Ed Berry writes (letter, May 22) that he believes that nature is responsible for climate change and that because humans generate "only 4%" of the CO2 that flows into the atmosphere, "simple physics and common sense" say that human-generated CO2 can't possibly affect the world's climate.
Here is some simple physics and common sense. Lets say we have a see-saw — basically a balance beam. Let's put a one-ton weight (32,000 ounces) on each end. I think we can agree that it will sit there — balanced. A little kid comes by and drops a package of gum that weighs 4 ounces on one end. What happens? The now heavier end will fall until it hits the ground.
The atmosphere has generally been in balance for a very long time. Humans have put their thumb on the scale.
If you'd be open to reading a fairly concise, scientifically accurate description of the matter, please take a look at http://www.skepticalscience.com/human-co2-smaller-than-natural-emissions.htm