It’s the sun, dammit!
I’ve just finished watching The Great Global Warming Swindle - a Channel 4 documentary that basically states that something we’ve begun taking for granted, is really resting on shaky scientific grounds.
Key arguments: CO2 in the atmosphere lags behind temperature changes by about 800 years. It’s the old "correlation does not equal causation" again - there might indeed be causation between CO2 and temperature, it’s just the other way around.
The sun, that gigantic energetic nuclear furnace in the sky, is what’s driving Earth’s atmosphere: 
Thus, it’s really not surprising that we’re seeing the temperature and CO2 rise at the moment, since it’s about 800 years since the Medieval Maximum . (They have actually been rising since the late 18th century) "The sun is driving climate change, CO2 is irrelevant" - Dr Piers Corbyn