The climate is changing, and we're partly responsible. It's important to understand how much of an effect we're having to be fully able to do something about it.
Note: "Global warming" and "Climate Change" are almost interchangeable in this field. Neither perfectly explains exactly what's going on, but I'm quite likely to switch back and forth between the two in the attempt to get the point across. Until we can all agree on a perfect expression, I will use the common terminology, which everyone is familiar with, and understands.
What Is The Atmosphere Made Of?
I'm going to be talking about the effect of greenhouse gases, specifically CO2 on the climate, so it's worth taking a moment to look at how much of it makes up the atmosphere. Here is a rough outline of the gases in the atmosphere:
- Nitrogen - ~78%
- Oxygen - ~21%
- Argon - ~1%
- Carbon Dioxide - ~0.038% (as of 19/04/07)
As you can see, the majority is Nitrogen, a mostly non reactive gas. It's interesting that there's so little CO2 though, isn't it? When we talk about changing the concentration of it in the atmosphere, we realise that a little bit can make a large difference, as you'll see further on. So... what is climate change?
The main idea behind climate change is that as the levels of greenhouse gases in the atmosphere increase, the atmosphere retains energy and increases in temperature (on average) due to the greenhouse effect. As the concentration of greenhouse gases increases, the temperature is expected to follow.
How Do We Know It's Not Natural?
We know what the carbon dioxide concentrations have been for the last 400,000 years, and we know roughly what the conditions were at each point (temperature, and such). Take a look at this graph:
So, there are the carbon dioxide concentrations, and corresponding average temperatures for the past 400 000 years, taken from ice core data at Vostok, Russia. I quite like it, personally, because it shows such a good correlation between CO2 and temperature. As CO2 goes up, temperature goes up too. Notice that temperature does tend to lag behind CO2 somewhat, indicating that CO2 rising is the cause of the temperature rising, not the other way round. They're so close, however, that it is hard to be certain.
There's something far more important to note about this graph, though. Notice, that the CO2 concentration has never really exceeded the range 180-~290 ppm (with a spike to 300ppm at one point). In the last 400,000 years, the concentration has stayed in that band.
Just to be clear, ppm stands for "parts per million". 280ppm of CO2 is the equivalent of 0.028% of the atmosphere. Put another way, the amount of CO2 in the atmosphere has never exceeded 0.018-0.030% in the past 400,000 years.
Notice also the difference in temperature between when the CO2 concentration was 180ppm (say at about 140,000 years ago) and when the CO2 concentration was 280ppm or so (shortly thereafter). It's about 12 degrees (roughly -9 to +3). That's what a difference of 100ppm makes.
The plot's about to thicken, let me show you another graph (this time of more recently):
http://maps.grida.no/go/graphic/global_atmospheric_concentration_of_co21
Forgive the slightly tacky buildings and plane! As you can see, just as the industrial revolution started the CO2 concentration was hovering around 280ppm, so within the range of the previous 400,000 years. Then, we happened, and in the space of just over 100 years, the CO2 concentration jumped to 370ppm in 2000 (377.3ppm in 2006), so it's very nearly risen by another 100ppm.
We saw earlier that sometimes the CO2 increase preceded the temperature increase. As such, we're now starting to see global temperatures slowly creeping up.
Conclusion
So, there is it, "What is Global Warming?" answered in a nutshell. Don't believe people who say there's no hard evidence for climate change, and these are just the basics! CO2 concentrations are higher than they've been for the past 400,000 years, and anyone who claims this won't have any effect is being a little naive, I'm afraid. Based on data, the average global temperature is only going to up. The question is, though, by how much?
