Climate Change – the simple facts

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As I mentioned in an earlier post, climate change is one of those topics on which it’s hard for the layman to make a judgement. Whom do you believe? Do you trust the pollies to know all about it and therefore feel comfortable following their lead?

What I think

I’ll declare my position up front: A HUGE body of research exists on climate change, and there is consensus among the experts in the appropriate fields that there is a risk to our society and the planet if we continue on our current course.

The issue is not whether our activities are changing the climate, but to what extent.

I vote we mitigate the risk, rather than roll the dice. It’s as simple as that.

The problem here is finding the reliable sources – those who are qualified, have done the work, and have no reason to deceive us. Earlier I deliberately said ‘experts in the appropriate fields’ because there are many who claim to be experts, but don’t have the necessary qualifications or experience. For example, a prominent Australian ‘expert’ and climate skeptic, is a mining company geologist, and a director of a number of mining companies and so has more than an academic interest. More importantly, his field of expertise is not climate. So we need to be very careful about which sources to trust when forming a view. Hence the post I quoted earlier.

Because this field is so complex, the Australian Academy of Science has produced a summary of the key information (access here: ISBN 085847 286 4, “The Science of Climate Change: Questions and Answers”). In this post, I’m going to try to summarise the big picture, as agreed by a consensus of appropriately qualified experts. If anyone is interested in exploring further, I’ll do subsequent posts exploring key aspects of the issue in more detail.

What we know

In a nutshell, the earth’s climate is changing – the global average temperature has increased over the past century, and that this is due to human-induced increases in the emissions of greenhouse gases. How can we say this? There are four lines of science behind this:

1. Greenhouse gases trap heat

We have known for a century that a gas like CO2 traps heat, and that as the concentration of CO2 in the atmosphere increases, the temperatures at the Earth’s surface will rise. This much is not in dispute, even by the most vocal of climate skeptics.

2. Small changes can have big impacts

Geological records tell us that the planet has gone through around ten major ice-age cycles over the last million years, and that the last few thousand years have been fairly stable. However, we can also see from the record that minor influences can result in swift changes in climate (eg – meteor impacts). What does this mean? It means that seemingly small changes in the balance of things can have dramatic effects, and so puts beyond doubt that the contribution of humans could disturb the balance.

3. We have increased greenhouse gases in our atmosphere

Measurements in the last couple of hundred years prove a clear rise in the concentration of CO2 since man industrialised the planet. These measurements also tell the story that the Earth’s surface is warming along with this rise in CO2, and that this, in turn, is causing other environmental changes.

4. Climate models

With a grasp of physical principles, and armed with records from the recent and distant past, we are able to build predictive models. These models tell us that the average temperature will continue to increase if we do not reduce the levels of CO2 in the atmosphere.

In summary, our models predict that, by 2100, increases of between 2°C and 7°C. At the low end of the band, we will get a very different world which will require significant change in the way we humans live. At the high end, the world will be greatly transformed, and because it will happen so quickly, many societies and species will perish. (Note – this prediction is now a number of years old. More recent modelling shows that the high end of this range is becoming more likely.)

So, to string these lines of evidence together:

  1. Greenhouse gases like CO2 trap heat, and this can be shown to be the case in the atmosphere. Check.
  2. Small changes in the atmosphere can cause large changes in the climate. Check.
  3. Human activity has injected additional CO2 into the atmosphere, which has caused a small change in the concentration of that gas, and we have observed large changes in the environment, like rising global average temperatures. Check.
  4. Plugging what we know into some predictive models tells us that these rising global average temperatures will have effects on our society as we know it, to a greater or lesser extent. We specify these predictions in terms of likelihood, not certainty, but the likelihood is high. Check.
  5. Therefore, the inescapable conclusion is that human-induced climate change is real, and that it is likely that it will change our society dramatically in the next 50 to 100 years. If we are prepared to take whatever changes come along, then let’s do nothing. This means accepting submerged coastlines and islands, dislocating millions of people and costing hundreds of billions of dollars, not to mention changes in habitats etc. On the other hand, we can invest a few billions now, and help to preserve our environment and society as we wish.

Of course, no model is perfect, and many assumptions need to be made. Scientists are generally careful to make conservative estimates for particular parts of the model. As I said, the word ‘probably’ must be used with the 2-7°C thing. It could be a bit less, or a bit more. But it will be something, and that’s where rolling the dice comes in.

With apologies to Clint Eastwood, how lucky do you feel this century?


2 thoughts on “Climate Change – the simple facts

    Climate change for dummies « rationalbrain said:
    May 7, 2011 at 5:21 pm

    […] while back I tried to summarise the key factors in climate change science – to try and boil down a pretty complex area into […]

    Must See: Science Under Attack « rationalbrain said:
    August 10, 2011 at 9:50 pm

    […] – hence rising global temperature. Simple. (If you want to revisit the climate discussion, here’s my attempt at simplifying the discussion. And a nice video on the subject here. There’s also this and […]

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