In one of my previous blogs, I had described the changes in environment since the last ice age till the present day. I had stated that the changes in Earth’s orientation around the Sun (about 12,000 years ago) led to an increase in the solar radiation reaching the planet, causing an inevitable increase in global temperatures, ultimately leading to the end of the ice age. These collective effects of changes in the Earth's orientation in its orbit drive Earth’s long-term climate, triggering the beginning and end of glaciation periods. These cycles that determine the amount of solar energy that Earth absorbs from the sun, have been termed as Milankovitch cycles.
Milutin Milankovitch examined how these orientation variations affected the radiation reaching the top of the Earth’s atmosphere and found that it is responsible for up to 25% variation in the amount of solar insolation. Let’s understand these cycles that our lives literally revolve around.
The Milankovitch cycles includes:
· Eccentricity- shape of orbit which changes over time.
· Obliquity- angle at which Earth’s axis is tilted, varies as Earth orbits the Sun.
· Precession- direction at which the axis points, which is also variable.
These three cycles tend to change over time and collectively they bring about an overwhelming impact on Earth’s climate over a period of hundreds of thousands of years. Of these, obliquity was considered to be the most important factor in determining the climate because it affected the amount of insolation in higher latitudes during summer season. In simpler words, more tilted the axis of the planet, more radiations from the sun reach the poles, and more is the rate of retreat of ice at the poles. It is now clear that the Milankovitch cycle is responsible for Earth’s glacial and interglacial periods.
But I believe it’ll be brutal to blame climate change, a majorly human induced effect, on a natural cycle. How do we know that current global warming events are not a result of Milankovitch cycles?
Firstly, the Milankovitch cycles take really long periods to show effect on climate. We can confidently say that the rapid warming of the atmosphere since the pre-industrial era is indeed due to human activities. Interestingly, NASA satellite observations show that solar radiation reaching earth has in fact decreased over the past 40 years.
Also, Milankovitch cycles are only one of the factors that have driven the long time scale climate events. The span of ice sheets and carbon dioxide emissions, too, greatly impact temperature fluctuations. Statistically, the concentration of carbon dioxide has increased 47% since the onset of industrialization. In the past 20 years alone, there has been an 11% rise in carbon dioxide levels.
We can say that the anthropogenic activities are contributing to the Milankovitch cycles, speeding up climate crisis. Heating only due to solar radiation would warm up the troposphere as well as the stratosphere. However, satellite data reveals that the tropospheric temperatures have increased, but stratosphere has strangely cooled down. Scientists claim this variation is driven by greenhouse gases.
Most importantly, we are now in an interglacial period. Earth’s current position in the Milankovitch cycle should naturally indicate the start of the cooling period which leads to the next ice age. Instead what we are experiencing is a drastic rise in global temperatures. Not cool!
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