The Earth’s temperature changes naturally over time. Variations in the planet’s orbit, solar cycles, and volcanic eruptions can all cause periods of warming or cooling.

But Kim Cobb, a climate scientist at Georgia Tech, says none of these natural causes can explain the Earth’s current warming trend.

“What we see clearly is that the rate and the magnitude of current warming really dwarfs anything in this most recent geologic period,” she says.

Cobb says that the current concentration of global warming pollution in the atmosphere is the only factor that explains it.

“We can use global climate models to understand what would be happening if greenhouse gases weren’t in the atmosphere,” she says. “When we leave greenhouse gases out of the equation, we don’t get the warming that we’ve seen over the last several decades. When we put in those greenhouse gases, we do see this accelerated warming.”

She says the origin of all that global warming pollution is clear.

“We can tell that that’s coming from fossil fuels by studying the composition and chemical signature of that gas in the atmosphere,” she says.

So scientists are convinced by the evidence: Today’s global warming is human-caused. 

Reporting credit: Sarah Kennedy/ChavoBart Digital Media and Sara Peach