*Tiptoes back in*

So…it has been a while.  You know how it goes, you get caught up in something (in my case my final semester of my bachelor) and next thing you know, it is 8 months later, and then you feel awkward about returning after such a long break.

Anyway, I was asked if I would write up some posts on the IPCC report, so I thought it was as good a reason as any to get back into blogging!

I thought I should start out with an introduction to climate, as for me, the systems themselves are fascinating, and for a lot of people, climate is some abstract concept only heard in relation to carbon dioxide and climate change, when in reality, it is so much more.  I hope I can show you at least a little window into our awesome planet in this post.

Climate is defined as “The pattern of variation in temperature, wind, humidity, atmospheric pressure and other variables over a long period in a given region”

This is different from weather, which is the temperature, wind, humidity, atmospheric pressure etc at a given time in a specific location.

So, climate is “It is cold in Sweden”, weather is “It snowed today in Stockholm”.

The main factor affecting climate on Earth is the incoming solar radiation, which is unequally distributed across the surface of the Earth, being more concentrated at the equator, and more diffuse at the poles.
Solar Radiation Distribution. Image from

This means the atmosphere is heated more at the equator, and less at the poles.  As hot air rises, and cold air sinks, this unequal heating causes movement of air.  The air heated at the equator rises and moves towards the poles, whilst the cooler air moves towards the equator to replace the rising air.

This results in loops of air circulation, which are known as Hadley cells in the tropical regions (near the equator), Ferrel cells in the mid latitudes, and polar cells at the poles.

Global Atmospheric Circulation Cells. Image from wikipedia

In the areas where the air in the Hadley cells is descending, we find desert regions, this is due to the air being cooler, and containing less water than the warm, rising air at the equator.

These cells of circulating air play an important role in many of the large scale phenomena such as the monsoon circulation in Asia, formation of hurricanes, and the jet streams and trade winds, which are caused by a combination of the circulating air cells, and the rotation of the Earth.

The rotation of the earth means that air currents do not move in a straight line, but appear to rotate to the left, or right, depending on the hemisphere.  These two videos demonstrate the effect.  This first one is a simple experiment showing the phenomena:

This second video shows this effect in action, and is an animation of annual air circulation (I actually had an image of this as my desktop background for quite some time, as I really love the visualization).   You can see the deflection of the air currents, and the band across the equatorial areas known as the Intertropical Convergence Zone (ITCZ), which is where the northern and southern hemisphere air meets.

Next post in this series will cover the major climate zones on the planet, and some of the driving forces and phenomena in each of them.

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