We've been geoengineering climate for decades.
In depth article on the subject.
For decades humans have been emitting carbon dioxide into the atmosphere, creating a greenhouse effect and leading to an acceleration of the earth's warming.
At the same time, humans have been emitting sulphur dioxide, a pollutant found in shipping fuel that has been responsible for acid rain. Regulations imposed in 2020 by the United Nations’ International Maritime Organization have cut ships’ sulfur pollution by more than 80% and improved air quality worldwide.
Three years after the regulation was imposed, scientists are realizing that sulphur dioxide has a sunscreen effect on the atmosphere, and by removing it from shipping fuel we have inadvertently removed this sunscreen, leading to an acceleration in temperature in the regions where global shipping operates the most: the North Atlantic and the North Pacific.
We've been accidentally geoengineering the earth's climate, and the mid to long term consequences of removing those emissions are yet to be seen. At the same time, this accident is making scientists realize that with not much effort we can geoengineer the earth and reduce the effect of greenhouse gas emissions.