Going Down the Up Escalator is an interesting post discussing the politics of separating signal from noise in climate change data. As the post notes:
Thus, by selectively picking the range of data, it is possible to argue that the temperature is cooling rather than warming (as shown in the graphs below).
There are also a number of effects which can have a large impact on short-term temperatures, such as oceanic cycles like the El Niño Southern Oscillation or the 11-year solar cycle. Sometimes these dampen global warming, and sometimes they amplify it. However, they're called "oscillations" and "cycles" for a reason - they alternate between positive and negative states and don't have long-term effects on the Earth's temperature.