More cautious scientific studies say it's about 50-50 between human activity and natural processes. But some scientists claim it is 100% caused by human activity. So the actual reality is likely to be somewhere between 50% and 100%. Whatever the exact value, it's clear human activity is the dominant driving factor.
More worryingly, an increasing number of climate scientists are now saying we may have already passed the tipping point where nothing we do will fully rectify the situation. This doesn't mean we should just give up, but it does mean we have to factor extreme climate events into how we design systems and infrastructure etc. Everyone just whacking the AC up a notch isn't going to help in the long term, as that just burns more energy.
Personally I can't hack it over 30 degrees, so I'm enjoy this cooler spell. I'm hoping it continues into August.