This is a singularly unhelpful term in the context. It is clearly intended to resonate with the term "Holocaust denier", but we are dealing with a very different phenomenon here. The Holocaust is a historical fact, attested to by thousands of reliable witnesses who survived Hitler's death camps, the testimony of Allied forces who liberated them, the confessions of camp guards, and numerous Nazi historical documents. Those who deny that it occurred are either deluded loonies, or more commonly evil racists seeking to whitewash the reputation of the Nazi regime.
Climate change is not a solid fact in this sense. It is an interpretation of masses of statistical observations, which means that more than one interpretation is possible. The majority of climatologists concur on it, but those who do not are better described as sceptics than deniers. In fact there are several levels of interpretation at work:
- Climate change is occurring, i.e. substantial long term change in prevailing patterns of temperature, precipitation and wind strength and direction, as opposed to periodic shorter term fluctuations in local weather patterns. Most scientists agree that we are now seeing long term global warming, though some diagree, and some even posit the opposite - global cooling.
- Given that global warming is occurring, human activity is responsible for (or a major contributor to) it. Again the scientific consensus agrees with this interpretation, but again there are dissenters. The general view is that the rise in the emission of greenhouse gases, particularly carbon dioxide, is a key factor in causing rising temperatures.
- This warming is having, or will have, a disastrous effect on humans and the many other creatures with which they share the planet.
- Given this, we should change our behaviour to mitigate the effects. Here we begin to move from scientific to moral and political questions. Some prominent voices have suggested that we should just "get used to the idea" - not a view, I suspect, that will be shared by people in countries such as Bangladesh and the Maldives, or cities like New Orleans, which could largely vanish with a rise of a few feet in sea level.
What does this mean for proposition 4? In my view, regardless of the fact that climate change may eventually be disproved, we should continue to act for now as if it is a proven fact. If it turns out to be a false alarm, we will have at least cleaned up much of our atmospheric pollution and developed new cleaner sources of energy, while doing no harm. If not, our actions now may make the difference betwen the survival and extinction of the human race.