes in Earth's orbit around the sun (eccentricity), the second is the tilt of Earth's axis (obliquity), and the third represents the wobble of Earth's axis (precession).
The Eccentricity Cycle (Elliptical Cycle)
Due to other planets' gravitational influences, Earth's orbit has an approximate 100,000-year cycle of slight changes. It goes from a nearly circular orbit toward a mildly elliptical one. During the "elliptical" period, Earth is receiving less solar radiation compared to the "circular" part.
The Obliquity Cycle (Axial Tilt)
We saw in the beginning how Uranus' unusual axial tilt can cause dramatic climate. With the 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 a planet's hemispheres can be tilted toward or against the Sun, giving the planet seasons with different amounts of sunshine during one orbit cycle. The lower angle means that sun rays are penetrating the atmosphere better, warming the surface more compared to the planet's other hemisphere, where the angle is higher. Now if we add the fact that the axis angle is changing over time, and in Earth's case this goes from 22.1° to 24.5° and back again over a period of 41,000 years, it is obvious that when this axial tilt changes over time by as little as 1 degree, it can cause serious effects 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 is that axis changing its angle over time, but it also, like some spin-top toy, wobbles. This "feature" is positioning Earth's axis today almost directly toward Polaris, commonly known as the "North Star", and in half a period of time it will be pointing directly to Vega. This is caused by the planet not being a perfect round ball and also by the 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 the real world, we humans are too small in both size and time frame of our individual existence; otherwise, I am not sure what the exact consequence would be if we could really sense planetary motions. Sci-fi aside, all these three motion cycles can cause changes in the quantity of sunlight hitting the Earth's surface, and insolation theory in a nutshell is basically one mathematical model capable of calculating solar forcing (yellow line in the above graph) for any chosen latitude at any point in time, considering the orbital position of the Earth and the condition of the 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 the 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 do not correlate perfectly with insolation theory. There are more suggestions, like including the longest eccentricity cycle or 400,000 years of carbon dioxide variations in oceans and even including consequences of "artificial" production of greenhouse gases since the early 19th century and the birth of the 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 the most complex sciences out there. There are simply too many inputs and variables. One historical data point I read in Wikipedia was that Milankovitch needed 100+ days to manually calculate cycles for the 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 the perfect time in this post to ask the obvious question(s). As we know for sure that we have been living for some time now in the peak of an interglacial period, is it possible to use the theory and glacial data to predict the next ice age? More importantly, are humans capable enough to postpone the next ice age with emissions of carbon dioxide and other greenhouse gases? In the Nature Geoscience paper named "Determining the natural length of the current interglacial" they concluded that, according to all we know about insolation and CO2 forcing, the next ice age is very close, and it should start happening within the 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 an even more obvious question. Did we cross the point of no return? Did we manage to cheat natural astronomical cycles and actually head toward global warming instead of an ice age? Or the oceans will prevail one more time and over the next millenniums will manage to absorb a record amount of carbon dioxide in the previous million years and introduce the next ice age with little delay this time? Again, some facts are pointing toward two cruel possible scenarios. If the next ice age eventually comes, it will ultimately pose a significant threat to mankind in the form of a lack of energy, food, and enough landmasses to sustain a large 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 raise ocean levels and sink large coastal cities all over the world. About 10% of people live in low-elevation coastal zones. Just imagine the migration of 600 million 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 the next decade, we need to find a 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 a simple matter of pure survival.
No pressure.
Original post date: June 2013, Updates: November 2016, December 2017
Image ref:
https://www.beforetheflood.com/
https://sites.google.com/a/isd47.org/rogersesci2015third/home/20-the-weirdest-tilt
http://www.imdb.com/title/tt3230854/
Story refs:
http://en.wikipedia.org/wiki/Milankovitch_cycles
http://www.imdb.com/title/tt0436992/
More references:
http://www.universetoday.com/19305/seasons-on-uranus/
http://en.wikipedia.org/wiki/Ice_age
http://www.bbc.co.uk/news/science-environment-16439807
http://co2now.org/
http://ossfoundation.us/projects/environment/global-warming/milankovitch-cycles
http://muller.lbl.gov/pages/IceAgeBook/IceAgeTheories.html
http://www.eoearth.org/view/article/154612/
http://frank-davis.livejournal.com/39586.html
http://wiki.answers.com/Q/What_axis_tilts_do_the_planets
https://en.wikipedia.org/wiki/Axial_tilt
http://www.technologyreview.com/article/416786/global-warming-vs
https://en.wikipedia.org/wiki/Axial_tilt
http://www.technologyreview.com/article/416786/global-warming-vs