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 21st 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.