CLIMATE CHANGE and the MILANKOVITCH CYCLES

Many people outright deny the global climate is changing or that humans could possibly influence the climate.  They further argue that whatever changes are taking place are due to natural cycles although they never explain what those are.  Well, here is the explanation.

Climate change is a long term event that occurs in three predictable cycles as the earth orbits around the sun: Tilt (41k years), precession (19k to 24k years), and eccentricity (100k to 413k years).  They are known as the Milankovitch Cycles after the Serbian astronomer and mathematician who first calculated their magnitude in the 1920's.  The cycles change the climate by altering the amount of solar radiation that reaches the earth.

The tilt of the earth accounts for the changing seasons: winter, spring, summer and fall. The reason is the axis of the earth is at a different angle than the axis of the sun. Consequently, as the earth orbits around the sun the North Pole is inclined away from the sun in the winter and toward the sun in the summer. The South Pole is just the opposite.

The four seasons.

However, the tilt is not fixed and it cycles between 21.5 to 24.5 degrees over a span of 41,000 years. When the tilt is greatest, at 24.5 degrees, whichever pole is facing the sun will be warmer than usual in the summer and the opposite pole will be colder at the same time. This fluctuation causes the polar ice caps to expand and shrink accordingly.

The second cycle is precession which takes 21,000 years. It is a wobble to the tilt of the earth like the motion of the gyroscope below. The wobble increases the tilt and also effects the temperature of the earth and consequently the size of the polar ice caps. 

Precession

The last cycle is eccentricity which is an oscillation in the shape of the orbit of the earth around the sun.  Sometimes the earths orbit is near circular but over a period of 100,000 years the orbit flattens and lengthens.  Since the sun is not in the center of that orbit the planet is further away from the sun more of the time.  In the example given below the position of the sun is greatly exaggerated but it illustrates the idea.

Eccentricity

When the eccentricity is at its greatest the earth is closer to the sun during perihelion (91.4 million miles) and 3.1 million miles further away when at aphelion (94.5 million miles).   

Not to scale.

Individually and collectively the Milankovitch cycles are responsible for fluctuations in the amount of solar radiation that reaches the earth. Of the three cycles eccentricity has the greatest effect on the climate and is the cause of many global warming and cooling events in the past. A study of ocean sediments indicate ice ages have occurred approximately every 100,000 years for the last five million years. Currently the earth is moving toward aphelion and should be cooling off but it is not.

Global Warming is short term and refers to the human caused rise in the global temperature from greenhouses gases, primarily carbon dioxide. When fossil fuels such as coal or oil are burned carbon dioxide is released into the atmosphere. Like a greenhouse it traps heat from solar radiation and also heat from volcanism, forest fires, human industry and cities.  Since the industrial revolution started in 1763 the climate has been warming sporadically since 1880 and continually since 1980.

Global warming is not something contrived in just the last thirty years. In 1886 Savante Arrhenius, a Swedish physicist and chemist, was the first person to calculate human-induced global warming by carbon dioxide. He received the Nobel Price for chemistry in 1903. 

Guy Stewart Callendar, a British steam engineer and amateur climate scientist published a theory in 1938 that linked rising carbon dioxide concentrations in the atmosphere to global temperature. He thought it would be beneficial in delaying the return of the ice age. He was correct.

In the 1950's Callendar's claims provoked a few scientists to look at his work using better instruments and newer technologies that confirmed his conclusions. Their work was financed by the United States Military to determine if it could be useful in a war with Russia.

Al Gore, a member of the United States House of Representatives, held the first congressional hearings on climate change in 1976. In 2006 he presented and narrated the documentary film, "An Inconvenient Truth", which stirred global awareness but little response.

In 1988 NASA scientist James Hansen presented hard data to Congress that global warming was happening. Shortly afterward climatologists began informing the general public of the problem and its dangers, few people paid attention.  

To date 185 member countries of the United Nations have ratified the Paris Climate Agreement, a treaty to address global warming and to reduce emissions of greenhouse gases. Russia, the United States and ten other countries have not agreed to the treaty.

Climate change is a planetary cycle that normally takes place over one-hundred thousand years that would allow time for humans to adapt. Global warming is a symptom of climate change that shouldn't currently be happening that will create unnecessary human suffering and staggering economic cost in just a few hundred years.

An analogy from the National Aeronautical and Space Administration:  If  climate change was the flu,  global warming is its fever. 

Mark Thomas