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Climate change 3 - what is it?

Climate change 3 - what is it?

What is climate change?

In principle climate change is very simple, although modelling it scientifically gets very complex. The simple version is this: energy arrives at the earth's surface from the sun, and is radiated back out again by the earth into space.  That's all there is to it.  If the amount of energy arriving is greater than the amount of energy radiated out, then the planet warms up. If it's the other way round, if more energy is radiated out into space than arrives from the sun, then the planet cools down.

In the first case, with more energy coming in, the planet warms up and we get global warming. In the other case, when the planet is losing more energy than it receives, we'll be heading for an ice age.

The things that control the balance between energy coming in and energy going out are the greenhouse gases. There is a bit of variation n the energy coming from the sun, so there is a cycle there, but the main factor is the greenhouse gases, which include carbin dioxide, methane and water vapour. There is another factor, which is the colour of the planet. The more ice there is, the whiter the planet is, and therefore the more light is reflected out into space.  You will see this whiteness described as albedo - the greater the albedo, the more the planet is cooled. This is why once the earth enters an ice age, and a large proportion of the surface is white, it's really quite hard to get out of it again. It usually takes something like a volcanic eruption, which covers all the ice with darker volcanic ash, to bring the earth out of the ice age and start to warm up again.

The albedo is important, because as the planet warms up, the polar ice caps reduce is size, which accelerates global warming.  This can lead to a tipping point, meaning that once we've reached a point of too little ice, it hard to get it back again.  This is the opposite of an ice age, a period with a fixed higher temperature which is hard to reduce.

However before we get to the extremes of too much or too littl ice, there are the greenhouse gases to continue.  The main one that we know about is carbon dioxide, however it's also very important to consider methane, because this is a much more potent greenhouse gas than carbon dioxide. Various figures are quoted, and these can be misleading, becaus ethey are often quoted as averages. The fact is that in the short term methane is 80 to 100 times more potent than carbon dioxide as a greenhouse gas.

What does a greenhouse gas do?  It reduces the amount of energy being radiated out into space, therefore warming the planet. This is why it's called a greenhouse gas - just as the glass in the roof of a greenhouse traps the heat inside, greenhous egases trap heat close to the earth's surface and prevent it being radiated out again.

When considering carbon dioxide, there are two important figures to consider.  The first one is 280 ppm. This is roughly the Co concentration that was around prior to the industial revolution.  The earth'd carbon dioxide level had been stable at this figure for a very long time.

Since the industrial revolution mankind, firstly in England and then in the rest of the western world, started burning fossil fuels at an increasingly rapid rate,  firstly coal, and then petroleum. As a result of this the CO2 level gas increased to 400ppm. As the CO2 level goes up the earth starts to heat. At 40ppm it's heating quite significantly, and this is what is raising concerns.  What you have to remember is that just reducing your C emissions does not reduce the CO2 level in the atmosphere.  So if everybody in the world were able to move to zero carbon emssions, the CO2 level would just stay at 400ppm.

What about trees you ask? Dont they bring doen the CO2 level?  Yes they do, but only very slowly. Because as trees grow and absorb carbon, other trees are dying and releasing it. So ittakes a long time for the natural world to absorb all the carbon thats been emitted.  There are reasons which I won't go into here that suggest that the carbon that's been released from the fossil reserves beneath the eart's surface can never be put back there.

Therefore we have to assume that just stabilising carbon emissions at the present level is not good enough, we have to get the CO2 level to well below 400ppm. Ideally we have to get it back to the pre IR level of 280ppm.
Realistically this is not going to happen.  There is a graph of global CO2 level measured at the Mona Loa observatory in Hawaii, which shows the CO2 level rising year on year. Despite all the world's efforts to redice CO2 emissions.  The reality is they are not coming down.

There's a very good reason for this. Our civilisation, our way of life, our wealth, our health service, our ability to grow food and feed a high population all depend on burning fossil fuels. To expect a government to do something about this would be asking it to sacrifice the way of life, health and ultimately the survival of its population. No government is going to treat its voters in such a way, it would be far too unpopular.  Therefore CO2 emissions keep going up.


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