A high school student in Ottawa, Jin, writes to ask me for help with a theme on the question of whether global warming is caused by human activities. Here’s my answer:

The simple answer is ‘yes’, global warming is caused by human activities. In fact we’ve known this for over 100 years. Scientists in the 19th Century realized that some gases in the atmosphere help to keep the planet warm by stopping the earth losing heat to outer space, just like a blanket keeps you warm by trapping heat near your body. The most important of these gases is Carbon Dioxide (CO2). If there were no CO2 in the atmosphere, the entire earth would be a frozen ball of ice. Luckily, that CO2 keeps the planet at the temperatures that are suitable for human life. But as we dig up coal and oil and natural gas, and burn them for energy, we increase the amount of CO2 in the atmosphere and hence we increase the temperature of the planet. Now, while scientists have known this since the 19th century, it’s only in the last 30 years that scientists were able to calculate precisely how fast the earth would warm up, and which parts of the planet would be affected the most.

Here are three really good explanations, which might help you for your theme:

  1. NASA’s Climate Kids website:
    It’s probably written for kids younger than you, but has really simple explanations, in case anything isn’t clear.
  2. Climate Change in a Nutshell – a set of short videos that I really like:
  3. The IPCC’s frequently asked question list. The IPCC is the international panel on climate change, whose job is to summarize what scientists know, so that politicians can make good decisions. Their reports can be a bit technical, but have a lot more detail than most other material:

Also, you might find this interesting. It’s a list of successful predictions by climate scientists. One of the best ways we know that science is right about something is that we are able to use our theories to predict what while happen in the future. When those predictions turn out to be correct, it gives us a lot more confidence that the theories are right: http://www.easterbrook.ca/steve/?p=3031

By the way, if you use google to search for information about global warming or climate change, you’ll find lots of confusing information, and different opinions. You might wonder why that is, if scientists are so sure about the causes of climate change. There’s a simple reason. Climate change is a really big problem, one that’s very hard to deal with. Most of our energy supply comes from fossil fuels, in one way or another. To prevent dangerous levels of warming, we have to stop using them. How we do that is hard for many people to think about. We really don’t want to stop using them, because the cheap energy from fossil fuels powers our cars, heats our homes, gives us cheap flights, powers our factories, and so on.

For many people it’s easier to choose not to believe in global warming than it is to think about how we would give up fossil fuels. Unfortunately, our climate doesn’t care what we believe – it’s changing anyway, and the warming is accelerating. Luckily, humans are very intelligent, and good at inventing things. If we can understand the problem, then we should be able to solve it. But it will require people to think clearly about it, and not to fool themselves by wishing the problem away.

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