D.B.: How did you decide which solutions to include?

P.H.: We modeled solutions that are in place, practiced, understood and about which there is peer-reviewed science with respect to impact and robust economic data with respect to cost. To source economic data, we used highly respected international institutions, including the International Energy Agency, World Bank, U.N. Food and Agriculture Organization, IPCC [Intergovernmental Panel on Climate Change] and Bloomberg Energy. We erred on the side of conservatism on all data.

D.B.: How did the process help you to think differently about global warming?

P.H.: We constantly hear that global warming is an energy problem, that the solutions are solar, wind and electric vehicles. For the individual, that message sounds like I hope “they” do it. There’s a belief that there’re only a few things individuals can do beyond recycling, riding a bike and eating less meat. In fact, there’s an extraordinary diversity of solutions to global warming that are at hand, being implemented and scaling. I don’t think people, politicians and businesspeople know that. Clean energy is the crucial solution to be sure, but there’s much more we can do.

D.B.: Like what?

P.H.: Two of the top four solutions individuals can practice every day. No. 3 is reduced food waste, which particularly applies to America, where we waste 133 billion pounds of food a year — close to a third of the food supply. That is a conservative estimate. In our model we didn’t include the methane emissions caused by landfilling our food because we couldn’t get the data — and methane is 28 to 36 times more powerful in global warming potential than carbon dioxide.

The No. 4 solution is a plant-rich diet. This means reducing overconsumption of protein to a healthy level — about 50 to 55 grams a day instead of 90 to 100 or more, and shifting a proportion of that reduced intake to plant proteins. It doesn’t mean being a vegan or vegetarian; it means more plants. You choose which diet you want. Levels of protein that are medically healthier for you are healthier for the planet and atmosphere, too.

D.B.: Can you talk about the No. 1 solution? I was surprised to see that it was “‘refrigerant management.”

P.H.: We were, too. The hydrochlorofluorocarbon gases (HFCs) used in refrigerants that replaced chlorofluorocarbons (CFCs), which were destroying the ozone layer, are anywhere from 146 to 12,500 times more powerful than carbon dioxide in their global warming potential. Poorly maintained air-conditioners and refrigerators leak HFCs. When air-conditioners and refrigerators are disposed of or recycled, the refrigerants can escape into the air. We do a pretty good job preventing this in the United States, and the European Union does even better, but in Asia and Africa, HFCs are allowed to escape and have a huge impact.