The above photo displays the cumulative effect of a dozen ground-disturbing projects upon a 60-acre parcel of mixed-grass prairie in western North Dakota over the course of 70 years. It is likely that, as each project came up for consideration, someone determined that the action would have a minor impact on the landscape. But in aggregate, the twelve projects resulted in a major impact upon the landscape; persistent scars indicate widespread habitat degradation, corridors for invasive species, erosion, failed prairie regeneration, loss of biodiversity, loss of species, loss of original ecosystem components, loss of original ecosystem characteristics, and so forth.
This may bring to mind a tragedy in New York City, 1933.
That year, a 50-foot tall gigantic, semi-humanoid gorilla scaled the Empire State Building and took on modern civilization, swinging his powerful arms at the sky. Four Curtiss F8C-5/O2C-1 Helldivers, a 1920's Marine Corps biplane, swarmed the prehistoric ape and fired upon him with their .303-caliber Lewis guns, two fixed forward firing guns and one flexible rear cockpit gun. While the .303-caliber bullet was designed to kill humans, against a simian of that size, each bullet would be proportional to a .038-caliber bullet fired at a six-foot man. That's about the width of a mechanical pencil lead.
This is impractical. A war fought with mechanical pencil lead would take hundreds of years to wage, reducing, by comparison, the wars between the Kings of England and the Kings of France to a mere border skirmish, and risking, in theory, a rapid descent into world peace. To overcome this handicap, Kong was assaulted by four biplanes with a total of 12 Lewis guns for nearly three minutes, firing their guns in seventeen one-second bursts. As many as 170 rounds of ammunition may have penetrated his shimmering latex and rabbit-fur hide. One bullet alone wouldn't kill him, but the cumulative effect of 170 rounds had a significant, lethal impact. Bleeding badly, Kong tumbled from the spire and landed at the intersection of 5th Avenue and West 33rd Street, where a drug store and hair styling salon stand today.
Thus, cumulative effects are like biplanes swarming King Kong. One project alone may not carry enough firepower to adversely impact an ecosystem or population. But dozens, hundreds, or thousands of these projects may have enough collective firepower to have a significant lethal impact. The population or ecosystem may hemorrhage, weaken, and tumble to its death.
This collectivism can be hard to see. Sometimes an assessment that determines that a given project will have no significant impacts may be compiled in ignorance, without awareness of previous, current, or future projects that impact the same area. Some may say that this would be as if the four F8C pilots did not know of each other's existence, but the analogy falls apart when one realizes that pilots didn't set out to wound Kong, extract some essential bodily fluids, then let him heal up, rather, they intended to kill Kong.
Well, this leads us into a protracted debate about our legacy of unintended and unanticipated consequences, that we just can't know every past, present, and future impact around us, nor can we know the sum total of these impacts - a sum that is growing daily and is significantly greater than the sum of its parts - but with a long history of battling beasts to extinction, we have to wonder if it's beauty that is killing the beasts or if our beauty is only skin deep.