In the 1920’s a Serbian geophysicist and astronomer called Milutin Milankovitch suggested that long term variations in how the Earth travels in space may affect climate change because of the effect these changes have on the amount of solar radiation that hits the Earth’s surface. He recognized three long term cycles and these cycles are now referred to as Milankovitch Cycles.

Milankovitch Cycles

The three cycles are the variability of the Earth’s orbit, the position of the Earth when it’s closest to the sun, and the amount the Earth tilts on its axis.

Eccentricity of the Earth’s orbit

The first cycle is the variability or eccentricity of the Earth’s orbit which ranges from nearly circular to more elliptical and back every 90,000 to 100,000 years.

Milankovich cycles - orbit shape

Longitude of perihelion

The second cycle refers to the position of the Earth when it is closest to the sun referred to as the longitude of perihelion.  At the present time, the Earth is closest to the sun in its orbit during the southern hemisphere’s summer and furthest away from the sun during the northern hemisphere summer. This changes every 10,000 or so years, making the complete cycle around 21,000 years.

Obliquity of Axis

The third cycle refers to the “lean” or obliquity of the Earth on its axis. This lean changes the Earth’s tilt from 21.8° (closest to upright) to 24.4° (most inclined). The full cycle from 21.8° back to 21.8 ° takes about 40,000 years.

 

 

 

Where are we in the cycles now?

At the present time, the earth’s orbit is nearly circular and becoming more circular, the longitude of perihelion gives the southern hemisphere warmer summers (and cooler winters) than the northern hemisphere and the obliquity is decreasing tending to decrease the differences between the seasons.

 

So what does it really mean for climate change?

The Milankovitch cycles do have an influence on our climate, and there seems to be a good correlation between the cycles and the evidence we have for Earth’s ice ages.  However, there are times that the cycle prediction has failed, or when major climate events have taken place for which the cycles can’t explain.  This may mean that other factors, like atmospheric chemistry (greenhouse gases for example), volcanic eruptions, location of continues due to plate tectonics, the size of ocean basins, and ocean currents may play a stronger influence.

Milankovitch cycles – the Earth in space and climate.

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