Burning fossil fuels is killing more ocean species than land species

Part I: Ocean Acidification


Around 1 million species are threatened with extinction due to human activities

March 2021  Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services

Ocean species are going extinct faster than terrestrial species due to ocean warming

April 2019  Nature


In the entire 4.5 billion year history of Earth only two living organisms —cyanobacteria and humans— have so completely altered the oceans, atmosphere, and land that all life on Earth was threatened with extinction at the time.

Cyanobacteria were the first photosynthesizers on an anoxic Earth, pumping oxygen into the oceans and atmosphere for more than 3 billion years (3.7 bya – 500 mya), killing nearly every other living thing because oxygen was toxic to all life on Earth at that time.

Humans have been doing it through water, air, and land pollution in a much more compressed time frame—only about 150 years—by burning fossil fuels while simultaneously eliminating natural carbon sinks through intense urbanization and bad land use policies, pumping massive amounts of CO2 and other greenhouse gases into the atmosphere and oceans causing ocean acidification and ocean warming.

In this two part blog, I discuss the science behind the title to show how humans burning fossils fuels is directly linked to the mass extinction of marine life through ocean acidification (Part I) and ocean warming (Part II).

Ocean Acidification

Ocean acidification is one reason ocean species are going extinct faster than terrestrial species. The ocean is 25-30% more acidic than it was 150 years ago as a direct result of CO2 released from burning fossil fuels since then. We know this from multiple independent lines of evidence looking into the deep past and from direct pH measurements over the last 150 years around the globe.

The oceans act as a buffer to excess CO2 in the atmosphere by dissolving it in seawater where the carbon becomes available to marine organisms that use it to make shells and skeletons. When those organisms die, they sink to the bottom of the ocean where that carbon remains stored for thousands of years, thus removing it from the surface of Earth. In other words, the oceans are the largest carbon sink on Earth.

Diagram of the fast carbon cycle showing the movement of carbon between land, atmosphere, and oceans in gigatons (1 billion tons) of carbon per year. Yellow numbers are natural fluxes, red numbers are human contributions, and white numbers (in parentheses) are stored carbon (total, not per year). The oceans are the largest carbon sink on Earth with more than 40,000 gigatons of stored carbon in the deep ocean and ocean bottom sediments—more than all other stored carbon pools combined. Diagram from NASA Earth Observatory.

When there is too much dissolved CO2 in the oceans, the excess combines with seawater to make carbonic acid and hydrogen ions, both of which increase acidity. Under acidic conditions, carboniferous shells and skeletons do not form properly so marine organisms who need them don’t survive. Ocean acidification also affects the formation of proteins, fertilization, and other critical cellular and developmental functions in most marine species, including plankton and other microbes at the base of marine food webs. The collapse of marine food webs triggers a domino effect on every species throughout the world’s oceans.

This is why so many marine species go extinct when the oceans are even slightly more acidic. And when it occurs this fast—25-30% in 150 years—marine species are going extinct at a faster rate because they don’t have time to adapt and evolve to rapid ocean acidification.

Illustration of ocean acidification and its effects on marine life and coastal communities. Illustration from Fisheries and Oceans Canada

Is this really happening from humans burning fossil fuels?

The rapid burning of fossil fuels is one of the more serious human activities for several reasons: think about all the time it took earth to make fossil fuels, which you can think of as stored carbon. It took more than a hundred million years to store all that carbon as organic plant and animal material, and another hundred million years to convert that organic material into a different form of stored carbon: fossil fuels (oil, coal, shale, natural gas, etc.). But it has only taken us about 150 years to release more than two hundred million years of stored carbon back into our atmosphere and oceans. The removal of natural carbon sinks through increased urbanization and bad agricultural methods has only exacerbated this issue because even more CO2 ends up in the oceans.

This graph from the National Oceanic and Atmospheric Administration best illustrates the difference between fossil fuel and volcanic sources of CO2 in the atmosphere. It shows CO2 emissions in billions of metric tons over time since 1750, which is the actual beginning of the Industrial Revolution with the invention of the coal-burning steam engine. The green line shows fossil fuel emissions and the purple line shows an annual average of volcanic emissions, another major source of CO2.

The annual average of CO2 emissions from volcanoes have remained consistently below 1 billion metric tons since 1750. CO2 emissions from fossil fuels was also low until around 1870—150 years ago—when burning of fossil fuels increased rapidly and accelerated to where we are today. 

CO2 emissions from volcanoes are still below 1 billion metric tons today, whereas CO2 emissions from burning fossil fuels are approaching 40 billion metric tons today, more than 40 times the CO2 emissions from volcanoes.

This graph, also from NOAA, shows how the increase in annual CO2 emissions from burning fossil fuels, the blue line with blue vertical scale on the right, directly corresponds with an increase in atmospheric CO2, the pink line with pink vertical scale on the left.

This graph clearly shows that the sharp increase in atmospheric CO2 since around 1870 is coming from burning fossil fuels.

In fact, we can look back 800,000 years using actual samples of atmosphere trapped as bubbles in Antarctic ice revealing the amount of atmospheric CO2 over a much longer time frame. This figure shows CO2 levels in parts per million, which is a different way to measure it from the previous two graphs, which were in billions of metric tons. 

The next figure shows that atmospheric CO2 levels have not been above about 300 parts per million for the last 800,000 years until around 1950, when global fossil fuel emissions really exploded.

I won’t go into the details of the next figure because it is fairly complicated, but using multiple lines of independent scientific evidence we know atmospheric CO2 concentrations going back at least 500 million years.

On April 3, 2021 scientists measured 421.21 parts per million CO2 in the atmosphere, the highest level in more than 3 million years. By 2050, it is estimated that we will be at 500 ppm, the highest level in more than 20 million years.

Based on all these independent lines of scientific evidence, scientific consensus is that ocean acidification and subsequent marine extinctions are really happening from humans burning fossil fuels, releasing very large amounts of CO2 into the atmosphere, which is then dissolved in seawater. The excess dissolved CO2 has made the oceans 25-30% more acidic in just 150 years. Acidic and warming oceans are killing marine species faster than terrestrial species because marine species have no way to escape these rapidly changing conditions.

This blog was adapted from a zoom presentation Michael Atkins gave on Earth Day 2021 with Saving Ocean Wildlife. Click here to watch the recording of that presentation called “The State of the Oceans: Past, Present, and Future

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