Question: why does the climate changes?

James Pope answered on 25 Jun 2012:

Hi oliwiabieber and karolinaparker

This is a brilliant question!

There are a number of reasons why the climate changes. The phase of glacial and inter-glacials which is the scientific name for the ice ages were caused by the changes in the orbit of the earth around the sun and in the changes in the angle the earth tilts towards the sun. These cycles, were discovered by a Serbian scientist called Mutin Milankovitch and he calculated all thos while under house arrest during World War I (he lived in Austria-Hungary, but was Serbian and Serbia was against Austria-Hungary so he was kept in his house to prevent him being a spy!).

These Milankovitch Cycles changed the amount of energy from the sun reached the Earth either due to the orbit of the Earth around the sun (either getting slightly closer or slightly further away) and the tilt of the earth towards the sun (whether the Earth leans towards the sun during it being furthest from the sun or nearest to the sun during the summer for that hemisphere).

This changes the amount of energy reaching the Earth’s surface from the sun and so allows ice sheets to grow over Canada and Europe (called an ice age or a glacial period) when it reduces or causing ice sheets to melt and retreat back to the polar regions and we enter an inter-glacial which has a warmer climate.

The other way that climate changes is due to greenhouse gases and the amounts of them in the atmosphere. The natural greenhouse effect, is how we can have life on Earth, it keeps us warm during the night, and without it the worlds average temperature would be about -15°C, compared to the 14°C it is today. When we add more greenhouse gases to this effect, we get a warmer average temperature.

There have been a couple of occasions during the last 65 milllion years where this has happened rapidly (over thousands of years) and completely due to nature, the biggest one was 55 million years ago, when a large release of methane frozen into the sea bed escaped to the atmosphere over 10,000 years and this caused 4-8°C of warming over 20,000-30,000 years!

but the entire climate from 65 to 2.8 million years ago, was one of higher than present day carbon dioxide levels and warmer temperatures. We had more carbon dioxide and therefore a warmer climate, but the temperature trends varied over the time. Some of this change was due to changes in the greenhouse gases but there are other things that change the climate that happened over the last 65 million years, such as changes to the flow of ocean currents. 33 million years ago, the separation of South America and Australia away from Antarctica, allowed a flow of water could form around Antarctica (called the Antarctic Circumpolar Current) which sealed Antarctica off from the rest of the world allowing an ice sheet to grow and this cooled the climate of the planet.

This image:

Shows data from the last 65 million years (when the Dinosaurs died) to the modern day. Grey dots are temperatures from fossilised plankton called foraminfera which are calculated by performing chemical analysis on the shells they grow during their lifetimes, which record the amounts of magnesium and calcium in the water which tells us about water temperature. The spike labelled PETM is the rapid warming event 55 million years ago.

One thing that looking at these changes in past climate can show us is that while the climate has changed naturally for hundreds of millions of years, it has never changed as rapidly as it is doing right now, partly because the greenhouse gases have never been emitted as quickly as this before. We are changing our climate faster than the best nature can offer and it is both incredible and very very scary.

If you want anymore guys, just leave a comment, I’m happy to add as much as you want me to!