I think the only thing I know that can drop down temperature to the planet is a mega volcanic eruption,
[The 1815 eruption of Mount Tambora, Indonesia, the Laregest eruption in recorded history, ejected an estemated 150 cubic kilometers (36 cubic miles) of debris into the air. The average gloval temperature cooled by as much as 3 Celsius (5.4 Fahrenheit), causing extreme weater around the world for a period of three years. As a result of Mount Tambora's Voclanic Ash, North America and Europe Expeirenced the "Year without a Summer" in 1816. This year was characterized by widespread crop failure, deadly famine, and disease.]
-Taken from a scientific study.
Look up Yellowstone Mega volcano eruption if you're into Apocalyptic scenarios that would be just as bad for the human civilization as climate change will be; however, it would probably be a better outcome for overall life on the planet.