Think of it like a who-dun-it mystery. Scientists have identified all the "usual suspects" sun, aerosols, land over, volcanoes, etc. Each suspect has its own fingerprint, "calling card," and DNA signature. The warming we see match CO2 almost perfectly, and none of the others match well at all.
“That’s a coffin with so many nails in it already that the hard part is finding a place to hammer in a new one.” — Geophysicist Ray Pierrehumbert.
Saying "climate change happened naturally in the past, and therefore human's can't cause it" is like saying "forest fires occurred naturally in the past. So there can't be arson."
Variation: Arson and camper carelessness can't cause fires, because forest fires often occurred naturally before people even existed!
"Some say, 'Climate is always changing due to natural cycles. So it can't be us doing it.' That's like saying 'People die from natural causes. So there can't be murder!' Any good crime investigator must develop expertise on natural causes of death, so he can distinguish it from foul play. Same with climate scientists." — Dr. Richard Alley
The bad news: we are causing it.
The good news: we can stop it.
Humans have overrun the planet to live in every ecosphere. We have had a dramatic impact on natural resources in every land we have colonised. But our impact pales in comparison with plankton.
Every day, beer is delivered to a restaurant in crates, and the driver takes away the empty bottles from the previous day in the same crates.Now, living above the restaurant is a man who likes to drink the same brand of beer. Each day he buys a bottle at the corner store on his way home from work and having drunk it while watching TV, he takes the empty downstairs. Knowing that nobody will notice just one extra bottle, he puts it with the big pile of empties outside the restaurant. After just a year the restaurant rings the brewery and complains of the huge pile of empty bottles outside their rear entrance. The brewery comes round to collect the empty bottles and fills dozens of crates to take away the 365 empties. Nobody — the man upstairs included — can figure out where they all came from!
"It may not be common sense, but if common sense were good enough, we wouldn't need science."
Slowing emissions of carbon dioxide is somewhat like slowing credit-card spending and expecting your debt to shrink.
Human's aren't the first species to alter the atmosphere; that distinction belongs to cyanobacteria, (blue-green algae) which, some two billion years ago, invented photosynthesis. But we are the first species to be in a position to understand what we are doing.
"Past climate change is not a source of comfort. It's a cause for concern."— John Cook
Mark Twain famously said, "Everybody talks about the weather, but nobody does anything about it." It turns out that he was wrong. We have been doing something...but unintentionally and not for the better.
"An obese, middle-aged man is running to catch a bus. Suddenly, he clutches his chest, falls to the ground and dies of a massive heart attack. It turns out that he's a smoker and a diabetic, has high blood pressure, eats a diet high in saturated fat and low in leafy green vegetables, pours salt on everything, drinks too much beer, avoids exercise at all costs and has a father, grandfather and two uncles who also died young of heart attacks. So what killed him? Most people are savvy enough about health risks to know this is a trick question. You can't pick out a single cause. His choices and his genes all contributed to the heart attack — but you can say with confidence that the more risk factors that pile up, the more likely it is to end badly."
“...When it comes to climate change, it's the fossil fuels we insist on burning—particularly oil—that are the single greatest cause of global warming and the damaging weather patterns that have been its result.” — Barack Obama
Global warming, like obesity, is an unanticipated consequence of prosperity.
There are only a few plausible explanations for changing climate. To be accepted as a robust explanation for global warming, Greenhouse Gases don't have to win the Explanation Race at the speed of light, they just have to be better than all the other explanations.