An argument that I often encounter is that uncertainties in climate science shouldn’t be publicly emphasized since that will make it harder to inspire action on proposed climate policies. It is thought that publicly highlighting a lack of knowledge/understanding on some aspect of the science provides ammunition to anthropogenic climate change skeptics and thus should be avoided.

I agree that highlighting scientific uncertainty in isolation is misleading because it fails to convey that scientists are very certain about a lot of fundamentals. However, I believe that being honest about uncertainty, and yes even highlighting it, is precisely what builds the credibility that is necessary for the public to trust science in the first place.

As an example, which string of statements (A or B) inspires more trust/credibility?

A:
A.1 The Earth has a greenhouse effect that keeps it warmer than it would be otherwise
A.2 Humans are burning fossil fuels that increase greenhouse gas concentrations
A.3 These increasing greenhouse gas concentrations are warming the planet
A.4 This warming is likely to increase stress on crops at low latitudes
A.5 Assuming current agricultural practices, this could have a substantial detrimental impact on crop prices and/or food availability in the future but crop and economic models have many known problems and are inherently uncertain

or

B:
B.1 The Earth has a greenhouse effect that keeps it warmer than it would be otherwise
B.2 Humans are burning fossil fuels that increase greenhouse gas concentrations
B.3 These increasing greenhouse gas concentrations are warming the planet dramatically
B.4 This warming will cause global crop failures and food shortages in as little as a decade or two
B.5 These food shortages will create millions of climate refugees that will destabilize the global social/political order

Clearly, A sounds more credible and it is also much more scientifically justifiable. However, I often see climate-action activists preferring to use narratives much more along the lines of B. The argument goes that people need salient, specific, alarming examples in order to get them to pay attention to the issue.

That may be the case, but I would argue that any extra attention that is garnered by using B is more than offset by the risk of losing credibility.

What happens when a dramatic prediction like B.5 does not come true? In the mind of the public, the credibility underpinning the entire chain (B.1, B.2, B.3, and B.4) is undercut. If on the other hand, uncertainty is emphasized where it is appropriate (A), the entire chain is not as vulnerable to being dismissed. In other words, concerns about crops may not materialize as envisioned (A.4 and A.5) but that wouldn’t undermine A.1, A.2 and A.3.

Anthropogenic climate change skeptics distrust scientific conclusions about climate change at least partially because they contend that uncertainties are being underemphasized. Thus, true ‘ammunition’ for anthropogenic climate change skeptics comes from deemphasizing, rather than emphasizing uncertainty.