The smoking gun is...
FACT: The CO2 level is rapidly increasing as fuel burning has increased
FACT: The atmospheric isotope ratios of carbon are rapidly changing from what they were
FACT: The isotope change is not possible to explain with volcanism
FACT The isotope change IS consistent with what you would expect from burning of fossil fuels.
FACT: Increased CO2 will cause global warming
FACT we are seeing warming...
I will look up the charts and pretty pictures, but feel free to research it yourself.
