The Milankovitch Cycle: The Difference Between Natural and Anthropogenic Heating (Credit: BBC)

   ​Sometimes it can be unclear how natural and anthropogenic heating of the Earth are different. Throughout Earth’s history, it has gone through phases of frigid temperatures (ice ages) and hot temperatures (interglacial periods). The process responsible for this natural climate change is called the Milankovitch Cycle, named after the Serbian astronomer who calculated the three major factors in the cycle that change the climate. These three factors are:
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1. Eccentricity
2. Axial Tilt
3. Earth’s “Wobble”

   
   These three factors all deal with the positioning of the Earth relative to the Sun. The first factor is eccentricity, or the shape of Earth’s orbit around the Sun. Over time, Earth’s orbit will become more or less elliptical on a 100,000-year cycle, changing how close it gets to the Sun as it orbits. You can imagine this by taking a circular orbit and flattening it to make an oval-like orbit. After a while, the now-squashed circle will return to its original form. You can see that, as the shape gets more oval-like, the Earth will get closer and farther away from the Sun as it orbits, much more than when the shape is more circular. Right now, we have a more circular orbit around the Sun.

   Next, is the axial tilt of the Earth. This is just as the name implies: the change of tilt of Earth’s axis. Earth’s axis changes from an angle of 21.5 degrees to 24.5 degrees over 41,000 years, which in turn changes how much solar radiation the polar regions receive. The steeper the angle of the Earth’s tilt, the more solar radiation the polar region that faces the Sun receives, and the less solar radiation the opposite polar region receives.

   The third and final factor that influences climate in the Milankovitch Cycle is Earth’s “wobble.” This “wobble” refers to where the Earth’s imaginary axis points to arbitrary areas in space. Over about 23,000 years, the axis will complete a circular pattern where it points to different stars in the sky. A common star that is used for reference for this is Polaris, the north star. 

This image shows the current phase of “wobbling” of the Earth, compared to the future “wobble” phase of the Earth (Credit: Edward Hahn).

   How do these changes in the orientation of the Earth relate to our current problem with climate change? In order to answer this question, we can use the history of Earth’s climate and past CO2 levels in order to understand how we are impacting the natural cycles of change in the global temperature as well as atmospheric CO. Starting at 400,000 years ago, we see from the graph below that Earth’s temperature follows a pattern that oscillates up and down constantly, as do the CO2 levels of Earth. The dips in the graph represent ice ages, while the peaks represent warm interglacial periods.

This graph demonstrates the relationship between CO2 levels and temperature and how they change over time (credit: Environmental Dense Fund). 

​   From the graph, it is evident that CO2 has a strong correlation with the temperature of the Earth, and that CO2 levels are higher than they have ever been in Earth’s recent history. The alarming spike in recent years in CO2 can lead to the conclusion that temperature will also spike like it has in the past. The problem with climate change becomes clear when we closely inspect the cycle’s pattern. The Milankovitch Cycle’s pattern indicates that we should expect to experience falling global temperatures soon, but there is no sign that we will be experiencing any global declines in temperature in the foreseeable future. There is more work to be done in climatological research to discover what impacts humans have had or may have on the planet, and what measures may be taken to avoid potentially dangerous temperature changes. 

​To learn more about other global climate topics, be sure to click here!


© 2018 Weather Forecaster Cole Bristow