Ocean Acidification

Coral bleaching. Coral dies due to global warming and climate change. Image: Richard Carey - stock.adobe.com.

Ocean acidification is an issue that is sometimes left off the table when speaking about climate change, but it is becoming a growing global problem that could affect marine ecosystems and all of us. It is caused by an increasing amount of carbon dioxide (CO2) in the earth's atmosphere due to human activities.

How does this increase in atmospheric CO2 lead to more acidic oceans? The oceans act as a carbon sink in a variety of ways, absorbing approximately 30% of all atmospheric CO2 and 22 million tons a day (NOAA). CO2 dissolves when coming in contact with sea water, and there is also a biological pump that draws CO2 from the atmosphere. Photosynthetic plankton, algae, and other organisms cycle carbon through the ocean. This sounds great at a first glance - warming is being slowed, right?

While scientists at first thought this may be a good thing, in reality this ability for the oceans to absorb CO2 comes at a significant cost - changing seawater chemistry. As the oceans absorb more carbon, they become more acidic. Even though the oceans are vast, enough CO2 can have a significant impact. According to NOAA, atmospheric CO2 has risen steadily since the industrial revolution. During this time, the pH of surface ocean waters has fallen by 0.1. This means that the ocean has become more acidic (lower pH shows higher acidity, 7.0 pH is neutral, and higher pH is more basic). The pH scale is logarithmic, so this seemingly small change actually represents about a 30 percent increase in acidity. This is faster than any known change in ocean chemistry in the past 50 million years (Smithsonian Museum). And it likely won't stop there. NOAA states that "estimates of future carbon dioxide levels, based on business as usual emission scenarios, indicate that by the end of this century the surface waters of the ocean could be nearly 150 percent more acidic, resulting in a pH that the oceans haven’t experienced for more than 20 million years."

A graph displaying the levels of Carbon Dioxide (CO2) throughout the past 400,000 years. Image: NASA.

Why is this rise in acidity harmful exactly? Many chemical reactions that are central to life are sensitive to small changes in acidity. An example within our bodies is the pH of blood, which is within a range of 7.35 and 7.45. A small drop of blood pH (between 0.2-0.3) could lead to seizures, comas, and even death. A small change in seawater can have detrimental effects on marine life, impacting chemical communication, reproduction, and development.

The development of calcified skeletons in marine organisms is especially sensitive to changes in acidity. Acidic solutions have a higher concentration of Hydrogen (H+) ions in the water. These Hydrogen ions bond with carbonate, a molecule that is a critical component of calcium carbonate shells. Scientists from the Smithsonian Museum state that "the hydrogen essentially binds up the carbonate ions, making it harder for shelled animals to build their homes. Even if animals are able to build skeletons in more acidic water, they may have to spend more energy to do so, taking away resources from other activities like reproduction."

This is concerning because multiple studies have shown that many shelled organisms - such as krill and coral - play a crucial role in marine ecosystems and this may put them and the entire food web at risk. Many people rely on the oceans for their primary source of protein and other nutrients, and seafood is a large component of many countries' economies and job sources. Coral reefs also reel in a lot of tourism in tropical areas. As a result, we need to be considering our carbon footprint and finding ways to protect these shelled species.

A visual diagram of ocean acidification and its impacts on corals, other wildlife, and our economy.
Image: Navigating Nature.

This may seem like such a large and daunting problem....so what are some things that we can do personally about ocean acidification? There actually a lot of simple things you can do daily to help combat acidification. Some of these include:

Reduce your carbon footprint by conserving energy, walking or biking instead of driving, eating less meat, conserving water, buying products made locally, and buying less stuff.
Educate everyone you know - ask employers about their carbon footprints, make sure ocean acidification is on the agenda at Earth Day or environmental events, and talk about it in the classroom for presentations to educate your peers!
Get involved by joining campaigns and supporting organizations that actively do work to combat ocean acidification.
Influence government policy by voting in political leaders who care about environmental issues and who will advocate for legislation that could make a difference. You can also contact your current representatives to see if any legislation can be introduced or proposed - either just in your city or town, state, or even nationally!
Make smart consumer choices - refuse to use singe-use plastic bags and water bottles. Not only does plastic get in the oceans, but a lot of carbon and energy are used in the process of making them!
Continue to educate yourself and stay updated on what's going on!