Plus the satellite data may be off by 30%.
Most people are unaware of just how twiddled and mysterious the satellite data is. In comparison, surface temperatures are beacons of simplicity, transparency and reliability. But since the unreliable RSS satellite data tells the deniers what they want to here, the deniers disregard the good data and rely almost exclusively on RSS now.
Here's a file from the UAH satellite data people, describing some of the fiddling they do. Their intentions are obviously good, but they're working a very difficult task. As soon as they work the bugs out of one satellite, it fails and they have to shift to a new satellite with a totally different calibration.
http://www.nsstc.uah.edu/data/msu/t2lt/readme.06Nov2014