World Temperatures and Ice Ages

Earths ever changing Climate

The main reason for the existance of climatic regions on our planet is the tilting of the Earths vertical axes and the elliptic rotation of the Earth around the sun. This causes the amount of incoming solar radiation to vary throughout a year. As a result we have four seasons each lasting around 90 days.

As said, the orbit of the Earth around the sun is not a perfect circle, this too is causing variations in the seasons and weather. It is more like an elliptical and during Januari the Earth is closest to the sun (perihelion). And even this ellipse is also not stable causing more changes in the incoming solar radiation (insolation).

In this text we will delve a bit deeper to understand the result of all these variables and we will see the effects of them on our climate.

Climate changes

Before we start, lets establish one thing: the climate on this planet has never been stable and never will. It changes daily, weekly and so on. At the moment we are living between two ice ages in what is called a interglacial warm period (holocene) and we are nearing the end of it, so enjoy while it lasts. It could change within a short period of time dropping us into a new ice age.

Climate changes are mainly caused by the following phenomena: astronomic, atmospheric and tectonic influences. Variations in the orbit around the sun, changes in our atmosphere and the constant moving of the tectonic plates all have an influence on our climate.

And we see the results of those changes when we drill out cores of ice from permanent glaciers to examine them. See image on top of the page from the Vostok ice core.

Astronomic Cycles

The axial tilt of the Earth varies between 22,1° and 24,5° (23,5° at the moment) in a period of 41000 years. Also, due to precession the tilt moves around the real vertical axes. This is caused by the gravitational pull of the moon and the sun (both equal) and takes some 26000 years.

The elliptical orbit of the Earth around the sun is also influenced by the gravitational pull from planets as Jupiter and Saturn with a cycle between 95000 and 125000 years. This eccentricity would not exist if Earth was the only planet orbiting the sun. This yearly orbit also has a precession effect (apsidal precession) with a cycle of around 23000 years. The orbit of the Earth also moves up and down (inclination) with a period of 70000 years and variations of the invariable plane cause cycles of 100000 years, very similar to the Ice Age period.

All these variations in the movement of planet Earth are called Milankovitch cycles as theorized by Milutin Milankovic in his study of the ice ages and variations of the Earth's orbit with effect on climate changes. Where he found some remarkable coincidences!

Ice Ages

The Earth's climate warms and cools by a number of different cycles, causing variation in the amount of insolation received. The result is that Earth receives a varying amount of heat (energy) and the average temperature will either drop or rise as a result of these cycles and the climate will either be cool or be warmer.

We all remember the paintings in the galleries from the Middle Ages, they show us that the Earth was in a cooler period between about 1400 AD and 1850 AD. Even in this short period the temperature fluctuated again caused by a 40 year cycle. This "Little Ice Age" was known for short growing seasons with a drier climate and cold winters as can be seen on the Medieval paintings. The drop in global temperatures was only a modest 1/2°C, and the effects of this global cooling cycle were felt more in the higher latitudes, closer to the poles.

The climate on Earth has been warming up since the last Ice Age (Pleistocene), some 18000 years ago. In fact, every 100000 years the climate Earths warms up and we are now almost at the end of the current warm interglacial period and probably heading for a new Ice Age.

Atmospheric influences

Greenhouse Effect

Our atmosphere is a layer of gases surrounding our planet and it is kept there solely by its gravity caused by the Earths magnetic field. It contains some 78% Nitrogen, 21% Oxygen, 0,93% Argon, 0,039% Carbon Dioxide (CO₂), minute amounts of other gases and a variable amount (on average between 0-4%) of water vapor (resulting in clouds and rain). This complete mixture is known to us as air.

Greenhouse effect

Wikipedia: "Existence of the greenhouse effect as such is not disputed. Naturally occurring greenhouse gases have a mean warming effect of about 33°C (59°F), without which Earth would be uninhabitable. On Earth, the major greenhouse gases are water vapor, which causes about 36-70% of the greenhouse effect (not including clouds!); carbon dioxide (CO₂), which causes 9-26%; methane (CH₄), which causes 4-9%; and ozone 3-7%". Without this greenhouse effect there would be no life on this planet.

Greenhouse effect keeps the Earth warm enough to live. But clouds, volcanic dust, atmospheric particles, snow and the arctic caps reflect heat back into space (Albedo effect) and cools it off thus maintaining a balance fit for live as we know it.

Tectonic movements

Shifting continents and the subsequent seafloor spreading cause a change in ocean currents (think El Nino) influencing the climate world wide. Vulcanic eruptions are a good example of tectonic movement, as you will usually find vulcano's where two tectonic plates meet.

These vulcanic eruptions emit enormous amounts of gases in the atmosphere and the soot and ashes are able to block the sun, causing worldwide temperature drops.

It is safe to say that the amount of man made CO₂ in the atmosphere (about 3%) doesn't really contribute to the greenhouse effect. Its just a small drop in the scheme of bigger things that are happening.