Whilst not denying global warming, I think it is incorrect to say that August had the coldest synoptic setup possible. Most of the August's northerlies circulated around the Azores High, not sourced from the Arctic.
The point has also been made that August 1995 had a high proportion of northerlies, and it wasn't exactly nippy either....
I suspect that with the coldest synoptics a month would still be cold, but just 0.5-1.0 higher than it would have previously. The question is of course whether GW has changed synoptics, my suspicion is yes, but it still doesn't rule out the occasional cold month.