Marx did not have the benefit of the concept of externalities for his economic work. If he had, Marx would no doubt have documented the externalities of slavery in his correspondence during the American Civil War, given that correspondence was forensic in its detail about how “the slaveholder party” captured American government from its founding. (read much of that work here)
Let’s refresh on the concept of “externalities”—
A negative externality is any difference between the private cost of an action or decision to an economic agent and the social cost. In simple terms, a negative externality is anything that causes an indirect cost to individuals. An example is the toxic gases that are released from industries or mines, these gases cause harm to individuals within the surrounding area and have to bear a cost (indirect cost) to get rid of that harm. Conversely, a positive externality is any difference between the private benefit of an action or decision to an economic agent and the social benefit. A positive externality is anything that causes an indirect benefit to individuals. For example, planting trees makes individuals' property look nicer and it also cleans the surrounding areas.
In the 21st century, America still bears the burden of the externalities of slavery. Economically, slavery was nothing more than unpaid involuntary labor, the private costs of which were never paid, but instead entirely borne by the public. These externalities extended from the individual slave unpaid for his/her labor (and the associated cost borne by him/her), all the way to today’s societal costs. The cost of this labor has never been paid, ever, (see the reparations debate), thus, the externalities remain.
The immensity of slavery’s externalities lie not only in its duration — the entire history of the United States, with no end in sight. Perpetuating capital’s control over American government to protect profit from unpaid involuntary labor necessitated the division of labor, one against the other, by race. The basic human instinct of fear of some “other”, be it by color, or religion, or immigrant status, is essential to paralyze politics, rendering government impotent to address any problem resulting from market dynamics. Thus, the never ending con game that there is always some race inferior to your own to bear the worst burdens. Marx predicted this con game in his Nov. 7, 1861 article in Die Presse, when he analyzed what would happen to America should the Confederacy be allowed to secede.
“…the white working class would gradually be forced down to the level of helotry. This would fully accord with the loudly proclaimed principle that only certain races are capable of freedom, and as the actual labor is the lot of the Negro in the South, so in the North it is the lot of the German or Irishman, or their direct descendants.”
Climate change externalities are equally as immense — stretching as far as the eye can see, with no end. Paralyzing the state against the market in favor of climate change also relies on precisely the same division of the populace required to perpetuate slavery. The only functional economic difference between slavery and climate change is where the societal burden of the unpaid cost lands — not just on society, but the planet itself. Slavery’s externalities burned America nearly to a burnt ember from 1861-1865. Climate change’s externalities are, this moment, burning the planet to an ember.
Seen through the lens of Marx’s Civil War analysis, the fossil fuel industry, and its various tendrils controlling American government for their own profit based in unborn private cost instead borne by the public, is functionally no different from the slaveholding aristocracy of the Confederacy. For the most comprehensive collection of Marx & Engels’ Civil War correspondence, pick up Andrew Zimmerman’s 2016 volume, The American Civil War, Karl Marx & Freidrich Engels.