World Temperatures and Ice Ages
Earth's ever changing Climate, I
The main reason for the existence of climatic regions on our planet is the tilting of the Earth's 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 January 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).
Also variations in the output of the sun's energy will too have an effect on our climate in the long term.
In this text, and the next article, we will delve a bit deeper to understand the result of all these variables and we will see the effects on our climate realizing that climate science can never be settled as we learn more and more each day.
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 an 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.
Some are afraid that the Earth warms a couple of degrees, but the real danger is cooling. A warmer atmosphere can hold more CO2 which is used by plant life and this results in more food for humans. This is good!
There has, in 4.5 billion years of the Earth’s existence, always been climate changes. There have been ice ages, magnetic reversals, volcanic activity, tsunamis, earthquakes and a host of other natural events.
Climate changes are mainly caused by the following phenomena: astronomic, atmospheric and tectonic influences. Variations in the orbit around and output of the sun 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.
The axial tilt of the Earth varies between 22,1 ° and 24,5 ° (its 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 (apostle 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 Milankovitch 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!
More on this subject in the next off-site article from WUWT: The effects of irregularities in the Earth’s orbit.
Recent Warm Periods
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.
In the Middle Ages there was a warming period (MWP) where the average temperature was higher than today, even with a 35 % lower CO2 level. So there it is: CO2 has nothing to with warming!
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 some of the Medieval paintings.
Greenland GISP2 Ice Core Temperatures
The drop in global temperatures was only a modest 2 °C, and the effects of this global cooling cycle were felt more in the higher latitudes, closer to the poles. Move the mouse over the image to see global temperatures 10000 years into the past.
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 warms up and we are now almost at the end of the current warm and cozy interglacial period and probably heading for a new Ice Age.
At the moment we are in an interglacial period, in between two ice ages. Enjoy while it lasts as human kind prospers only while its warm! More detailed information in the next off-site link from WUWT about the paleo climate.