Why is the number 350 so important?

According 350.org :

There are three numbers you need to really understand global warming, 275, 390, and 350.

For all of human history until about 200 years ago, our atmosphere contained 275 parts per million of carbon dioxide. Parts per million is simply a way of measuring the concentration of different gases, and means the ratio of the number of carbon dioxide molecules per million other molecules in the atmosphere. 275 ppm CO2 is a useful amount—without some CO2 and other greenhouse gases that trap heat in our atmosphere, our planet would be too cold for humans to inhabit.

Beginning in the 18th century, humans began to burn coal and gas and oil to produce energy and goods. The amount of carbon in the atmosphere began to rise, at first slowly and now more quickly. Many of the activities we do every day like turning the lights on, cooking food, or heating or cooling our homes rely on energy sources like coal and oil that emit carbon dioxide and other heat-trapping gases into the atmosphere. We’re taking millions of years worth of carbon, stored beneath the earth as fossil fuels, and releasing it into the atmosphere.By now—and this is the second number—the planet has 390 parts per million CO2 – and this number is rising by about 2 parts per million every year.

Scientists are now saying that’s too much – that number is higher than any time seen in the recorded history of our planet – and we’re already beginning to see disastrous impacts on people and places all over the world…  Propelled by the news of these accelerating impacts, some of the world’s leading climate scientists have now revised the highest safe level of CO2 to 350 parts per million. That’s the last number you need to know, and the most important. It’s the safety zone for planet earth.

So what should you do?  How can you “fix” the problem of climate change or global warming single-handedly?  Can you really make a difference? 

Turns out, you can.

See Also : An Inconvenient Truth