It is obviously true that past climate change was caused by natural forcings. However, to argue that this means we can’t cause climate change is like arguing that humans can’t start bushfires because in the past they’ve happened naturally. Greenhouse gas increases have caused climate change many times in Earth’s history, and we are now adding greenhouse gases to the atmosphere at a increasingly rapid rate.
Looking at the past gives us insight into how our climate responds to external forcings. Using ice cores, for instance, we can work out the degree of past temperature change, the level of solar activity, and the amount of greenhouse gases and volcanic dust in the atmosphere. From this, we can determine how temperature has changed due to past energy imbalances. What we have found, looking at many different periods and timescales in Earth's history, is that when the Earth gains heat, positive feedbacks amplify the warming. This is why we've experienced such dramatic changes in temperature in the past. Our climate is highly sensitive to changes in heat. We can even quantify this: when you include positive feedbacks, a doubling of CO2 causes a warming of around 3°C.
What does that mean for today? Rising greenhouse gas levels are an external forcing, which has caused climate changes many times in Earth's history. They're causing an energy imbalance and the planet is building up heat. From Earth's history, we know that positive feedbacks will amplify the greenhouse warming. So past climate change doesn't tell us that humans can't influence climate; on the contrary, it tells us that climate is highly sensitive to the greenhouse warming we're now causing.
I'm not arguing that it's impossible for humans to effect climate, if Earth's inhabitants couldn't effect climate, we wouldn't be here today.
My point is when you compare the effects of common events, such as volcanic eruptions and solar cycles, those have much greater effects than we are capable of doing. A single volcanic eruption can cool the global temperature within days.
I haven't read too much about man made climate change, it's not like its easy to find credible sources you can actually believe. When you have scientists emailing each other on how they can curve fit figures to prove their points. When what was supposed to be the biggest ecological disaster in history, disappearing on its own in the gulf of mexico. When you can still walk about in chile without sunscreen and not get fried like an ant. It makes it all the more harder to buy into the whole man made climate change thing.
Don't get me started on all the money behind it either. The only people I see who buy into all the energy efficient light bulbs, low flow toilets, etc. Are people who don't stop and think how having to flush 6 times instead of once saves energy, or how its better for the environment to have light bulbs that are full of toxic chemicals, that even have an eerie green glow when they are turned off. Electric cars are nice too, because nobody stops to think "Hey, I wonder how electricity gets to my house." They just think that its actually a *different* kind of energy flowing from their house to the outlet, to their car. It's not a bunch of giant power plants burning fuels to generate energy, its magic!