What is the expected specific, immediate, local effect of that? Can you tell a particular person (the abovementioned Midwest farmer) some particular clear consequence of phytoplankton decline he's going to personally experience in his lifetime (say, 2070) or the lifetime of his kids (say, 2100) if he doesn't do the utmost to prevent climate change change ?

The articles you quoted make no really scary (to the target audience) claims whatsoever. The third includes an expected impact on agriculture (https://journals.plos.org/plosbiology/article/figure/image?d...) which shows neutral or even positive effects on agriculture in much of first world (and horrible effects on Brasil and SE Asia, but that's not relevant to the USA consumer whom we're asking to change habits).