This is my fourth and final post on the 2021 report: Climate Change: The Physical Science Basis by the United Nations International Panel on Climate Change. I promised four posts covering ocean warming, sea level rise, salinity changes, and finally the subject of this post – ocean acidification. Acidification sounds scary doesn’t it? You might imagine a big rolling sea of water that can burn your skin off. It’s not that bad, but it’s still somewhat frightening. Now I don’t mean to scare people through my blog, that’s big media’s business. I want to inform people who don’t have the time to read thousands of pages of scientific documents about their contents. My blog posts are designed to provide you with a nuts and bolts synopsis of critical water issues plaguing the world today. But sometimes the data can be pretty worrisome.

So let’s get the scary bit out of the way shall we. The IPCC report points to the oceans absorption of carbon dioxide since the 1980s as being in the range of 20 to 30 percent of all human carbon emissions. As a consequence the pH of the ocean surface has declined 0.017 to 0.027 units per decade since the 1980s and subsurface pH up to a mile in depth have declined by 0.003 to 0.026. If you want to know more about how carbon dioxide impacts ocean pH you can find it here https://waterblogger.org/general-information/ocean-acidification-climate-change/ .

You may be asking yourself why such a small decline in pH is so scary. We have to do some chemistry to explain. As the ocean water absorbs carbon dioxide from the air a chemical exchange occurs, producing carbonic acid – H₂CO₃. The carbonic acid dissociates, generating HCO₃ and H⁺. What this means is that carbonate ions (CO₃) in the water are decreased and bicarbonate (HCO₃) ions are increased. It basically changes the whole carbonate chemistry of the ocean. You might not care but all the little critters that make their shells from calcium and carbonate in the ocean’s water do.  Calcium carbonate saturation rates of seawater have been declining at rates of 0.07 to 0.12 per decade.

What I find particularly fascinating in the 2021 IPCC report though is the variation in pH decrease that has been measured in different parts of the ocean now, for example the tropical Pacific Ocean is decreasing in pH at a greater momentum than other ocean areas, while the western tropical Pacific Ocean (renowned for its warm pool of water) shows slower pH declines. Coastal areas are acidifying at a greater rate than elsewhere as waters there are supersaturated with carbon dioxide. What’s happening at depth is interesting too. The well known meridional overturning circulation zones, such as the one in the Atlantic Ocean characterized by the Gulf Stream, bring warm water from the lower latitudes into the Polar Regions where it cools and sinks thereby producing acidification in the deep ocean. Areas like the subpolar North Atlantic Ocean and the Southern Ocean have the highest acidification found at depths greater 2 miles.

Governments are busy trying to decrease carbon dioxide emissions. The results will reverse ocean acidification at the surface, but not at depth due to the long time scales of ocean turnover. This will result in a lasting legacy in the deep ocean and impact biological resources for thousands of years to come.

Ocean salinity is not a topic people often think about when it comes to climate change. After all why in the world would the salinity of the oceans change just because human produced greenhouse gases like carbon dioxide are accumulating in the atmosphere and the ocean? There’s a simple answer to this question though and I explained it in a detailed blog post about six years ago. You can read it at your leisure ( https://waterblogger.org/general-information/ocean-salinity-climate-change/  ). The short answer for the sake of brevity in this post is that greenhouse gases are causing the atmosphere to warm and warm air holds more moisture resulting in increased rainfall. If the amount of rain exceeds the amount of evaporation then a body of water becomes fresher and if there’s more evaporation than rain the water becomes more saline.

 This is all measurable and scientists have been measuring atmospheric water vapor since the 1970’s. It is raining more over the Pacific Ocean where there is already a lot of warmth with accompanying atmospheric moisture and it is raining less in the mid latitudes of the Atlantic Ocean. The Pacific Ocean is becoming less salty and the Atlantic Ocean saltier. Scientists in fact have been measuring the very dickens out of the oceans saline content. There are measurements through the Soil Moisture and Ocean Salinity (SMOS) satellite system and ARGO’s 2000 plus ocean based floating instruments. The latest 2021 International Panel on Climate Change report entitled Climate Change: The Physical Science Basis indicates that between 1950 and 2019 trends in near surface ocean waters have shown strengthening of the contrast between high and low salinity areas of the ocean. The report quantifies the increase in contrast as 0.14 parts per thousand. This is up slightly from the 0.13 parts per thousand reported in the 2013 IPCC report of the same name.

So what if some parts of the ocean are getting saltier and others are getting fresher? Who cares? Well scientists are concerned that changes in salinity will affect the density of ocean water as higher saline content results in denser water while fresher water is less dense. Ocean density is already being impacted by temperature changes. Cold water is denser than warm water. Certain deep water circulation patterns in the oceans are dependent on dense surface water sinking in the polar regions, for example the Atlantic Meridional Overturning Circulation (AMOC). AMOC brings warm surface water from the equatorial region of the Atlantic Ocean to the northern Atlantic where it cools, sinks and is transported back towards the equator. It’s like a big conveyor belt in the ocean. Scientists say that AMOC impacts the climate of the Northern Hemisphere but they seem quite uncertain as to how. They suspect it keeps conditions a lot warmer in the Northern Hemisphere than it would otherwise be. But all they really know is what is measurable and what is measurable is that AMOC is weakening. This makes sense if polar waters are warming and denser saline waters in the middle latitudes of the Atlantic are not being transported to the poles breaking the chain of the Atlantic Ocean circulation. If you live on the east coast of the United States you are probably familiar with AMOC as it includes the Gulf Stream which moves warm water from the Gulf of Mexico along the coast of the United States and Canada then on up to the Northern Scandinavian countries. Scientists are also uncertain as to what exactly is going to be the result of a weakening AMOC. There is of course a lot of speculation by researchers often based on what occurred in the geologic past when AMOC weakened. The IPCC report though does not take a position on the veracity of the various studies purporting to know exactly what happened when AMOC weakened in the past nor are they even a hundred percent sure if the weakening of AMOC is being caused by climate change. The IPCC report says that the record is too short to determine if weakening of AMOC is natural variability or driven by climate change. So I won’t speculate either, I’ll leave that to the popular press.

I wrote my first blog post on ocean warming in 2016 (https://waterblogger.org/general-information/increase-in-ocean-temperatures-climate-change/). Almost six years have passed so let’s take a look at the state of the science in determining how our planet’s oceans are responding to the additional heat being transferred to them from the atmosphere. Conveniently the latest report from the International Panel on Climate Change (IPCC) just came out in 2021. It is entitled Climate Change 2021: The Physical Science Basis and is written in a much different style than the last IPCC report of the same name issued in 2013, because the science of climate change has grown. There’s a lot more certainty among scientists about what green house gas emissions from human activities are doing to our planet because there has been substantial data collection from a global network of monitoring systems over the last decade. Even the climate models have been updated and the predictions are now more useful. The bulk of the 2021 IPCC report is geared toward risk. In other words what is going to happen to this planet if it continues to warm and more importantly to readers of this blog, what is going to happen to the oceans?

The report uses a period between 1850 and 1900 as a reference period for comparison to today’s temperatures. You may recall those years were the beginning of industrialization. Scientists can now say definitively that global surface temperatures in 2021 are 2.1 degrees Fahrenheit higher than the time between 1850 and 1900.    

I wrote about ARGO in my very first post on how warming is affecting the oceans (https://waterblogger.org/general-information/oceans-and-climate-change/  ). ARGO is a system of floating scientific instrumentation deployed in the oceans around the world. The instruments measure, among other things, ocean temperature. The array of monitors has helped scientists determine the ongoing increases in ocean heat content in at least the upper 6500 feet of the ocean where measurements are being taken. Below 6500 feet there’s just not much data. But in the upper 6500 feet things are really warming up because these are the ocean depths where the ocean is storing heat from the atmosphere. Back in 2013 studies estimated that 90 % of earth’s energy caused by global warming since the 1970s is being stored in the ocean. New calculations say 91 %. Not much change there, but ARGO has been able to further refine for climate scientists where among the various depths of the ocean heat storage is concentrated. As you can imagine the first 3000 feet of the ocean is taking the big brunt of the action with 61 % of the total. This is important to realize because mixing and transfer of heat among the ocean layers is very slow. Later on in this blog post I’ll tell you why this is so important, but first a few more facts and figures for you from the report.

As everyone knows by now the three main greenhouse gases that are drivers of climate change are carbon dioxide, methane, and nitrous oxide. Carbon dioxide, which is in large part responsible for warming temperatures, is being exchanged and buffered by the ocean. Buffering is when carbon dioxide interchanges chemically with the water at the ocean’s surface to form a new compound – a weak carbonic acid. The ocean is taking up not only most of the heat from the atmosphere but is at the same time storing and reducing the amount of carbon dioxide. Carbon dioxide increases have been measured to be about 1.56 ppm a year over the last 61 years. During this time the accumulation of carbon dioxide in the atmosphere has remained about the same – 44 %. Why? Because the carbon is being taken up by the oceans and by the plants and soils of the planet. The circulation within the ocean slowly moves the carbon from the surface into deeper parts of the ocean.   

Scientists measure carbon in PgC. One PgC is equal to a billion metric tons of carbon. That’s a lot. The calculation of the cumulative amount of carbon dioxide from human activities that has been stored in the ocean is about 105 PgC. Do the math. Total human emissions of carbon dioxide are estimated to be 450 PgC. So the ocean is taking up 23 %. The fascinating thing that has been calculated in the 2021 IPCC report is when exactly the ocean will lose its buffering capacity for carbon dioxide. This is a mere chemical calculation, nothing special. Here’s the result: the ocean should be able to uptake carbon dioxide from the atmosphere through 2100, but its capacity to buffer will start decreasing around 2050.

What does this mean? It means that more carbon dioxide will remain in the atmosphere. For decades half of carbon dioxide has been taken up by the ocean and terrestrial carbon sinks and has slowed warming of the atmosphere. In 2050 the atmospheric temperatures will start to rise. You think its hot now, just wait.

And for the oceans? Average ocean temperatures today have increased by 1.6 degrees Fahrenheit from the reference period of 1850 to 1900. Since the 1970s, heat transfer to the oceans has increased by 0.28 – 0.55 yotta joules. No that’s not lotta joules; it’s yotta joules. Although it seems like a lot of joules to me. This a very large number, greater even than my calculator can handle. Take 0.28 and add 24 zeroes behind it. The 2021 IPCC report estimates that in the future ocean heat is likely to increase by 2 to 4 times that amount and 83 % of the ocean surface will warm over the 21^st century. And here is what I told you earlier that I’d reveal later in this post. Even if green house gas emissions are drastically cut back, ocean warming will continue until 2300 because of the slow circulation between the upper and lower ocean depths.

So there you have it, the dystopian future of the oceans is sealed.

            Gyzzzzlbex looks around and says, “Hey Azzterixx I don’t remember all this water covering up the city. I know it’s been two hundred years since we last visited this planet, but I’m sure there wasn’t this much water here then.”

            Azzterixx replies, “And where are all the people? I didn’t see a soul when we were on the way down here in our space ship. This planet was heavily populated when we last visited.”

            “Maybe they killed themselves off with those nuclear bombs they were testing in the desert when we had that hard landing in Roswell, New Mexico.”

            “Nah,” says Azzterixx, “My monitor doesn’t show any radiation.”

            “Well maybe there’s something here in the United Nations headquarters that will tell us what happened.”

            The two aliens look around in the various rooms and find a library.

            Azzterixx picks up a weighty tome, browses through it, then says, “Well look here Gyzzzzlbex, this document says that it is unequivocal that humans have warmed the atmosphere, ocean and land of this planet through release of green house gases and that there have been widespread and rapid changes to the atmosphere, oceans, cryosphere and biosphere as a result.”

            Gyzzzzlbex walks over to where Azzterixx is standing and tries to read over his shoulder. “What is that big book you are quoting from?”

            Azzterixx says, “It’s called Climate Change 2021: The Physical Science Basis. It’s by some panel of experts here at the United Nations called the International Panel on Climate Change. And holy cow it is 4000 pages long.”

            Gyzzzzlbex says, “How about turning the page there Azzterixx.”

            Azzterixx does so and they both inhale sharply.

            “So that’s what killed them all,” says Gyzzzzlbex.

            “Yes and they calculated it all out in this report. Amazing. They knew if they didn’t drastically cut green house gas emissions that the global surface atmospheric temperature could rise by as much as 12 degrees Fahrenheit by 2100. How sad. Well I guess our mission here is done.”

            As the aliens turn to leave Gyzzzzlbex says, “I wonder why they did nothing to stop green house gas emissions, knowing what they did?”

            I wonder too. I read the news coverage of the recent United Nations Climate Summit in Scotland which reported of a consensus among scientists and environmental organizations that the agreement reached there by some 200 countries will not be enough to mitigate greenhouse gases impacts on our climate. It’s been since January 2016 that I’ve written anything on how climate change is impacting the oceans, so I thought I’d take a hard look at the scientific research presented by the IPCC report on Climate Change: The Physical Science Basis just issued in 2021 versus the report by the same name from 2014. I wrote four posts on climate change in 2016 that covered:  ocean temperature changes, sea level rise, and ocean salinity. So I’m going to follow that process again in this blog to let long time readers catch up with the current science. Here is a link to the first post I wrote in 2016 (https://waterblogger.org/general-information/oceans-and-climate-change/ ).