The US is cold right now, largely due to very dry air. Note that dew points are below 0C across almost the entire country. This has two effects – it reduces the greenhouse effect, and reduces the amount of heat being generated from condensation.
Now compare vs. Saudi Arabia, which has much higher humidity with dew points in the 10-20 C range.
And Australia which has dew points in the 10-30C range.
Also note that reduced temperature further reduces the amount of longwave radiation being generated by greenhouse gases in the atmosphere.