Riding a bicycle is very energy efficient, but it still has externalities. Which was part of my point, everything does, even the most efficient choices.
I presumed my parent was not primarily concerned with sustainability due to bits like dead orangutans and I like beef, but I sympathize for a fellow mammal. Sympathy and orangutans are not really part of the sustainability picture, which is a separate and large issue I don't intend to dive into right now.
Eating meat can be sustainable. I'm pretty confident if we all ate crickets, there would be practically no sustainability concerns, and we can't all eat quinoa as our protein source anyway. Chile is not able to grow enough quinoa to feed the world (quinoa is a picky plant)
The 100 / 110 is purely invented as a thought experiment, but I consider it to be representative. Your daily BMR is ~2000 Calories. Engaging in activity, sports, games, or mental exercises do increase your caloric consumption for the day, but your body adjusts quickly and your additional caloric consumption for the activity falls quickly into the hundreds of calories for all but the most strenuous activities. Plus, the more strenuous (calorie-expensive) the activity, the more likely you are to take rest days, which lowers your average daily caloric consumption.
Some levels of externalities are sustainable. Some are not. The larger problem with humans is the combination of total population and average per-capita resource consumption (to say nothing of the vastly higher consumption in industrialized nations).
The steel and rubber in a bike are probably the biggest concerns (as well as the paving in roads), but in comparison with an automobile, it's vastly lower, and in comparison with the ranges and cargo capacity of walking, they're hugely higher. I've travelled 200 miles in a day by bike, and commuted over 40 miles daily for over a year at one point. One person on a bike can move a payload of many hundreds of pounds, possibly a ton or more (across level ground).
Food production at present is manifestly unsustainable. Every one calorie of food you eat in the US takes 10 in fossil-fuel energy to produce (in Europe it's about 5). Other inputs, particularly nitrogen (from fossil fuels) and phosphorus (limited global supplies) are crucial limiting factors, as are topsoil and water.
Does this activity add to the likelihood that humanity will cease to enjoy a standard of living similar to the current average at some point before other natural processes (Sun going red giant, etc.) kill us all anyway?
So hey, if they sun's gonna kill us all next year, go hog wild. If what I'm doing now means that somebody 500 years from now will have a more impoverished existence, it's not.
I took a bit of umbrage at the idea that humans surviving longer than, say, the dinosaurs did is "over hyped and misunderstood". That comment was my attempt at an unhyped and easily understood definition of "sustainability".
Three hundred mega-years (what I meant) is a somewhat arbitrary milestone. (I think long-term but 10^15 years is a bit much for even me. But see Stapledon's "Star Maker"...)
(BTW, your thinking seems unusually clear on these matters.)
I'm having a hard time trying to imagine how financially-incentivized systematic removal of the habitats of species after species after species can be considered anything but unsustainable.
People who are concerned about sustainability decry the collapse of fisheries & fish stocks, or the environmental impact of industrialized chicken farming. People who are concerned about ethics decry the destruction of pandas, orangutans, tigers, and gorillas.
None of these are good, but we don't eat pandas, so which examples of habitat destruction are used is informative.
Species extinction speaks to fundamental underlying changes to the ecosystems in which those species live.
Yes, telegenic megafauna capture hearts, but really, as apex predators or other apex species, they're the canaries in the coal mine, so to speak (and my isn't that an unsustainable metaphor...). But the waste being laid to oceans: 80% depletion of fish stocks, mass strandings of numerous cetaceans, algae and jellyfish blooms, starfish wasting diseases, and the sudden disappearances of birds, seals, and sea lions, all suggest something is going very, very wrong.
And those systems are crucial for life on Earth -- human and otherwise.
Jesus Christ, I KNOW. But which environmental issue a person chooses to talk about gives us clues to what they are thinking about. My parent's choice of orangutans suggested he was not currently worrying about long-term sustainability of ocean fisheries.
I KNOW. But, difficult as it may be to believe, sustainability still isn't what I was talking about. And, no, that doesn't mean I believe it isn't a problem.
Well, in fairness one can be concerned about the implications for the planet's health of collapsing fisheries, and also wonder by what moral authority we deprive another species that appears able to feel pain and joy of their home so we can have a diet with large amounts of concentrated vegetable oil.
I presumed my parent was not primarily concerned with sustainability due to bits like dead orangutans and I like beef, but I sympathize for a fellow mammal. Sympathy and orangutans are not really part of the sustainability picture, which is a separate and large issue I don't intend to dive into right now.
Eating meat can be sustainable. I'm pretty confident if we all ate crickets, there would be practically no sustainability concerns, and we can't all eat quinoa as our protein source anyway. Chile is not able to grow enough quinoa to feed the world (quinoa is a picky plant)
The 100 / 110 is purely invented as a thought experiment, but I consider it to be representative. Your daily BMR is ~2000 Calories. Engaging in activity, sports, games, or mental exercises do increase your caloric consumption for the day, but your body adjusts quickly and your additional caloric consumption for the activity falls quickly into the hundreds of calories for all but the most strenuous activities. Plus, the more strenuous (calorie-expensive) the activity, the more likely you are to take rest days, which lowers your average daily caloric consumption.