It has not been discredited. Ultimately it is unknown what would happen since atmospheric testing was banned over half a century ago. However, I find it hard to believe that a thermonuclear war would not produce a very significant amount of atmospheric particles. The amount of cooling may be over- or under-stated, we really don't know, but there is probably some effect.

Which has constantly made me wonder why we haven't experimented with it as a means of cooling the average global temperature.

We need a staging/QA Earth so we can run these kinds of experiments.

Selenium isn't the best fissile material :p

Because it doesn't cool the global temperatures by virtue of being itself. Nuclear winter is caused when massive amounts of debris and other particles (like smoke) are shot up into the air, blocking some of the sunlight, resulting in cooler temperatures. This also has the affect of less crop yields due to reductions in sunlight, less electricity generated from solar panels, and other consequences. So unless we want to voluntarily eat significantly less and use less energy in the name of cooling Earth's temp for 5 years, it's not a very viable alternative.

Source: https://en.wikipedia.org/wiki/Nuclear_winter#Mechanism

Filling the sky with radioactive particles to combat global warming is an end I hope we never reach.

Assuming low-radiation devices can be used, if things get dire then it certainly beats the alternatives.

It one of those things we don't want to experiment with to find out. Interestingly, the burning of fossil fuels is arguably an uncontrolled climate change experiment that might lead to thermohaline disturbances, an Ice Age and/or hypercanes.

I have a feeling its the same as pouring a few bottles of poison in a swimming pool. We just have so much atmosphere.. sure, there will be a minimal but significant drop in temperature and some plants may not grow as abundantly as normal, but globally, the consequences are not (as) cataclysmic.

Edit: apparently people do not know how vast the amount of water that goes in a typical swimming pool is..

People at HN are typically analytical thinkers who appreciate fact over conjecture. Your post starts with “I have a feeling.”

And any analytical mind can take some educated guesses and say 'well, if I pour 6L of a poison in an average public swimming pool of 30x2x10m, that's 1 part poison per 100.000 parts water, or 0,00001% poison. Same goes for the atmosphere and blasted up particles. Aside from that, most people would read'I feel like' ~= 'I guesstimate', but it seems these days some of us need explicitness past the normal verbal conventions.