The anatomy of climate (part 1)

The Earth’s climate is constantly changing. Everyone has heard of ice ages: it used to get very cold on Earth, and vast areas were covered with ice for thousands of years. There were also times when the whole planet turned into tropics, and it was humid and warm even near the poles. To find out how the climate has changed, people study plants and animals of the past, deposits in the soil and at the bottom of the oceans, and isolate gas bubbles from years of ice.

But is it possible to know what the climate will be like in the future? Today, we will tell you what the Earth’s climate depends on and how to predict it. This text is divided into two parts. In the first part, we will talk about climate in general and how it is affected by the Sun and other celestial bodies. Let’s begin!

In general terms

The climate is the «average weather.» It includes all meteorological characteristics, like temperature, precipitation, and wind. They can be averaged over any area: «the climate of France», «the climate of Europe», or «the climate of the Earth». The period that we average should not be too short. Today, the climate is estimated for 30 years, but you can look at a longer period: for example, «the climate of the Holocene» (the last 12 thousand years). In general, «climate» is a very diverse concept. But most often, when we talk about climate, we mean the average temperature for 30 years, because, in this case, the trends are more obvious, and all characteristics are easy to observe.

The climate can be predicted in the same way as the weather: with computers and equations. Here is roughly how it works:

Find out what natural processes affect the climate
Determine the physical laws by which these processes «work»
Prepare a mathematical model and run it on a supercomputer

The task is very complicated because of the interconnection of many processes on the surface of the Earth and in its atmosphere, as well as the influence of the Sun and other celestial bodies. In general, the climate can be compared to a living organism, like a human being. Our condition depends on both external conditions and what is going on inside the body. Let´s imagine that the Earth is a person, and the climate is its state of being.

Weather Outside

For us to be comfortable, good weather is very important: it shouldn’t be too hot or too cold. For our planet, «weather» is the intensity of the sun’s radiation, because most of the Earth’s heat comes from the Sun.

Since the birth of the Sun, the intensity of its radiation has been slowly increasing, and the Earth receives more and more heat. We know this from observations of other stars and from the history of the Earth itself, and we can make predictions.

But there are also cyclical changes in the Sun, that is, alternating periods of increased and decreased activity. There are several such cycles: one is an 11-year cycle, another is 22 years, a century, and millennia. We are also forecasting based on them, but we still do not fully understand the reasons for their occurrence.

How to dispose of energy

But even with the same solar activity, the climate can be very different, depending on how the sun’s energy is distributed around the planet. There are two main processes this depends on.

Milankovitch cycles

These are slow, changes in the parameters of the Earth’s orbit, occurring over many thousands of years. The orbit in which the Earth revolves around the Sun is not a circle (as we always imagine), but an oval. It constantly changes shape: it either shrinks and becomes almost a circle, or stretches out. And the Sun is never in the center of this oval, but closer to one of its edges.

Valerya Milovanova / Windy.app

Now take the northern hemisphere of the Earth, and imagine this coincidence: winter comes, and the Earth is far away from the Sun. It would be colder than usual. And in summer, the Earth is close to the Sun, and summer is hotter. The climate has highcontrasts. At the same time, in the southern hemisphere, it is the opposite: winter is very warm, and summer is cold, the climate has evened out.

We should also remember that the axis of rotation of the Earth is tilted by about 23° to the plane of the orbit, and, because of this, winter and summer alternate. But over the millennia, this angle changes cyclically, too. As the angle increases, the seasons become more pronounced; as the angle decreases, they become less pronounced.

Valerya Milovanova / Windy.app

Milankovitch cycles happen because of the influence of the Moon, the Sun, and other planets on the Earth. We understand this well, and can make predictions based on it. For example, now the shape of the orbit is close to a circle (and continues to strive for a circular shape), and in January, the Earth is slightly closer to the Sun than in June. The climate is fairly flat now, and will not change anytime soon.

Tectonics

Continents are constantly moving, changing the face of the Earth. As the continents move, air circulation, sea currents, and the entire climate change.

Here, too, the Earth goes through cycles: the continents come together to form one giant supercontinent, and then they diverge again.

Valerya Milovanova / Windy.app

The Earth’s climate strongly depends on where the continents are located. For example, if they all join together at the equator, the Earth will get very warm. And if the continents unite at the pole, they will be covered by an ice cap, as Antarctica is now, and very cold times will ensue.

If you look at a map of the world, you’ll see that all the continents have now split apart, and this contributes to a milder climate. In the next 200 million years, the continents may reunite, but we don’t yet know exactly where or when that will happen.

Solar activity and Milankovitch cycles are the two main «external» processes affecting the Earth’s climate. And in the next text, we will talk about how the Earth can change its own climate.

Text: Eugenio Monti, a meteorologist and a climatologist

Cover photo: Simon Maage / Unsplash

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