The problem I have is that if our climate changes, it must do so because of some change in physical parameters. There are lots of answers referring to natural cycles and climate changing before, but these answers conveniently avoid discussing the causes of those cycles or changes. The climate of our planet changes because of a change in solar activity, or a change in the amount of energy arriving at the earth, a change in the planet's albedo, a change in orbital position, and so on. In other words, there is a physical cause or multiple physical causes.
Our planet is warming due to the vast amounts of CO2 we're pumping into the atmosphere, and this is amplified by an increase of water vapour due to that warming. It's not the sun, or changes in orbital position, or some other 'natural' factor. It's us! We've spent 40 years getting to the bottom of it. Since CO2 mixes in the atmosphere, the CO2 we're pumping today will still have an impact in 100 years time. Our planet is going to get warmer. How warm depends on how quickly we start to reduce our CO2 emissions.
Now yes, this does not mean natural processes are not occurring. But whether there is an ice age in 50,000 years isn't the pressing issue. Whether it was warmer in the past or cooler in the past doesn't change the fact our planet will warm over the next few centuries unless we get our CO2 emissions under control. Yes, the sun is going through a cooling period, but this will amount to less than a 1% change and every calculation suggests it won't be enough to reverse the warming trend we're seeing.
What some skeptics are basically arguing is that it is possible to increase CO2 levels in our atmosphere but not impact the temperature of the planet. This, to me, is as scientifically ludicrous as arguing the planet is flat. I know they really, really want to believe everything and anything under the sun (and the sun itself) is responsible, but that's no longer a realistic argument anyone can take seriously.
Now, if you look at Daro's graph, what it shows are changes occurring over very long timescales. We know that CO2 levels change naturally by 100 parts per million over periods of 5000 to 20000 years. We've managed to increase CO2 levels from 300 to 415 parts per million in about 130 years. That is what is driving the warming climate we are observing and will continue to observe over the next few centuries.
The debate in most countries has moved on to what we do about it, not whether we are causing it. It is only in the US that we see this sort of opposition ... why is it that people in a country that is a major consumer and producer of fossil fuels are resistant to the concept of fossil fuels being a problem? Hmmm ... I wonder ...