David Friedman, who we can safely assume has a better sense of the late Milton Friedman’s thoughts and beliefs than most people, disagrees with a recent Forbes article asking WWMFD:
A recent Forbes article is headlined “What Would Milton Friedman Do About Climate Change? Tax Carbon.” It reports on a forum at the University of Chicago at which several economists, including Michael Greenstone, described as the “Milton Friedman Professor of Economics at the University of Chicago,” argued that Friedman would have supported a carbon tax. The evidence for that claim was a 1979 clip from the Phil Donahue show where Milton Friedman argued that if the government is going to do something about emissions, they should use an effluent tax rather than direct regulation. He does not actually say that government should do something about emissions, only that there is a case for doing so and, if it is done, the best way to do it is by a tax on emissions.
To get from there to the conclusion that he would have favored a carbon tax requires at least one further step, a reason to think that he would have believed that global warming due to CO2 emissions produced net negative externalities large enough to justify doing something about them. The problem with that claim is that warming can be expected to produce both negative externalities such as sea level rise and hotter summers and positive ones such as longer growing seasons and milder winters. The effects will be spread out over a long and uncertain future, making their size difficult to estimate. My own conclusion, defended in past posts here (one example), is that the uncertainties are large enough so that one cannot sign the sum, cannot say whether the net effect will be positive or negative.
I do not know if my father would have agreed but I have at least a little evidence on the subject, more than offered in the Forbes article. The same issue arose in the earlier controversy over population. Just as it is now routinely assumed that warming is bad, it was then routinely assumed that population increase was bad. Forty years ago I wrote a piece on the subject for the Population Council in which I attempted to estimate the externalities associated with population. I concluded that they were too uncertain for me to tell whether the net effect was good or bad. My father read the piece and commented on it. If he had disagreed he would have said so, and he did not. It is possible that he would have felt differently in the case of climate change, but I can see no reason to expect it.