Currently, most climate scientists agree that 350 ppm (parts per million) of CO₂ (carbon dioxide) in the atmosphere is a safe amount - that is, the amount of carbon dioxide that can be in the air without having irreversible effects on the environment. As of now, the measure is 385 ppm.

Carbon dioxide is a greenhouse gas. As sunlight reflected by the earth goes back into the atmosphere, carbon dioxide and other gases -- such as methane -- prevent the sunlight from going back into outer space, keeping it on the planet. This causes temperatures to go up, which adversely effects weather and the ice caps worldwide. So how much carbon dioxide is in the atmosphere is directly related to the effects of Global Warming. Which is why the amount of CO₂ in the atmosphere must be lowered. Soon.

On October 24th, 2009, thousands of people gathered in locations around the world to take pictures of them, either holding 350 signs or in a 350 formation. You can look at all of the pictures here, on flickr.

It shows that we are not alone in wanting a better environment.

On Friday October 23, the environmental club hosted its own 350 event. During the third lunch block, students from LS formed a very large 350. Chalk lines were drawn on the ground so they would know where to stand. After everyone was in place, photographers took a picture of it. They were high up, of course!

You can see the picture right here.