Specific predictions, i.e. future weather reports for specific parts of the planet--are far more complex and difficult. To precisely predict the impacts of human-caused climate change, you're combining all the reasons it's hard to predict the weather with all the reasons it's hard to predict the stock market and politics.
But that doesn't mean it's not happening. I can start a fire in your kitchen and challenge you precisely predict the patterns in the smoke at 10-second intervals with a resolution of 10 cm; you won't be able to. But we both know that your kitchen will be full of smoke after a while.