In Blade Runner 2049 (2017) it is set in California, but is seeming always raining or overcast, almost more like Seattle climate. It clearly does not match the climate of California as we know it. I assume there is some kind of in-universe explanation for this but I don't recall it being explicitly mentioned in the movie. What happened to the Earth's climate in the Blade Runner universe?
We don't precisely know .
Only that...it seems to be environmental related...and probably our own fault.
In one of his earliest interviews about the movie, Villeneuve teased that the world will be on the brink of environmental disaster in the film. “The climate has gone berserk — the ocean, the rain, the snow is all toxic,” he said.
In the original “Blade Runner,” Ford’s Deckard was constantly soaked by rain, but in the new film, the weather is much less predictable. In the intervening years, the climate has gone berserk due to rampant pollution, turning Los Angeles into a chilly, desolate place. “As much as the first movie had an atmosphere of constant rain, in this one it would be colder,” the director says. “Basically, you could say that the first movie was made by a man from London, England, and the second one was made by someone from Montreal, Canada.”
In the very beginning where they give a brief textual exposition of the world it's stated that:
After the collapse of eco-systems in 2020's humanity was on a brink of a great famine, but Wallace's genetically engineered products saved humanity.
Apparently the eco-systems collapsed not only locally on the West Coast but throughout the whole world which could lead to big changes in the climate since a lot of climate affecting parameters are dependant on the products of living organisms. Also consider that in the original movie Los Angeles already looked more like New York than California which means that the climate has been changing in this universe for quite some time.
Also in 2022 a nuclear warhead was detonated producing immense EMP which effects are still resonating in 2049. Maybe the warhead dealt more than EMP damage?
The climate is already bleak in 2019 and gets worse as time progresses, which is even more aggravated by the nuclear explosion above LA's airspace in 2022. But the erratic weather, violent sea and walls we see in 2049 are mainly due to the effects of man-caused climate change.
From the oficial movie website:
2049: When we return to Los Angeles, 30 years after the original movie, climate change has caused the sea level to rise dramatically. A massive Sea Wall has been built along the Sepulveda Pass to protect the Los Angeles basin