It's part of human nature. It's what we do. We develop a form of mild amnesia about our reality of twenty or thirty years earlier as we accept our current state as "normal."
The Guardian's enviro-scribe, George Monbiot, writes that our selective blindness is lethal.
As the psychologist Richard Wiseman points out: “At any one moment, your eyes and brain only have the processing power to look at a very small part of your surroundings … your brain quickly identifies what it considers to be the most significant aspects of your surroundings, and focuses almost all of its attention on these elements.” Everything else remains unseen.
Our selective blindness is lethal to the living world. Joni Mitchell’s claim that “you don’t know what you’ve got till it’s gone” is, sadly, untrue: our collective memory is wiped clean by ecological loss. One of the most important concepts defining our relationship to the natural world is shifting baseline syndrome, coined by the fisheries biologist Daniel Pauly. The people of each generation perceive the state of the ecosystems they encountered in their childhood as normal and natural. When wildlife is depleted, we might notice the loss, but we are unaware that the baseline by which we judge the decline is in fact a state of extreme depletion.
So we forget that the default state of almost all ecosystems – on land and at sea – is domination by a megafauna. We are unaware that there is something deeply weird about British waters; they are not thronged with great whales, vast shoals of bluefin tuna, two-metre cod and halibut the size of doors, as they were until a few centuries ago. We are unaware that the absence of elephants, rhinos, lions, scimitar cats, hyenas and hippos, that lived in this country during the last interglacial period (when the climate was almost identical to today’s), is also an artefact of human activity.
And the erosion continues. Few people younger than me know that it was once normal to see fields white with mushrooms, or rivers black with eels at the autumn equinox, or that every patch of nettles was once reamed by caterpillars. I can picture a moment at which the birds stop singing, and people wake up and make breakfast and go to work without noticing that anything has changed.
I can tell my children of a world of which they'll have no experience. Their memory starts somewhere in the 90s and it's been in flux ever since. The climate in which I grew up seemed not appreciably different than the climate during my parents' and grandparents' youth. That climate, the tail end of the Holocene, is gone and it's not coming back. Now we're into the Anthropocene and a climate far less benign.
I know from my memories that today is not normal because I have something to measure today against. They have no such memories, no similar yardstick. Their today is normal.