Well, can you find me one person in the world who did take her seriously?
Er...there are plenty in this thread, myself included. I'm not sure if you're familiar with the past antics of Ms Crow, but she is no stranger to sticking her neck out and making asinine statements about topics she doesn't appear to have any education about. "Celebrity makes stupid comment" is extremely common. Whilst I thought her suggestion was incredibly thick, it didn't occur to me it was a joke because she says this sort of thing on a regular basis, depending on what political bandwagon she's trying to sell records on the back of.
So yes, me and everyone else in this thread, plus the BBC and the thousands of other people who reported this seriously, and the millions who read it, were had. But there's no pride or triumph for her in that because the joke is neither sophisticated nor funny. If she wasn't on an environmental campaign, then it would have been immediately suspect, but given the context and her history of bleating about war, karma, oil, Saddam Hussein, WOMD, CTs, and now the environment, I can fully understand why people thought "god, another stupid statement from a bored millionaire".
If you go on a bus tour called STOP GLOBAL WARMING, then make suggestions about how to stop global warming that you don't actually want people to take seriously, then you deserve ridicule. You'd think they'd be able to afford a PR agent, because this will do more to damage their 'message' than any number of serious statements.
Mocking your own message? Come on. That's an error of judgement. Presumably we're now supposed to assume that anything Sheryl Crow says is not to be taken seriously? That will be problematic when she suggests that people stop driving SUVs.