PET bottles are made by the billions each year, to be precise, 583,3 billion, that is 583.300.000.000 bottles which is an insane number, given the world population is only ~7 Billion people (so maybe wrong?)!
Let’s say its half that, so 300 billion bottles. We can make something else from that PET plastic, namely reflective sheets. If we assume the same thickness we can make the same surface area as those bottles. Taking one bottle as 15 cm diameter, 40 cm high, this is .32 m2 of surface, like a common sidewalk pavement tile. If we multiply this we find we have 96.000 square kilometers of surface.
We can make PET 94% reflective. At the equator the Sun power is 1000 Watt per m2, so this material reflects back 94% of it, which is 940 Watt/m2. For the 96.000 square kilometers this is 9,024 x 10 with 13 zeros, or 90.240.000.000.000 or 90,24 TeraJoule of energy.
The world recieves about 3 400 000 EtaJoule per year, an EtaJoule is 1 with 18 zeros, so 6 more than a TeraJoule. This really is a lot, so the energy send back to space by the reflector may not do much, but it may compensate the loss of sea ice, and it may be used in ways that amplifies its own effect, for instance in mountains, where the colder air then causes snowfall which then cause more white surface to form.
If you reflect 94% of the light back in a region, it will seem like the sun is 94% dimmer there. It will become cold, and rain will fall and probably freeze, I yet have to get a good model to simulate those effects. The wind over the area will also cool down.
If the PET is used on the ocean, preferbly a quiet part of it, then the albedo gain will be quite pronounced. Land Albedo (reflectance) is ~30%, but ocean albedo is near Zero! The water will still be able to radiate heat because the PET will take on the same temperature and will be quite thin. So floating PET on the ocean can help cool it, and the air at the same time.
This kind of idea seems idiotic, but if you consider you can keep oceans alive, seacreatues alive, cool the atmosphere, prevent violent storms (because there will be no evaporation) the advantages start to add up.
Maybe we can stop using PET bottles and cool regions enough so we dont need bottled water anymore!