In my last blog, I said that the only thing that heats Earth is the sun. That is not quite true. In the spirit of full disclosure, residual radioactivity in Earth’s core does supply some heat, mostly to hydrothermal vents and volcanoes. A lot of additional energy is provided by the hot air of politicians’ speeches. Still, “It’s the sun.”
Why, then, might Earth be warming? Is the energy we get from the sun changing? Is Earth doing something different with that energy? Answer: yes, to both.
Again, this isn’t rocket science or nuclear physics. But it does require that you pay attention and think a little bit.
Earth’s North Pole points toward a star we have cleverly named the North Star or the Pole Star. At some point, we may become more clever and name it the North Pole Star.
Earth’s axis is tilted (about 23.44 degrees at present) with respect to its orbital plane, so that part of the year the northern hemisphere is tilted toward the sun (summer) and part of the year the northern hemisphere is tilted away from the sun (winter). The southern hemisphere, not to be outdone, has the same seasons, but reversed.
Because the North Pole Star is so far away, it seems that the North Pole always points toward it. But while this is going on, Earth acts like a child’s gyroscope. In its travels about the sun, the place in the sky toward which the North Pole points rotates in a circle that takes about 26,000 years to complete. The North Pole Star will be a different star in not so many years. In fact, that’s happened several times in recorded history. This movement is (gyroscopic) precession.
In addition to precession, the axis of Earth “wobbles” in about an 18-year cycle (“nutation”) meaning that every 18 years or so the tilt toward the sun in summer is a tiny bit greater, and the tilt away from the sun in winter is a tiny bit less. Nine years afterwards, the tilt toward the sun in summer is a tiny bit less, and so on.
The orbit of Earth is an ellipse—a slightly squeezed circle. The amount of squeeze is measured as the eccentricity of the orbit. And that changes slightly in a 413,000 years-or-so cycle. Other aspects of the orbit with different periods combine to produce a cycle of about 100,000 years.
The combination of precession and orbital eccentricity then combine to create a roughly 21,000-year cycle. What this boils down to is that different hemispheres (northern, southern) get different amounts of light and heat from the sun and that amount changes in a 21,000 year cycle.
Because there is more land in the northern hemisphere than the southern, and because land absorbs sunlight better than water, today Earth absorbs more heat from the sun than it did about 10,500 years ago, and more than it will in 10,500 years.
In about 10,500 years, the “summer” and “winter” tilt will be reversed, and June and July will be winter months in the northern hemisphere, and December and January will be summer months. Australia may see a White Christmas—if we haven’t destroyed Earth before that.
Around 1920, an astronomer/geophysicist, Milutin Milanković merged these cycles mathematically and plotted them on graph paper. His hypothesis was that these cycles affected the amount of energy reaching and being absorbed by Earth, and therefore, affected global temperatures. A study of ice cores has validated this hypothesis, although there remain some questions that have yet to be answered. Milanković’s cycles are important, but are not the entire answer.
It’s still the sun, but it’s also sunspots.
We’ll look at those in the next post.
Gyroscopic precession: https://www.youtube.com/watch?v=ty9QSiVC2g0 [accessed 2016-11-18]
For an understandable explanation of Milanković cycles, and some excellent images, see https://en.wikipedia.org/wiki/Milankovitch_cycles
In something of an irony, in May 2016, Donald Trump, who has labeled climate change a "con job," a "hoax" and "bull ---t," applied to build a wall along a luxury golf course that he owns in Ireland that is threatened by rising seas caused by climate change.
The Republican Party Platform reads, in part, “Climate change… is the triumph of extremism over common sense… We support the development of all forms of energy… including coal, oil, natural gas, nuclear power, and hydroelectric… we support [fracking].” The platform’s support for renewable energy would be limited to private capital. Later, the platform reads, “The United Nations’ Intergovernmental Panel on Climate Change [IPCC} is a political mechanism, not an unbiased scientific institution… We reject the agendas of both the Kyoto Protocol and the Paris Agreement… We demand an immediate halt to U.S. funding for the U.N.’s Framework Convention on Climate Change…”
And we put these people in control of our government, to the ultimate detriment of the children, grandchildren, and great-grandchildren of my generation.
Earth’s climate achieved a balance shortly after the last ice age. How this happened is not rocket science. It’s basic chemistry, biology, and geology.
For eons, microscopic sea creatures busily absorbed Carbon Dioxide (CO2) from the ocean when creating their tiny shells of calcium carbonate (CaCO3), which settled to the ocean bottom, were compressed, and became limestone. Meanwhile, termites in tropical regions were busily creating CO2. Volcanoes were occasionally spewing CO2, Sulfur Dioxide (SO2), Hydrogen Sulfide (H2S) and particulates into the atmosphere. Subduction of tectonic plates (slowly, to be sure) was sliding limestone on the ocean floor under continental plates where some was eventually spewed back into the atmosphere from volcanoes as CO2. The orogenies that built mountains (also slowly) occasionally exposed limestone to erosion, returning some CO2 to the air. Trees absorb CO2 from the air, die, rot, and return that CO2 to the air, unless they are buried for millennia and turn into peat and coal.
There are many natural sources of CO2. There are many natural sinks for CO2 and Earth had achieved something of a balance before we (humankind) began burning, in a century-and-a-half, fossil fuels that had been laid down (thereby capturing carbon) for millennia.
We have measured the amount of CO2 in the air, and have seen it increase steadily. We have measured this directly on top of a mountain in Hawaii since about 1958. There has been a steady rise from less than 320 parts per million to over 400 parts per million.
We have measurements from Antarctic and Greenland ice cores of CO2 in the atmosphere going back to at least 425,000 B.C.E.
We know the CO2 that comes from burning fossil fuels (coal, oil, natural gas/methane) is demonstrably different from CO2 from current, natural sources. The simplest way to determine this is to look at the amount of Carbon 14 in the CO2. “Younger” CO2 has a large amount of Carbon 14. Carbon 14 has a half-life of 5,700 years, and does not exist in fossil fuels that are millions of years old… such as coal, laid down during the Carboniferous Period (c. 359—299 million years B.C.E.)
The correlation between rising atmospheric CO2 and rising temperatures has been measured and plotted since about 425,000 B.C.E. It’s a fact.
Earth is warming. That too, is a fact.
What is the source of the heat? The sun, only the sun, and nothing but the sun. And that will be the topic of the next post.
“Republican Party Platform 2016” downloaded 2016-08-07
http://www.nydailynews.com/news/politics/donald-trump-12-outrageous-moments-article-1.2714391 [Accessed 2016-11-16]
I have been a student of weather and climate ever since I became a private pilot and realized that my ability to predict weather was a life-and-death matter on cross-country flights. I have read and studied many references since before “global warming” and “climate change” became issues.
In case you missed it (and I found it on the BBC web site...not in any legitimate USA news source), the Noah's Ark "theme park" has opened in Kentucky (where else? Georgia, maybe?)
Perhaps the most poignant picture is of a child looking into a "cage" containing "dinosaurs."
See more at BBC News 7 July 2016 (www.bbc.com/news’world-us-canada-36767185
Ken Ham, leader of "Answers in Genesis," and creator of this travesty, believes and preaches that the universe was created by his god about 6,000 years ago, that dinosaurs lived at the same time as the earliest humans, and that all were destroyed in a world-wide flood...all except one family and representatives of all animals (including dinosaurs) that took refuge in the ark.
On the other hand, science has clearly demonstrated that the universe is more than 13 billion years old; that the earth is about 4.5 billion years ago; that life evolved from primitive replicating molecules; that dinosaurs became extinct about 65 million years ago; and that humans are the evolutionary descendants of small, burrowing mammals that survived the extinction event that killed the dinosaurs.
Even though the ark theme park promotes scientific illiteracy and a specific religious view, it was given a tax incentive by the state of Kentucky valued at $18 million dollars, in what is a clear violation of the separation of church and state.
Photo credit: BBC and AP
Registered Curmudgeon, scientist, skeptic, humanist, and writer.