Climate change may not be forever, but it’ll be for a long, long time. Who -- or what -- will be around thousands or millions of years hence, when the consequences of our casually massive carbon emissions are still playing out? And do we owe them anything?

According to philosopher William Grove-Fanning, currently at the Environmental Studies Program at Trinity University in San Antonio, the phrase “future generations” first started showing up in the late 1960s, in discussions of bioengineering and nuclear waste. These days, it shows up constantly in discussions of climate policy (and on “Seventh Generation” household products marketed to the eco-conscious -- but no longer bought by our household since we noticed that they dye their diapers brown to make them look more ‘natural’ or ‘recycled’). As the climate changes, it won’t just -- or even mostly -- affect those alive today. We may bite the big one before things get truly strange and/or horrendous. But people toss off the phrase “future generations” so glibly, without really specifying whom they are talking about.

Grove-Fanning figured that most people probably imagine their grandchildren or great grandchildren. And most people are right; the next two or three or four generations may well suffer a great deal thanks to our actions. But, by sheer numbers, there will be more people in the many, many future generations after that. So even if the worst harm will be in the “short” term of the next few hundred years, the vast majority of the people who will suffer at least some harm are in the far future. To figure out how far, in both time and genetics, he did some research on two questions:

1. How long will the effects of climate change last?

2. Who will be around at the end of that period?