Unwavering Cycles of Earth's Climate

  

The Unwavering Cycles of Earth's Climate

To truly understand our planet's climate, we need to zoom out and look at the bigger picture, a picture that spans not just decades, but hundreds of thousands of years.

Table of Contents

🌦 A Frozen History

🌦 The Milanković Hypothesis

🌦 The Human Story

🌦 The Dawn of Agriculture

🌦 A Look Beyond Today

🌦 The Image

A Frozen History

The most profound record of these cycles is a silent one, found in the vast, deep ice sheets of places like Antarctica. Scientists there drill down to collect 'ice cores', which are essentially frozen time capsules. As snow falls year after year, it compacts into distinct layers of ice, trapping tiny bubbles of ancient air and other atmospheric particles. By analysing the chemistry of the ice and the composition of the air bubbles, we can get a precise record of the temperature, atmospheric gases, and even volcanic activity from when that snow first fell. The Vostok ice core, for instance, provides a continuous climate record stretching back an incredible 420,000 years.

The Milanković Hypothesis

The data from these sources was used to finally prove a theory that was proposed decades earlier. In the 1920s, a brilliant Serbian geophysicist named 'Milutin Milanković' put forward a hypothesis that long-term climate cycles were driven by predictable changes in Earth's orbit. He identified three key cycles: the changing shape of Earth's orbit, the wobble of its axis, and the slight change in its axial tilt. While his ideas were initially ignored, they were proven to be remarkably accurate in the 1970s and 80s when the ice core data became available, showing that the cycles of past ice ages matched his calculations almost perfectly.

The Human Story

This cyclical nature of the climate has had a profound impact on the human story. Roughly 12,000 years ago, at the end of the last ice age, the planet's climate became warmer and more stable. This new period allowed for a revolution in human life: the development of agriculture. This abundance allowed people to settle in one place rather than constantly following food sources. Over time, these settlements grew into villages, then towns, and eventually, the first great civilisations.

The Dawn of Agriculture

With more consistent weather and higher temperatures, humans were able to domesticate plants and animals, leading to reliable food surpluses for the first time. With food security, not everyone had to spend their days hunting or gathering. This led to specialisation of labour, allowing people to become artisans, priests, and builders. It was this stability and wealth that provided the resources and collective energy to build immense monuments that we still marvel at today, such as Stonehenge and the pyramids of ancient Egypt.

A Look Beyond Today

The data clearly shows that the Earth has regularly swung between cold, glacial periods (ice ages) and much warmer, interglacial periods. These transitions didn't happen overnight; they were massive, gradual shifts that took thousands of years to complete. The planet has been both much hotter and much colder than it is today, all as part of its natural rhythm. So, when we consider the climate of our present day, it's not the whole story. It's a single moment on a very long timeline. It's an interesting part of a vast and complex natural process that has been going on long before humanity existed and will continue to do so long after we are gone. When viewed from this perspective, today’s climate can be seen not as an end, but as a fascinating point in the ongoing, dynamic history of our planet.

The Image

This image was produced by Robert A. Rohde from publicly available data, and is incorporated into the Global Warming Art project. - Eigenes Werk.
This figure shows the variations in Earth's orbit, the resulting changes in solar energy flux at high latitude, and the observed glacial cycles. According to Milankovitch Theory, the precession of the equinoxes and the apsides, variations in the tilt of the Earth's axis (obliquity) and changes in the eccentricity of the Earth's orbit are responsible for causing the observed 100 kyr cycle in ice ages by varying the amount of sunlight received by the Earth at different times and locations, particularly high northern latitude summer. These changes in the Earth's orbit are the predictable consequence of interactions between the Earth, its moon, and the other planets. The orbital data shown are from Quinn et al. (1991). Principal frequencies for each of the three kinds of variations are labeled. The solar forcing curve (aka "insolation") is derived from July 1st sunlight at 65 °N latitude according to Jonathan Levine's insolation calculator [1]. The glacial data are from Lisiecki and Raymo (2005) and gray bars indicate interglacial periods, defined here as deviations in the 5 kyr average of at least 0.8 standard deviations above the mean.