What are some misconceptions about global warming?
The biggest one is probably confusion between "climate" and "weather".
Many people have expressed doubts that global warming is happening on the basis of events such as "very cold winter" or "round our way, we had snow in March - so much for global warming!".
Global warming relates to the average temperature of the whole planet, and the fact that this is increasing does not prevent specific areas of the planet from experiencing weather events that do not relate to high temperature. In fact, increasing mean global temperature is more likely to result in increasingly erratic weather events in different parts of the planet.
The biggest misconception about global warming, therefore, is the observation of a specific localised weather event, and attempting to relate this to what is happening on a global scale.
But to say "Where I live we didn't have a very hot summer this year, and last winter was really cold so global warming cannot be happening" is a bit like watching two people emerging from a subway train, noting that both of them seem to be no more than around 5' tall, and assuming from this observation that the entire human race is shrinking!