You should continue your dialogue with the warmists by asking questions. For example ask how their experts explain the hiatus. And if they answer ask how their experts explain the mechanism used when the missing heat goes to the deep waters? Some numbers, maybe?
Easy questions are also revealing. What is the global average temperature? What happens if it rises to super hot 17 C. Are we toasted? What will be different? OK. Every Canadian knows the there is too hot in the USA. But what about Siberia, Greenland, Alaska and so on. What is the optimum temperature for mankind?
Most of the modelled warming is not coming from CO2 but from the chain-reaction of warmings created by CO2 at first and after that by consequences of that warming. If there is no measurable warming, does the heat created by the secondary effects exist or not?