Is Climate Change Natural?

The debate about climate change is not whether the temperature of the earth is rising, it is about whether humans have caused this and whether humans can thus reverse it. In other words is it a natural phenomenon that we have to accept, or not? A few weeks ago ‘The Express’ published an article with 100 reasons why climate change is natural:

http://www.dailyexpress.co.uk/posts/view/146138

This was quickly followed by an article in the ‘New Scientist’ describing why Climate Change is not natural:

http://www.newscientist.com/blogs/shortsharpscience/2009/12/50-reasons-why-global-warming.html?DCMP=OTC-rss&nsref=online-news

Of course neither article claims global warming is entirely natural or entirely due to humans, but the question is whether human activity has a significant impact or not. If it does then we must change our lifestyles, if it doesn’t then we must eat drink and be merry..

For me, graphs like the one below are convincing. The red line appears in all three graphs and is the earth’s temperature and no one will disagree that this is rising. The first graph also shows a model in grey of natural effects on temperature, such as solar flares, in the second graph the grey line instead shows a model of solely human effects on temperature due to CO2 emissions, and in the third graph the grey line is a model combining the two.


This begs the question about what happened before 1850, as 1850 was a comparatively short time ago. The graph below shows the temperature of earth and compares it with the CO2 in the atmosphere at that time:

Human activity has only really caused a rise in CO2 emissions since the Industrial Revolution, as burning wood is carbon neutral, hence shown in the graph below is the effect of us in the form of solids – coal, liquids – oil and gas.
I suppose my conclusion is that the level of CO2 in the atmosphere causes the temperature to rise or fall and that since 1850 we have put a lot of CO2 into the atmosphere, hence we might expect to see the rapid increases in temperature we are experiencing:
1 reply
  1. Richard Riggs says:

    Hi Lesley

    The IPCC says the temperature rise in recent decades is real, beyond doubt, but as for whether it is caused by greenhouse gases, they say it is very likely, defined as 90% probability.

    I’m a bit cautious about comparing past variations as a way of deciding whether the present rise is natural. I prefer your last sentence. CO2 concentration is now 1/3 higher than the pre-industrial level, and that is completely unnatural. So what happened in the past is no guide to the future. Basic physics says there will be warming, the only question is how much.

    As a result of a letter I had published in Physics World, I have been in correspondence with a couple of sceptics. It prompted me to start on an article under a title like “climate change for non-scientists”. It’s coming along quite nicely but I’m not sure what’s the best thing to do with it.

    Reply

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