Here are Gifs that describes the changes in Earth's orbit around the Sun and why it effects Climate change. This, IMO, is the primary reason for why we see Climate change.
Here is a Gif that illustrates the Earth's rotation around the Sun. Taking into account the axis variance of the Earth and the fact that it moves between a tilt of 22.1 degrees and 24.5 degrees at any given time in it's rotation around the Sun, the mean temperatures in any given part of the world can change because the amount of direct radiation from the Sun changes. Temp changes either increase or decrease the amount of Carbon into the atmosphere, which in turn, create Temperature variations.
Remember that the Sun is also rotating and that it also sits a tilted axis as well. I believe that the Sun's axis tilt is approximately 7.5 degrees of true vertical. Also keep in mind that certain spots on the Sun burn hotter then others. What does this suggest? It suggests that depending on where the Earth is in it's rotation around the Sun, the Tilt of the Earth, the rotation of the Sun and it's tilt can account for short term climate conditions because again, certain points on the surface of the Sun create more direct radiation hitting the Earth via Solar Flares etc. Another variable is the actual amount of time the Earth is closest to the Sun and how the speed of the actual rotation around the Sun, in accordance with where it is in it's trajectory pattern around the Sun effects temps. This is why you seem short term periods where it may be hotter or colder.
It's much more complicated then this, obviously, but I guess what I'm trying to say is that this is much more a normal phenomenon, IMO, then anything Man is currently doing or not doing.
We won't even get into the discussion of the fact that all celestial bodies are moving outward and that over time, our own solar system is also expanding away from each other, which in turn, causes a cooling effect. That's another discussion all together.