How is global warming proved?

Answer 1

First, we compare a whole bunch of temperature measurements. If the average is constant or declining, then the earth is not warming.

We have done that, and the evidence points conclusively to significant temperature increases, particularly over the past 30 years.

Second, we need to examine a list of possible causes. One is that the sun might be producing more energy. It isn't. Another is that periodic orbital cycles might explain the temperature increase. They do not. A third is that some other unknown natural cycle might be at work. If there is such a thing, it remains entirely unknown. A fourth is that human forcing 40 billion tons of heat trapping CO2 into the atmosphere each year might be having some cumulative effect.

Scientists have examined this last hypothesis with considerable care, and in general have concluded humans are indeed responsible for at least 95% of the current warming trend. The remaining 5% of global warming remains unexplained. It might also be due to increased CO2, or there might be some other explanation for it.