I believe one useful tactic in challenging nihilists is to zone in on the problem. Many nihilists I've engaged with rely in whole or in part on ruling class Malthusian narratives of overpopulation, individual consumption/impact, etc.

As socialists we are aware of how assiduosly this narrative has creeped into the American conscience, aided materially by millions in ad campaigns by the likes of ExxonMobil to push the responsibility onto consumers. Why is that done? To distract from their astronomical impact on the world.

Once you get nihilists to admit that it is only 100-200 corporations, as well as the profit motive at large that are creating the majority of human led climate change, it becomes easier to convince folks that the problem is indeed solvable. Then you point them towards political power, which will of course allow them avenues and a shared future that addresses all the contradictions we face: privatized accumulation of profit with socialized label, mass inequality, monopoly capitalism/imperialism and its influence on production and consumption, settler colonialism, etc.

Just my two cents, every nihilist is different, we must figure out what misconceptions they hold, in order to address them and bring them into a more revolutionary optimist position.