During my lifetime:
A sudden and relatively unnoticed decline in insect population. Recent studies have found a 75% decrease in insect population in the last 30 years. This has been largely unnoticed since nobody thought to measure insect population until anecdotal accounts about the noticed absence began to build. Science is now trying to catch up. One of these anecdotal accounts is termed the windshield phenomenon which points to the realization that you no longer need to clean insects off of your windshield like you used to.
Oil Industry (as a part of the network of industry including tobacco and petrochemicals) used PR firms to deliberately mislead the public about the climate emergency.
There have been three main forms of denial identified:
1. That climate change isn’t real
2. That humans aren’t the cause of it.
3. That we have plenty of time to figure it out (that techno-fixes and capital are the answer)
Fossil fuel companies have largely given up on the first two, and the third is now rampant.