This is one of many rumors that are known to be untrue, which I still run into online sometimes. It's like one of those emails that's been long-since debunked on snopes.com, but you still see it being forwarded around. Even if Penn & Teller did repeat it on their TV show, or even if Michael Chrichton did put it in one of his books, it hasn't become any more true.
When a statement appears in print, whether in a newspaper or a blog (this one included!), the original source of the information must be checked before accepting it as fact. For example, The New York Times is a very popular newspaper, but it is not a peer-reviewed scientific journal. That means it is not an original source of a scientific finding, it merely reports on them. Media can be susceptible to problems of misrepresentation, misunderstanding, and sometimes perhaps purposefully misreporting on a scientific study in order to attract readers. To determine the scientific conclusion on a subject, reference the original source, which will always be one of the major peer-reviewed scientific journals rather than a popular newspaper or magazine. Newspaper and magazine articles which report on peer-reviewed scientific findings will always cite the original scientific journal as a source, if they want to be considered credible.
In the case of the rumor regarding scientists in the 1970s predicting an ice age, this comes from media reporting rather than science. There were some articles in the 1970s reporting this in the New York Times, one article in Newsweek, and one in Time Magazine. Here are some links to the articles so you can read for yourself where this idea came from:The Newsweek article
You won't find any of the articles quoting actual climatologists predicting a coming ice age. You will find the journalist making conclusions without attributing them to any scientist or scientific publication. Some conclusions in the writing are attributed vaguely to "some scientists" without a specific source. You will also find that the quotes that are given don't specifically relate to the conclusions in the article. This of course is poor scientific reporting. Ironically, the Newsweek article mentions that the average equatorial temperature has been rising rather than falling, and the Time article specifically cites one scientist saying they believe the cooling to be temporary.
But regardless, articles in a newspaper like The New York Times, or magazine articles like in Time or Newsweek are not peer-reviewed scientific journals. In order to find out if there actually was scientific agreement predicting cooling (or even an ice age) in the 1970s, you must go to the actual scientific papers on the subject in the journals.
The research work to do this is actually pretty easy. All scientific journals are archived and indexed for searching.
Also, the rumor about a cooling consensus in the 1970s is such a widespread one, that a survey of the scientific journals has already been done to look into it. Here's the paper, researched by the NOAA National Climatic Data Center, and published by the American Meteorological Institute.
It says that in the period of time between 1965 to 1979, there are a total of 7 peer-reviewed studies that predicted cooling. This is clearly where the media articles were reporting from. However, none of those studies predict an ice age, just cooling. But, that's beside the point, because in that same time period, there are 44 peer-reviewed articles that predict warming driven by CO2 in the atmosphere, rather than cooling. Far more scientists were in agreement, even back in the 70s, about global warming.
If you look at the peer-reviewed scientific literature today, with 40 additional years worth of scientific study looking at the question in far more depth, you will find that scientific agreement is, by now, overwhelming that global warming is occurring and that it is anthropogenic.
You can verify this by reading the history of statements released by the National Academy of Sciences or the American Association for the Advancement of Science on the climate change issue. These are the two most credible scientific organizations I know to exist in the US. Back in the 1970s, the NAS did the most comprehensive study on climate change available back then and concluded this:
"We do not have a good quantitative understanding of our climate machine and what determines its course. Without the fundamental understanding, it does not seem possible to predict climate."
That was their conclusion in the 70s. It's obviously a far cry from there being scientific agreement predicting an ice age, and gives a good indication of how conservative in predictions the true scientific community is, considering that at that time there were already a large majority of peer-reviewed studies predicting warming.
Compare this to the current statement released by NAS:
"There is now strong evidence that significant global warming is occurring. It is likely that most of the warming in recent decades can be attributed to human activities. The scientific understanding of climate change is now sufficiently clear to justify nations taking prompt action."
This same statement was released jointly by the Academies of Science from:
This is why scientists say that the evidence has by now led to overwhelming scientific agreement on this issue among the respected scientific organizations of the world (as opposed to media publications).
Various media outlets report on the current scientific literature differently, often using misleading headlines. Just like the Times article from the 70s, things haven't changed in how media sometimes spins the story. And this causes people lots of confusion as to what the actual studies and scientific conclusions are. But, it's not difficult to go straight to the source of the scientific papers themselves, rather than getting lost in how the media reports it.