Saturday, September 24, 2005

Climate Change-Facts and Impacts (Part 1 of 4)

Climate Change: Facts and Impacts

Ø Is it happening, is it human caused?

Human induced Climate Change is the more accurate of two terms, the other being Global Warming. The importance of this is that in a complex system such as earth’s atmosphere a general warming does not necessarily lead to warming everywhere, it leads to changes in climate throughout the world, a redistribution of an increased amount of energy in a far from uniform manner. The two primary questions you might ask about what I have just said are:

1. Do we know for sure that the climate is changing?

2. Couldn’t this be as a result of natural variation in the climate system?

Climate Change was in fact predicted back in 1894 by the famous Swedish chemist Svante Arrhenius. The reason for this is that it was well known even back in 1894 that carbon dioxide is produced by burning fossil fuels and that it absorbs strongly in the infra red region of the spectrum, but allows visible light to pass through

There is a natural greenhouse effect caused by water in the atmosphere and natural levels of carbon dioxide, if it weren`t for this the planet would be far colder than it is today, and life would probably be impossible. We know the levels of carbon dioxide in the atmosphere where stable at 270ppm for thousands of years before the industrial revoloution and they are now ate around 370ppm. The scope of the second question is therefore limited to quantification: is natural variation of a magnitude so great that the warming created by emissions of fossil fuel and deforestation derived carbon are not significant?.

The answer to this is no, we can distinguish a clear signal of human caused (anthropogenic) Climate Change for at least the last forty years, this is found across all climate models and is superbly illustrated by the Intergovernmental Panel on Climate Change in there Third Assessment Report (TAR). On a planet entirely covered by solid ground the warming effects of carbon emissions would be felt very rapidly. Earth however is covered largely by water and there is therefore a lag before atmospheric warming is seen to the expected degree. This is why even if we stopped emitting carbon now, there would still be a significant further warming.

Ø There is some climate variability though, how much?

This question has two important parts which need addressing:

1. What are the timescales of natural variability and of what magnitude are these variations.

2. Abrupt climate change its dangerous to whether or not it is natural.

Human civilization has developed in a particularly stable climatic period, and we have benefited enormously from this fact. The figure below shows how the climate has varied over the past hundred and fifty years. Based on these historical temperature data and carbon dioxide concentrations models have been used to project forward the likely increases in temperature.


When compared to human lifetimes climate change tends to be relatively slow, the rate of the coming change is one of the most worrying things to many people, particularly ecologists and humanitarian charities who know that both ecosystems and human societies take time to adapt to change. The diagram below (fig.4) shows the relative stability of the climate system over the last ten thousand years.

You can just about see times such as the ‘medieval warm period’ that allowed the Vikings to colonise Greenland, and the ‘little ice age’ which drove them out, hitting Viking civilisation in general very hard. This leads on to the second point that needs addressing. What is shown on this diagram is the small magnitude variation within a ‘climatic mode’ that is still capable of brining down civilizations such as the Vikings, Assyrians, Maya and Anasazi. It is hoped however that this is the kind of climate change that we are going to see in the future, there will be a greater degree of warming than seen in the past ten thousand years but hopefully it will continue to be a linear process, a given amount more carbon dioxide producing a given rise in temperature. Unfortunately more extreme changes can occur.


The younger Dryas event is the most recent and best-studied example of abrupt, or non-linear, climate change. The details aren’t all known, but it is clear that the atmosphere/ocean system changed state in some dramatic way: a small variation became amplified. To clarify, a certain degree of Climate Change is happening and will continue, however there is potential for dramatic climate change of unknown severity to occur. Richard Alley is a paleo-climatologist from Penn State University, he studies ice-cores for information on past climate, and his team has found that:

“Sometimes a small push has caused the climate to change a little, but other times, a small push has knocked Earth’s climate system into a different mode of operation, brining new weather patterns to Earth in only a few years or decades”

(A push being any change; solar radiation, carbon dioxide, methane etc..)

How much are we ‘pushing’ the system, what are the observed and predicted changes in carbon dioxide concentration in the atmosphere? The answer to this is that we are emitting carbon dioxide at an alarming and increasing rate and this may well continue without concerted global action by all countries, including the USA as the most polluting of all, on a per capita and absolute basis. For a comparison of carbon dioxide concentration over the last 160’000 years, look at the graph below.

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This is part 1 of 4 in a series of articles on climate change part 2 of 4 is here.

1. Basic Science of Climate Change.
2.Effects of Climate Change so Far.
3.Future impacts of Climate Change.
4. Level of emmisions reductions required.

The series a a whole can be downloaded in PDF fromat (5MB) or word format (10MB)
If you would like to synidicate the article you are free to, the word doc is available for this purpose, i would however appreciate it if you would inform me of this.

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