It's volcanoes and it's been demonstrably proven. Here's the fun part, I was watching a program with Canadian George Kourounis where they were testing volcanic gas output at as many locations as possible. They were mainly looking for CO2 emissions.
George concluded that volcanoes were not the problem because they accounted for only 0.2GT of CO2 per year while humans produce 35GT per year. But his method was highly flawed. They only tested those volcanoes that are above sea-level. Given that the lowest estimate for the number of submarine volcanoes, vents, stacks and smokers is about 1000 times as many as we can see on land, simple extrapolation would strongly suggest that volcanic activity produces just shy of 6X the amount of CO2 per year as human activity.
But I'm sure you have nothing to worry about. After all "scientists" convinced us that tobacco was not only safe but medicinal. They convinced us that animal fat is bad but sugar is fine and dandy. They convinced us that companies like Monsanto only have the most altruistic aims. And now they've convinced you that humans are the primary driver of climate change. Despite the fact that A) Climate change is always happening, we don't live in a static environment. And B) The climate changed numerous times before humans were even twinkle in Mother Nature's eye. Why would we stupidly assume that despite the fact we just came out of a mini-ice age, all the warming is the fault of humanity? You have to be some special kind of stupid to buy that shit, even for a dollar.