A survey conducted by Yale and George Mason Universities in June 2017 concludes 30% of Americans still say global warming is due mostly to natural changes in the environment. This is enticing to accept as true, because it implies the hard work of decarbonizing our economy is unnecessary. Unfortunately, all the evidence says it can’t be true. To which some might reply “Why can’t it be true? Hasn’t climate changed in the past? Human emissions certainly weren’t responsible for those changes!”

Of course, human emissions were not responsible for climate changes that occurred before the rise of human civilization. Therefore, it is logical to conclude things other than human activity can change the climate (indeed, this is the reality upon which climate science is based). However, it is a logical fallacy to then conclude human emissions are therefore irrelevant to what is happening now.

The reality is that because the earth is so massive, there are only few things that can change its temperature. The most important are variations in the Earth’s orbit, changes in solar output, and alterations of heat-trapping gas concentrations, and only the latter can explain the temperature changes we are measuring over recent decades. This is why global temperatures have risen despite solar energy output trending toward a recent minimum.

Moreover, if greenhouse gases are responsible for the warming we are observing, we should see certain predicted physical changes. For example, satellites should be able to detect less energy escaping the atmosphere at the wavelengths absorbed by CO2, and the lower portion of the atmosphere should warm while the upper atmosphere cools. In fact, these changes or “fingerprints” of human caused warming have been observed, as have many others. This is science in action: use existing theory to make a prediction, and then test the prediction with observations.

Indeed, a key reason the US Supreme Court held that the US EPA had to regulate greenhouse gases as a threat to public health and safety pursuant to the Clean Air Act is that there is no other explanation for what we are observing.

The good news is that in the Yale/George Mason survey more than half of Americans (58%) agree climate change is mostly human caused, and this is the highest this number has been since they started polling in 2008.

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