What is the latest information on the increase in carbon dioxide in the atmosphe

Dear Tom,
What is the latest information on the increase in carbon dioxide in the atmosphere?

— Leon Danileff, Norfolk, Neb.

Dear Leon,

A recent report from researchers at the University of Southampton in the United Kingdom says that unless greenhouse gas emissions are reduced, the concentration of carbon dioxide in the atmosphere (one of the primary “greenhouse gases”) will rise to 900 parts per million by 2100. If emissions remain unchecked until 2400, the concentration could rise to 5,000 parts per million. Such an increase would result in global temperatures higher than anything seen in the past 420 million years.

Such predictions are certainly not flawless because they are based on many factors, some of whose effects are still unknown. However, the study’s lead author, Gavin Foster, said, “just as far as we know … the [warming] in the future is going to be