Here's the thing:
The earth is fucking massive.
There are lots of things on this fucking massive earth. More than you can comprehend.
Therefore there are shittonnes of variables, and it's difficult to tell what happens when we change a variable.
Changing a variable could lead to a predictable result in one place, and a less predictable result in another. One of a million examples: if you increase the albido of the earth (so the earth reflects more sunlight, volcanoes do this well) you will decrease its temperature, but this could cause an ocean current to change making it colder in certain areas of the planet. Example is the UK: an island on the same latitude as upper British Colombia and Siberia, gets none of the cold because of Atlantic sea currents push the jet stream north.
Because of this, if we are to determine any real correlation we need an imperial megafucktonne of data.
When it comes to correlating human produced carbon dioxide and global average temperature, we have so much fucking data we can say there is a very strong positive correlation.
When it comes to determining the effects of global warming we are less certain.
Warming the planet will not be even. Some parts will warm more than others. Some parts may get colder. Yes, some parts may see harsher winters than they did when the earth was cooler.
Current models can't really predict exactly what will happen if/when the earth continues to warm, but they mostly agree that we will see more extreme weather. That's more droughts, harsher monsoons, hurricanes, tornadoes, snowstorms.
Tl,dr: global warming is happening but any predictions about climate change are guesswork.