Al and Tipper Gore announced today that they were separating after 40 years of marriage.

The announcement came in the form of an e-mail message. Friends described the decision as mutual.

“We are announcing today that after a great deal of thought we have decided to separate,” the couple said. “This is very much a mutual and mutually supportive decision that we have made together, following a process of long and careful consideration. We ask for respect for our privacy and that of our family, and we do not intend to comment further.”

The existence of the e-mail message was first reported by Politico. A spokeswoman for Mr. Gore, Kalee Kreider, confirmed its authenticity.

There is a global warming joke here someplace. Any ideas?