A single "phenomenon". Several "phenomena". (Science still uses Latin-style singulars and plurals.)
– Sprayed pesticides are getting out of control, and kill honeybees that have been brought into orchards and fields to pollinate the crops.
– People are discarding plastic items such as throw-away water bottles, which are ending up in rivers and trash dumps, and eventually in the oceans. Large amounts of plastic junk are being ingested by fish and marine mammals, often killing them.
– There's still disagreement about the extent to which human activity is increasing the carbon dioxide content of the atmosphere, and how much this is causing climate change ("global warming"). Major swings in the world's climate have taken place even within human history, such as the chilling during the Middle Ages, when Viking settlements in Iceland, Greenland, and even North America gradually had to be abandoned because it had become too cold to grow crops. Are we humans simply experiencing the warming phase of such a swing, or are we actively contributing to it? Or both?