Our friend the “skeptic,” Michael Shermer wrote a book review in Nature about ignorance that, despite his bravado about scientific certainty, reveals more ignorance than knowledge.
Knowledge and ignorance can be divided into four quadrants: what we know we know, what we know that we know not, what we know not that we know, and what we know not that we know not. The last two, being unknowns, collapse into one category of ignorance. This is an expansion of Donald Rumsfeld’s triad of known knowns, known unknowns and unknown unknowns. Shermer uses an anecdote from a 2002 Rumsfeld speech to open his review of Ignorance: How it Drives Science, by Stuart Firestein (Oxford, 2012).

It is this last category that is the focus of Stuart Firestein’s sparkling and innovative look at ignorance, and how it drives the scientific process. Firestein is a neurobiologist at Columbia University in New York, where he teaches a wildly popular course on ignorance, inviting scientists to tell students not what they know, but what they don’t. He muses, would you rather earn an A or an F in a class called Ignorance?

Shermer first admits that science has its limitations, contrary to simplistic public perceptions of its progressive infallibility:

In reality, as mathematician Andrew Wiles says in the book, science consists of “groping and probing and poking, and some bumbling and bungling.” A switch is discovered and a light comes on. It is like looking for the proverbial black cat in a dark room.
It is in the dark that cutting-edge science takes place. To make discoveries, researchers need to look beyond the facts — to where they run out, says Firestein. Scientists should “forget the answers, work on the questions.” That is good advice, because the mountain of facts is now so vast that we cannot hope to learn, let alone remember, them.

But later, Shermer confidently states the possibility of scientific progress:

To Rumsfeld’s categories, Firestein adds one more: unknowable unknowns, or “things that we cannot know due to some inherent and implacable limitation.” He puts history in this category, but I would not. When history is defined as anything that happened before the present, it includes much of astronomy, geology, archaeology, paleontology and evolutionary biology — fields with hypotheses that can be tested with as much rigor as experiments in the lab.

Yet if one does not know the extent of the unknowable unknowns, let alone the unknown unknowns, there is no way to measure progress. Shermer attempts to rescue scientific progress with an argument from analogy:

We should remember that when a sphere becomes bigger, the surface area grows. Thus, as the sphere of scientific knowledge increases, so does the surface area of the unknown. Firestein’s book reminds us that it is at this interface that we can claim true and objective progress.

The analogy seems contrived. It is just as conceivable to invert the ratio, and assert that ignorance grows as the volume, not the surface area. Shermer himself admits as much earlier in his review, “the mountain of facts is now so vast that we cannot hope to learn, let alone remember, them.” That implies that ignorance includes forgetfulness of what we thought we knew. Factor in the reminders from historians of science that yesterday’s scientific facts often become today’s myths, and the possibility for exponential expansion of ignorance becomes daunting. How does he know our knowledge is not like a marble in a boxcar? or a galaxy?
Shermer has a reason for clinging to scientific triumphalism. Anything less would cede ground to his opponents, the skeptics of his skepticism:

I worry, too, that too much emphasis on ignorance opens the door to creationists, climate deniers and others with political agendas who wish to challenge mainstream scientists. Acknowledging our ignorance is good, but we should also recognize the well-supported theories that science has confidently given us.

Now we see that Shermer’s unknowns include ignorance of his own denialism (of intelligent design), his own political agenda, and the reliability of “mainstream scientists.” Furthermore, he seems ignorant of the shaky ground that supports some of those “well-supported theories” that he admires so much (like Darwinism), and “that science has confidently given us,” ideas that could well fall in a spectacular collapse in the foreseeable future.
In short, Shermer has chosen to assert knowledge that he does not have, because he cannot establish that his confidence is outside of unknown unknowns or unknowable unknowns. Being a philosopher at some level, Shermer should know better. Ignorance is unavoidable and forgivable unless it is willful.