In that case I'm wondering if you're in effect making the classic "mistake" of confusing weather and climate. The reason we know that humanity has contributed to Climate Change (as the report I linked says, it is "unequivocal") is because there is a clear signal that dates from the Industrial Revolution, where you can measure the human contribution to a rise in CO2 (and other greenhouse gases, but mainly CO2), above and beyond that which could be accounted for in natural sources. In other words, there's nothing particularly about *this* year that screams "Humans caused this", but rather what screams it is the last few decades.
As an example in a different direction, this year has been, at least compared to the last few, very quiet in the Atlantic Hurricane front. That's been attributed to something called the "Saharan Air Layer", and I won't pretend to know what that means beyond what it says in the wiki page. But, for every one of the last seven years, storms have formed earlier than usual, activity has been higher (often far higher) than usual, and there have been several record-breaking storms, and in general there's been a trend of increasing rates of activity in the region since at least the mid-1990s. It's easy to see why this might be due to Climate Change: hurricanes form more easily over warmer seas, and while it's clearly more complicated than that, it's enough of a hint to tell you that as the world heats up then you'd expect, in general, more hurricanes, and stronger ones at that, to form. One year bucking the trend doesn't change this.
Conversely, of course, one year of particularly extreme heat isn't in itself suggestive of anything. But, again, that's why it's important to consider the longer-term trends. Again, the report I linked notes that average global temperatures have increased by something like one degree as compared to the late 19th Century, and it is "likely" that most of that change has been driven by human activity. As an aside, it's important to note that the report's use of "likely" is based on the weight of evidence gathered over many hundreds of studies conducted by many thousands of scientists over some decades.
Climate sceptics, as a rule, love to point to certain exceptional years as evidence for, or even proof of, humanity's inability to affect the Climate in a meaningful way. They are invariably mistaken to do so. I'd encourage you not to fall into this same trap. As you note, humans have affected the planet in numerous ways dreadfully, and, yes, plastics and the waste they create are one particularly tragic example. Climate Change in general is, sadly, just one more tragedy in a whole pile of tragedies.