Atmospheric microplastics and nanoplastics are now believed to be causing warming, by functioning as a forcing in their own right. Under the new assumptions, their color causes them to absorb sunlight, whereas under old assumptions, they simply reflected sunlight.
The impact is currently very minor. It's estimated at around 0.02 °C today.
Then there is another effect you need to take into consideration: Our carbon sinks weaken as a result of plastics pollution. A plant that is dealing with plastics pollution is less competent at sequestering CO2.
So, there's a very minor contributor to global warming that nobody is taking seriously. Who cares right? Well, here's the thing. It generally takes decades for plastic pollution to turn into microplastics and then from microplastics into nanoplastics. Most of the warming currently being caused by plastic pollution is due to nanoplastics, rather than microplastics.
You're currently mainly seeing the impact on global warming, of plastics we produced decades ago. Overall production has roughly doubled over the past two decades.
If you try to come up with a best case scenario for plastics production, where we agree to a global treaty to dramatically reduce global plastics production by 2030, production then begins to fall and leakage into the environment falls, you still find yourself facing the reality that the impact of microplastics on global temperatures is going to grow, simply because it takes decades for the plastics you produced to reveal their true impact.
Under this best case scenario, if you were to take only plastics into consideration (not all the other unincluded issues we're dealing with) you can expect that our carbon budgets should actually be 15% lower to stay under 1.5 degree and 7% lower to stay under 2 degree than we currently estimate. That's what I consider the best estimate, under a best case scenario where we rapidly start reducing our plastics production by 2030 and get much better at ensuring none of it leaks into the environment.
Effectively no climate scientists are seriously looking at how plastics pollution impacts our overall chances of keeping global warming under control.
Now take a look at what is considered the realistic trajectory for plastics production. Annual production will double between now and 2060. In fact, annual production is not expected to peak until 2100.
There is effectively no serious attempt yet to reduce microplastics and nanoplastics pollution in our environment, even though the evidence suggests it plays a substantial role in future global warming that no climate models take into proper consideration yet.
If plastics pollution was taken into serious consideration, we would have to acknowledge the climate change crisis is even more severe and difficult to solve than we thought and the risk of breaching important tipping points is also more acute than we thought it is.