Okay, let's define "mainly caused" first. I take that to mean more than half of the observed warming since the industrial revolution is due to human activity. The evidence on that is clear. We've increased CO2 in the atmosphere by nearly 50% since the 1800s. That's a fact from ice cores and direct measurements. CO2 is a greenhouse gas. It traps heat. Basic physics. So we pile on more CO2, the atmosphere holds more heat. And the warming we've seen matches that fingerprint perfectly—the pattern of warming, the way the upper atmosphere cools while the surface warms. Natural factors like volcanoes or solar changes just can't explain that pattern. So when you look at the math, it's not even close. Humans are the main driver.

Let me ask you something: if natural cycles explain the warming, why does every climate model that only includes natural factors fail to match what we've actually seen? They show flat or cooling temperatures since 1950. But the models that include human emissions? They nail it. You mentioned water vapor being the dominant greenhouse gas. That's true. But here's the thing—water vapor is a feedback, not a forcing. It responds to temperature changes, it doesn't drive them. And CO2 is what kicks off that process. We add CO2, it warms things a little, then more water vapor enters the air and amplifies it. That's basic climate physics. And yeah, CO2 was higher millions of years ago. But the sun was also weaker back then. You can't just cherry-pick one number and ignore the rest of the system. The rate of change matters too. We're pumping out CO2 faster than anything in the geologic record. That's what makes it different.

Let's get one thing straight—the ocean carbon cycle you mentioned actually supports my side. The ocean absorbs about a quarter of our CO2 emissions. If it were releasing carbon naturally, we'd see a different isotopic signature in the atmosphere. But the carbon we're measuring has the fingerprint of fossil fuels. That's not theory, that's forensic chemistry. And yes, CO2 sometimes lagged temperature in ancient ice cores. That's because those were natural cycles starting with orbital changes. But now we've got CO2 leading temperature. We're the ones pushing the lever first. The relationship flipped because we're the forcing, not the feedback. Your point about complex systems is fair. But complex doesn't mean unknowable. We understand the physics well enough to know that the warming pattern we see—stratosphere cooling, surface warming, more heat at night—only happens with greenhouse gas increases. Natural factors don't produce that fingerprint.