Though the fact of climate change has not been under scientific debate for decades, the uncertainty of climate change remains. How can this be? How can fact exist so easily with uncertainty? "It simply can't" is the answer given by politicians, political pundits, and others who seek to cast doubt on climate sciences. Especially after the so-called "Climategate" in which climate scientists' emails were leaked to the public and then distorted to show wrong-doing where none existed, the public may be more confused than ever about how fact and uncertainty can coexist.
In scientific circles, "uncertainty" means something different than it does to the rest of us. If I say I am uncertain if I'll go to the store today, it means I may or may not go. When a climate scientist says the sea will rise 0.5 to 1.0 meters in the next 50 to 100 years, it means the sea level is going to rise. The uncertainty is how much it will rise, when exactly it will reach which levels, and where exactly it will rise most (remember the sea is not rising evenly around the world). Scientists are sure about climate change; the questions of uncertainty are the specifics of climate change - how bad will it be in which year, in which place, given a vast array of possible circumstances?
The computer models that calculate climate projections are getting better every year, though each has different strengths and weaknesses, and all of them take a very long time and a lot of processor power to generate. Reports like the IPCC compile multiple models to generate a range of projections - somewhere between the best-case and worst-case scenarios. What are some factors they just can't predict even with these computer models? Most important are the human factors - what are we as a species going to do to address climate change? Will we cut all emissions? Will we do nothing? Will we increase our CO2 pollution?
Scientists are used to dealing with uncertainty. No single study ever "proves" anything; it only points to an answer. When hundreds or thousands of studies point to the same answer, scientists can feel pretty comfortable saying "this is probably the case." They keep that word "probably" because new theories, new technology, or new scientists may discover something that changes everything. Science is never "proof." At best, it is "our best understanding of the way things are." Scientists are rarely comfortable giving a definitive answer. They are comfortable with "best understandings" because there is always uncertainty.
But people are often not so good with uncertainty. Even scientists in their daily non-work-related lives will crave stability. Part of human psychology is that we expect our lives to be today more or less like they were yesterday. We expect the people we know to have stable personalities. We feel great stress when our lives change abruptly. Conservation of Resources theory explains that people work hard to obtain and maintain those things we value most. When the stability of our resources is threatened (much less interrupted), people experience stress that can even become severe enough to affect our health.
It is no wonder that people want to have exact answers about what is going to happen with climate change. And it is no wonder that those who have an anti-climate-sciences agenda are able to exploit our very real need for answers when they claim scientists don't really know anything or are just making it all up. But with nearly 7 billion people on the planet, almost 200 countries, and certainly more than one opinion on what to do about climate change, it is no wonder that there is so much uncertainty about what the future holds.