We know that CO2 warms the world, that CO2 concentrations are at record-breaking levels, and that global temperatures are rising. But how do we know for certain that humans are the cause?
The answer is in the science. The CO2 produced from fossil fuels carries a unique signature that differentiates it from CO2 produced from other sources. In brief, it carries a specific ratio of carbon isotopes that is only found in the atmosphere when coal, oil, or gas is burned.
Scientists call this δ13C (pronounced "delta C thirteen"), and it’s a smoking gun. Since the 1880s, δ13C has changed in a