Our oceans cover over 70% of the surface of the Earth, to an average depth of 12,000 feet; the deepest the Mariana Trench at 36,000 feet, and with a staggering volume of 1.4 billion cubic kilometres, numbers the late Carl Sagan could appreciate.

Their vastness has meant that only a tiny fraction has been explored, or is explorable.

Knowledge of our oceans is miniscule. We know more about outer space, yet it’s our oceans that we rely on as our life support, supplying 50% of the oxygen in our atmosphere, while absorbing excess heat, carbon dioxide, and wastes of all kinds from human activities.

Oceans are our climate change insurance policy against an unlivable planet, but in our ignorance wrongly assumed that they had infinite capacity to absorb our wastes, with few consequences.

Hold a flame under an air filled balloon and it will burst almost immediately. Repeat with one filled with water and you will be standing there indefinitely. Up until now we have relied on our oceans to absorb 90% of the excess heat from global warming, to regulate the planet’s temperature, a massive heat and CO2 sink without which the planet would be uninhabitable.

We have overshot the considered safe threshold of 350 ppm CO2, and are now at a dangerous 425 ppm, and climbing. 

Warming oceans, with temperatures at record levels, have altered weather patterns, driving more intense rainfall events, storms and hurricanes.

The combination of ocean warming, melting glaciers and ice sheets is causing ocean expansion and sea level rise. Melting ice alters the density of seawater which, in turn, can affect ocean currents that moderate our climate.

As ocean temperatures rise and oceans acidify, there will come a tipping point, some scientists say around 2100, when these waters will be able to absorb significantly less CO2.

In light of this year’s shattering of previous temperature levels, I believe that this is an overly optimistic appraisal. Deforestation and massive wildfires make it a double whammy.

Our oceans are a food source for 3.5 billion people, yet we are altering marine ecosystems in ways scientists don’t fully understand, threatening this resource.

We know the damage that acid rain from smelting and coal burning caused to our forests, lakes, soil, and human health. Now we are acidifying our oceans with carbon dioxide, reducing the ability of shellfish and corals to make their shells and skeletons.

In 2024 ocean temperatures in Florida reached new highs, with some parts of the Pacific 5°above normal. Heat is stressing coral reefs worldwide, leading to bleaching and die-off. The iconic Great Barrier Reef has recently suffered its worst ever bleaching event. Reefs act as nurseries, providing habitat for 25% of marine species, but as reefs bleach and die we are hastening species decline.

Overheating, pollution and acidification further threaten marine species, at a time when growing populations will become increasingly dependent on them.

Ocean temperatures, at the surface and in the deep reaches, have set new records. These changes have had harmful effects on marine life. In addition to these insults, we are rapidly depleting fish stocks through overfishing and habitat destruction.

In 1992 our Northern Cod fishery collapsed to 1% of historical levels. Overfishing and irresponsible government decision-making in the face of scientific advice, led to the collapse. Cod stocks have never fully recovered. We don’t appear to have learned a lesson as we continue to over-exploit marine resources.

We are now bumping up against many of our oceans’ limits, and unless we speak up much more loudly about about greenhouse gas reductions, we will be like the frog in the pot of water, not noticing the water heating up until it’s too late.

Wayne Poole lives in Dundas.