The oceans contain about 1.3 billion cubic kilometers of water, covering over 70% of the Earth’s surface. With such a vast amount of water, it may seem impossible for us to ever run out. However, while the total quantity of water in the oceans is enormous, much of it is not usable or accessible for human needs. Factors like pollution, overfishing, climate change, and population growth are putting increasing pressure on our ocean resources. So while we cannot technically use up all the water in the oceans, we can dramatically reduce the quality and quantity of the resources they provide if we are not careful.
How much water is in the ocean?
As mentioned, the oceans contain about 1.3 billion cubic kilometers of water. To put that number in perspective:
- If the Earth was smooth and all the ocean water was spread evenly across the surface, it would form a layer 2.7 kilometers thick.
- The volume of the oceans is approximately 1.3 billion cubic kilometers, which is enough to fill a cube 1,367 kilometers wide, tall and deep.
- If we took all the water on Earth – in the oceans, ice caps, lakes, rivers, groundwater etc – there is an estimated 1.5 billion cubic kilometers total.
- So the oceans contain around 96.5% of all the water on Earth.
Clearly there is an immense amount of water contained in the oceans. However, the critical question is how much of that water is actually available and useful for human purposes.
How much ocean water can we use?
While the oceans may seem boundless, there are many limitations on how much seawater is usable:
- Most of the ocean is too salty for human consumption or agriculture. Removing the salt requires desalination, which is expensive and energy-intensive.
- Much of the water is too deep or remote to access economically. Desalination plants are generally built along coastlines.
- Oceans absorb carbon dioxide from the atmosphere. Increasing ocean acidity makes it more difficult for seashells, coral reefs and some species to form their calcium carbonate shells or skeletons.
- Runoff of fertilizers into the oceans causes algal blooms and dead zones with low oxygen levels where marine life cannot survive.
- Oil spills, plastic pollution, sewage, chemicals, pesticides and industrial waste harm water quality.
- Overfishing depletes fish populations and disrupts the broader food chain and ecosystem.
These factors mean that while total ocean water supplies are vast, the amount that is usable is much more limited.
Is the available water decreasing?
Not only is usable ocean water limited to begin with, but several trends indicate the amount of usable water is declining:
- Global populations are increasing, especially along coastlines, putting more pressure on ocean resources.
- Climate change is causing ocean warming, rising seas levels, and more extreme weather.
- Increased carbon emissions leads to ocean acidification.
- Runoff of pollutants into the oceans is increasing with agriculture, industry, and populations.
- Overfishing removes billions of kilograms of fish each year beyond sustainable levels.
These factors reduce the productivity and health of ocean ecosystems. For example, up to a 40% decline in ocean phytoplankton has been linked to ocean warming and acidification over the past century. Phytoplankton are microscopic organisms that are the foundation of the marine food web. Their decline ripples throughout the ecosystem.
Is the decrease in usable water significant?
The reduction in usable ocean water is likely to have substantial detrimental effects for humanity, such as:
- Declining food security – Seafood provides 3 billion people with at least 20% of their average per capita animal protein intake. Overfishing and ecosystem changes put this food source at risk.
- Impacts on the global climate – The oceans currently absorb over 90% of the excess heat trapped by greenhouse gases and 30% of human-caused carbon dioxide emissions. Ocean ecosystem damage reduces these absorption capacities.
- Reduced coastal protection – Coral reefs, mangroves and coastal wetlands help defend shorelines from storms and erosion. Their degradation leaves coastal populations more vulnerable.
- Economic losses – Ocean resources directly contribute hundreds of billions of dollars to the global economy through tourism, fishing, trade, and more. Declining ocean health threatens these industries.
So while we cannot technically use up all the water in the oceans, the social, economic and environmental consequences of decreasing quantities of usable ocean water could be severe.
Can we reverse the trends?
There are concerted efforts underway to try and reverse the trends of ocean resource decline, but success is not guaranteed:
- International agreements aim to reduce overfishing and whaling through catch limits and moratoriums.
- Global initiatives strive to reduce agricultural runoff and increase sustainable practices.
- Many countries are expanding Marine Protected Areas to allow ecosystems to recover.
- Some nations are reducing plastic use and increasing recycling to limit ocean waste.
- Research is exploring coral reef restoration, fish population renewal, and phytoplankton enhancement.
- Individuals can help by reducing energy use, cutting unnecessary plastic consumption, and pressuring governments and corporations to take action.
However, the scale of the challenges is enormous. Successfully restoring ocean health will require major commitments and coordinated efforts from governments, businesses, organizations and individuals around the world. Even with strong action today, substantial damage has already occurred and some losses may be irreversible.
Conclusion
Given the massive total volume of water in the oceans, it is not possible for humanity to technically use it all up. However, through pollution, climate change, overuse and other factors, we can dramatically reduce the quantity and quality of the ocean resources available to us. While efforts are underway to reverse the trends, significant damage has already occurred. Successfully restoring ocean ecosystems and usable water supplies will require major global commitments. If humanity fails to make these commitments, we face the loss of essential services oceans provide, including food, economic value, climate regulation, and coastal protection. So in effect, while we cannot use all the water in the oceans, our actions and choices can “use up” many of the critical resources and support systems the oceans provide us. The future health of humanity is deeply intertwined with the future health of our oceans.