Put simply, science is the pursuit of objective truth and proceeds under the assumption that there is an objective universe external to the human mind. Scientific inquiry is driven mostly by innate curiosity about how nature works; most scientists I know genuinely love what they do and are in it for discovery.
Sometimes, progress begins with an observation that does not fit within the existing scientific framework. Scientists then try to repeat and improve on the observation to determine whether it really is an outlier. Next, they may pose one or more hypotheses to explain the observation, and if a hypothesis succeeds in explaining not only that observation but others as well, and especially if it successfully predicts what has not yet been observed, the hypothesis may advance to the status of a theory. In science, theory pertains to a principle or set of principles that have been convincingly well established. Thus it is usually not reasonable to say that something is “just a theory” in the realm of science. (However, it may not be unreasonable to say that some idea is “just a hypothesis.”) If the theory of general relativity were “just a theory,” no one’s GPS would work.
Scientists rarely refer to “facts” or speak about anything being settled. We are by our very nature skeptical, and a good way for a young scientist to advance is to overturn or significantly modify a generally accepted principle. But wellaccepted theories are rarely rejected outright; they are much more likely to be subtly modified. For example, Newton’s law of motion was not really overturned by Einstein’s theory of relativity; it was modified to be even more precise.
In climate science, the word skeptic was hijacked some time ago by the media and certain political groups to denote someone who, far from being skeptical, is quite sure that we face no substantial risks from climate change.
The vast majority of climate scientists, as well as all scientists, are truly skeptical. Science is a deeply conservative enterprise: we hold high bars for reproducibility of observations and experiments, and for detecting signals against a noisy background. Most of us are careful to quantify uncertainty as a matter of intellectual honesty. For example, when a meteorologist says there is a 70% chance of rain tomorrow, that probability is not pulled out of a hat but rather is based on a slew of objective guidance. Cynics often use forecast uncertainty to claim that forecasters do not know what they are talking about, but most of us accept it as an honest appraisal of the degree of uncertainty. In science, uncertainty must never be confused with ignorance.
Lastly, being conservative about risk is quite different from being conservative about accepting theories and observations. An incautious person will bet on the high probability that his or her house will not burn down. A conservative person buys insurance. Risk assessment is also a science, and the economics of risk demand that we convolve the probability of something happening with its cost to arrive at a true portrait of the risk.