No warming for only 18 years? Depends on what you look at. Average temperature? Just remember that the average of 51 and 49 is 50 and the average of 99 and 1 is also 50. You might as well consider the significance of the average telephone number in New York. The real information is in the Maximum and Minimum temperatures.
Here's what you get if you go to NOAA's Climate at a Glance and specify Max Temp June - September and the trend since 1930 for the Contiguous United States:
There are 20 states where the cooling trend for summer afternoons extends all the way back to the 19th century. Here's a map showing where the cool down has occurred:
What this means is that because the average temperature has indeed increased, it's the Minimum Temperatures that have gone up. Indeed that's what the IPCC reports tell us. The warming will be at night in the winter and in the higher latitudes. In other words the climate has become milder. When our media talking heads tell us about extreme weather becoming the new normal they will have to begin telling us about extreme mildness.