Rebuttal to climate change denier



A recent letter from a self-professed climate denier (Letter, “Greenhouse gases and how they work,” Dec. 1, The Express) is correct when making the point that water vapor is indeed a potent greenhouse gas.

But how does water vapor get into the atmosphere to begin with?

Without heat, there would be very little water vapor in the atmosphere. It is the reason why it doesn’t snow much in Antarctica. It’s just too cold to hold much moisture in the atmosphere.

Science shows that the amount of water vapor in the atmosphere is directly related to temperature. As temperatures increase, more evaporation occurs, putting more water vapor in the atmosphere. The more CO2 we put in the atmosphere from burning fossil fuels, the hotter it gets, which generates more evaporation and more water vapor.

Scientists call this a positive feedback loop. But it’s anything but positive. Water vapor is a potent greenhouse gas, so more water vapor increases global temperatures. Studies show that water vapor feedback roughly doubles the amount of warming caused by CO2.

The good news is if we reduce carbon pollution, the amount of water vapor in the atmosphere will also decrease because water vapor has a residence time of only about 10 days, whereas CO2 lasts for centuries.

So, the climate denier was right in saying that water vapor is the dominant greenhouse gas.

The water vapor feedback loop actually makes temperature changes caused by CO2 even bigger. And without CO2 driving temperatures up, there would be a lot less water vapor.