It's easily done. Most of it is out of sight, out of mind. Some of it happens hundreds, thousands of miles offshore. Some of it simply cannot be seen. When we can see it we usually choose to look the other way.
Deutsche Welle lists the five biggest man-made threats to our oceans as:
2. Ocean acidification
3. Ocean warming
4. Pollution of all description, and
5. Seabed mining.
Most of us don't pay much heed to our oceans or what's underway there, the changes that are already occurring. We hear a lot about the plastics problem but, as threats to our oceans go, that's fairly modest.
Few people I've met realize the magnitude of the acidification threat and how it may have been instrumental in all but one of Earth's mass extinctions. For more on that, read Peter Ward's "Under a Green Sky." Or, you can read this one key paragraph from Ward's book:
First, the world warms over short intervals of time because of a sudden increase of carbon dioxide and methane... The warmer world affects the ocean circulation systems and disrupts the position of the conveyor currents. Bottom waters begin to have warm, low-oxygen water dumped into them. Warming continues, and the decrease of equator-to-pole temperature differences reduces ocean winds and surface currents to a near standstill. Mixing of oxygenated surface waters with the deeper, and volumetrically increasing, low-oxygen bottom waters decreases, causing ever-shallower water to change from oxygenated to anoxic. Finally, the bottom water is at depths were light can penetrate, the combination of low oxygen and light allows green sulfur bacteria to expand in numbers and fill the low-oxygen shallows. They live amid other bacteria that produce toxic amounts of hydrogen sulfide, and the flux of this gas into the atmosphere is as much as 2,000 times what it is today. The gas rises into the high atmosphere, where it breaks down the ozone layer, and the subsequent increase in ultraviolet radiation from the sun kills much of the photosynthetic green plant phytoplankton. On its way up into the sky, the hydrogen sulfide also kills some plant and animal life, and the combination of high heat and hydrogen sulfide creates a mass extinction on land. These are the greenhouse extinctions.
This is the process that's starting again and driving it are those petro-pimps of Parliament Hill, the lot of them on both sides of the aisle.