We're in the grip of autumn, and it's getting colder. Are we moving towards an ice age, one of the readers wonders.
The fast Danish summer is over. Leaves fall from trees, birds fly south, it gets darker and, of course, colder too.
Our reader Lars Petersen from Copenhagen began to prepare for the cold days. And he wants to know how seriously he needs to prepare.
“When does the next ice age start? I learned that ice ages and interglacial periods alternate regularly. Since we live in the interglacial period, it is logical to assume that the next ice age is ahead of us, isn't it? - he writes in a letter to the Ask Science (Spørg Videnskaben) section.
We in the editorial office shudder at the thought of the cold winter that lies in wait for us at that end of autumn. We, too, would love to know if we are on the verge of an ice age.
The next ice age is still far away
Therefore, we addressed to Sune Olander Rasmussen, a professor at the Center for Basic Research of Ice and Climate at Copenhagen University.
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Sune Rasmussen studies the cold and gets information about the weather of the past, the storm of Greenland glaciers and icebergs. In addition, he can use his knowledge to play the role of "predictor of ice ages."
“For the Ice Age to come, several conditions must coincide. We cannot predict exactly when the ice age will begin, but even if humanity did not further influence the climate, our forecast is that the conditions for it will develop in 40-50 thousand years at best,”Sune Rasmussen reassures us.
Since we are still talking with the "predictor of the ice age", we can get some more information about what these "conditions" are in order to understand a little more about what the ice age really is.
This is what an ice age is
Sune Rasmussen says that during the last ice age, the average temperature on earth was several degrees lower than it is today, and that the climate at higher latitudes was colder.
Much of the northern hemisphere was covered in massive ice sheets. For example, Scandinavia, Canada and some other parts of North America were covered with a three-kilometer ice shell.
The enormous weight of the ice cover pressed the earth's crust a kilometer into the Earth.
Ice ages are longer than interglacials
However, 19 thousand years ago, changes began to occur in the climate.
This meant that the Earth gradually grew warmer, and over the next 7,000 years, it was released from the cold grip of the ice age. After that, the interglacial began, in which we are now.
In Greenland, the last remnants of the shell came off very abruptly 11,700 years ago, or 11,715 years to be precise. This is evidenced by the research of Sune Rasmussen and his colleagues.
This means that 11,715 years have passed since the last ice age, and this is a completely normal length of the interglacial.
“It's funny that we usually think of the Ice Age as an 'event', when in fact it's just the opposite. The average ice age lasts 100 thousand years, while the interglacial period lasts from 10 to 30 thousand years. That is, the Earth is more often in an ice age than vice versa."
“The last couple of interglacial periods only lasted about 10 thousand years, which explains the widespread but misconception that our current interglacial period is approaching the end,” says Sune Rasmussen.
Three factors influence the possibility of the start of an ice age
The fact that the Earth will plunge into a new ice age in 40-50 thousand years depends on the fact that the Earth's orbit around the Sun has small variations. Variations determine how much sunlight hits which latitudes, and thus affects how warm or cold it is.
This discovery was made by the Serbian geophysicist Milutin Milankovic almost 100 years ago, and therefore it is known as Milankovic Cycles.
Milankovitch cycles are:
1. The orbit of the Earth's rotation around the Sun, which changes cyclically about once every 100,000 years. The orbit changes from nearly circular to more elliptical and then back again. Because of this, the distance to the Sun changes. The further the Earth is from the Sun, the less solar radiation our planet receives. Also, when the shape of the orbit changes, so does the length of the seasons.
2. The tilt of the earth's axis, which fluctuates between 22 and 24.5 degrees in relation to the orbit of rotation around the sun. This cycle covers approximately 41,000 years. 22 or 24.5 degrees - it seems not such a significant difference, but the tilt of the axis greatly affects the severity of the different seasons. The more the Earth is tilted, the greater the difference between winter and summer. Currently, the tilt of the earth's axis is 23.5 and it is decreasing, which means that the differences between winter and summer will decrease in the next thousand years.
3. The direction of the earth's axis relative to space. The direction changes cyclically with a period of 26 thousand years.
“The combination of these three factors determines whether there are prerequisites for the beginning of the ice age. It is almost impossible to imagine how these three factors interact, but with the help of mathematical models we can calculate how much solar radiation is received at certain latitudes at certain times of the year, as well as received in the past and will receive in the future,”says Sune Rasmussen.
Snow in summer leads to an ice age
Summer temperatures are especially important in this context.
Milankovitch realized that in order to have a prerequisite for the start of the ice age, summers in the northern hemisphere must be cold.
If the winters are snowy and most of the northern hemisphere is covered with snow, then the temperatures and the number of hours of sunshine in the summer will determine whether snow is allowed to remain throughout the summer.
“If the snow does not melt in summer, then little sunlight penetrates the Earth. The rest is reflected back into space with a snow-white blanket. This exacerbates the cooling that started due to the change in the Earth's orbit around the Sun,”says Sune Rasmussen.
“Further cooling brings more snow, which further reduces the amount of heat absorbed, and so on, until the ice age begins,” he continues.
Likewise, a period of hot summers leads to the end of the ice age. The hot sun then melts the ice enough so that sunlight can again hit dark surfaces like soil or the sea, which absorb it and heat the Earth.
People are delaying the next ice age
Another factor that matters for the possibility of an ice age beginning is the amount of carbon dioxide in the atmosphere.
Just as snow, which reflects light, intensifies ice formation or accelerates its melting, the rise in atmospheric carbon dioxide from 180 ppm to 280 ppm (parts per million) helped lift the Earth out of the last ice age.
However, since the beginning of industrialization, people are constantly engaged in further increasing the share of carbon dioxide, so now it is almost 400 ppm.
“It took nature 7,000 years before the end of the ice age to raise the share of carbon dioxide by 100 ppm. Humans have managed to do the same in just 150 years. This is of great importance for whether the Earth can enter a new ice age. This is a very significant impact, which means not only that the ice age cannot begin at the moment,”says Sune Rasmussen.
We thank Lars Petersen for the good question and are sending winter gray t-shirt to Copenhagen. We also thank Sune Rasmussen for the good answer.
Did you know?
Scientists always talk about an ice age only in the northern hemisphere of the planet. The reason is that the southern hemisphere has too little land on which a massive layer of snow and ice can lie.
Excluding Antarctica, the entire southern part of the southern hemisphere is covered with water, which does not provide good conditions for the formation of a thick ice shell.
Kristian Sjøgren
