There may be a fair comparison made between the situations. For instance, in the 19th Century, there were industrial revolution related changes that permitted the rise of huge urban population centers. By the 21st Century, technological changes, medical breakthroughs, the green revolution, a thriving worldwide commerce, scientific advances, modern communication and transportation systems, etc., have all combined to support vast increases in the population on all continents except Antarctica.

In 19th Century America and Europe, the changes that corresponded with the increases in urban population did not come with an appreciation for many of the potential consequences of rapid metropolitan growth. In the 20th and 21st Century, little serious attention had been paid until recently to some of the adverse consequences of rapid planet wide growth.

In the 19th Century, the advances in industry that permitted the beginnings of a switch from primarily agrarian to mainly urban lifestyles were not yet matched by an increase in sophisticated community health knowledge. In the 21st Century, there was initially not a widespread recognition of long-term cost benefit considerations, that might have shown the relative advantages of environmentally safer approaches vs. ones that have emphasized chiefly the short-term convenience of carbon-based energy sources.

In both the 19th and 21st Centuries, little overall planning went into the respective rapid rises in local or global populations. Thus, in both instances people neglected the importance of our waste products (feces, in the 19th Century, and carbon dioxide or other pollutants, in the 21st Century) in the overall equation.

Ozone Depletion over Antarctica (NASA)

In each century, once there was dawning awareness of the difficulties and their causes, there was also an inertia-like resistance to their acknowledgment. In both cases, powerful, vested commercial and political interests successfully sought for extended periods to maintain the status quo rather than to mandate (or even acquiesce to) indicated changes urged by respected scientists or community leaders. (I do not here mean to single out any political party or sectors of our economy. In a sense, most everyone has been involved in what has occurred. There are few in the developed world so "pure" as not to have seriously contributed to the challenges all are now facing, and it appears third world nations such as China, understandably eager to share for their populations in the best that swift material progress has to offer, are now intent on matching the sort of excessive environmental degradation modeled for them by countries like the U.S. that have already "made it.")

One result was that, in the 19th Century, major cities sometimes had to deal with quite preventable but nonetheless repeated, massive cholera infections. As yet, we are still determining the consequences of earlier inaction over, and continued forestalling of, major needed remedies for global warming. But it seems probable that, by about 200 years from now, our descendants will be dealing with a significantly hotter world, less reliable food production, less viable development in coastal areas, greater storm damage, higher disease incidence, adverse chemical and biological shifts in the seas, insufficient sources of potable water, and staggering losses of populations among land and water species.

The public health issues and conditions that led to massive human die-offs in the U.S. and Europe a couple centuries ago have not gone away. Rather, as the population has continued to increase, parallel, though differently realized, implications are now playing out on a planet-wide stage. Tens of thousands of people were directly affected by each of several instances of 19th Century cholera outbreak. With the combination of large increases in and diverse spreads of both the population and pollutants (allowed, just as two centuries ago, to rise to dangerously beyond-threshold levels), the negative consequences of an inadequate resolution of 21st Century waste product problems could this time be on a far greater scale.