4.5 watts isn’t very much.
That’s a negative 4.5. And you are forgetting that the Sun and the Earth are going to be about 2 million miles further apart so a -4.5 becomes more important ... Lots of people have done the math - no one has gotten a different answer. Average Earth temp (as best we can tell) was 1.1 degrees cooler during the Little Ice Age ... this period will be colder by a lot. The wattage effects the temperature - its the Sun! The lower the wattage, the lower the temperature. The further from the Sun, the cooler the Temperature - its the Sun!