A combination of things. Natural causes from solar energy, volcanic eruptions, ocean-atmospheric exchange, and yes, burning of fossil fuels. I don't deny that we are experiencing a climate shift. I don't deny that burning fossil fuels is a contributing factor. I just don't think that any of the four things I listed are happening at a level, either individually or in concert with each other, that will take us to some cataclysmic event. Can that change? Yes? Should we be making an effort to control our participation in the process? Yes, and we are. Is it a cause for concern? Yes. Should we be in a state of panic. IMO, no, not at this time. Any evidence that I see has me concluding that the path we were on 30 years ago is leveling out.
BTW, the real solution to carbon emissions is not solar and wind. It's nuclear. Tremendous advances have been made in how it's processed and more importantly, reduction in contamination and waste. If we could get our energy policy to be based upon actual science and not a hyperventilated movie from 1979 we could get ahead of this.