Extreme cold has decreased sharply. Since the 1990s, the frequency and severity of record-cold winter temperatures have dropped substantially.
Weather is not climate. So you'll still expect to see a record cold for some area or another for a short time, even if the average temperature is climing. This is why you should see what climatologists say, not alarmists or deniers.
For one thing, you look at theories that have made predictions. In the late 1800s, scientists began to realize that more carbon in the atmosphere would mean warmer average temperatures. A few decades ago, a NASA scientist actually predicted the rate of increase as a consquence of increasing carbon. Both predictions have been confirmed.
Given that there are no humans on Pluto, we can rule out anthropogenic carbon as a cause. Also it has a very, very thing atmosphere, so that wouldn't be a factor, either. However, Pluto has a very eccentric orbit, sometimes coming closer to the Sun than Neptune. It was closest to the Sun about 30 years ago, and since it takes about 248 years to orbit the Sun, it's not surprising that it's warmer than usual now.
How do deniers deal with this fact? Generally, they don't know about it, so it's not a challenge to their assumptions.