So why have there been cold snaps in Washington and London if the planet is warming?
Climate change marks a transition between a (recent past) stable period of predictable global climate and another, as yet unknown, one in the future, where temperatures on a global average will be higher.
When any system moves from one stable position to another there is always a period of instability and turbulence in between.
The study of this is called complexity theory and uses mathematical models developed from non-linear chaos theory.
A parallel analogy is, for example, an aeroplane changing its angle of flight from level (stable) to vertical (falling from the sky, but still linear). In between it will stall, and this is when occupants would feel their ride to be very bumpy.
Transferring the analogy to weather - weather is a local variant of climate.
Instability in the climate will therefore result in local 'bumpiness' - unusual and extreme local weather conditions. In some places this will mean occasional extremely cold, stormy or hot weather.
To think that an episode of local cold weather means that the whole world is getting colder, or even not warmer, as climate sceptics do, is almost like thinking that if the lights fail in your building, it's the same all over the world.