At the cutting edge of climate research, individual extreme event attribution now takes only days to quantify the human fingerprint.
The latest analysis shows that the crippling early season heatwave enveloping the lower US and Mexico is 35 times more likely due to human-caused climate change.
Climate change has permanently altered the background conditions against which extreme events occur. So for any given event, it contributes somewhere between 0-100% in terms of increasing the likelihood, severity, and/or duration. The longer our emissions continue, the higher the average percentage.
None of the events we see would have happened without it.
Other events of similar type would have happened but they would have been fewer and less severe on average.
So 0% contribution is unlikely, but does it still happen? Actually, I can only imagine that to be the case in the tiny spots on earth where there is a relative cold-spot. Please clarify.