By Alex Kirby via Climate News Network
LONDON, 26 August – Researchers in Germany say the carbon dioxide that is absorbed by the world’s oceans may still be damaging the atmosphere – bizarrely, by amplifying the warming caused by the greenhouse gases which are there already.
They say this could be happening because the CO2 that enters the water is limiting the production of a gas, dimethylsulphide (DMS), which helps to cool the Earth. The gas helps clouds to become denser and reflect more sunlight back into space and so reduce overall warming.
Scientists are already concerned about the effects of CO2 on seawater because it is making the oceans more acidic and less friendly to many forms of marine life. They now think this growing acidity is also suppressing the production of DMS.
The research is one of the first suggestions that oceanic CO2 may be having a doubly harmful effect, by increasing both marine acidity and atmospheric warming – an example of what scientists call a positive feedback, when climate change in effect fuels itself.
But there are suggestions that there may be little cause for concern – because DMS production may perhaps depend more on the temperature of the water than its acidity, so the gas’s cooling potential could in fact increase. Because the seas are warmer, this argument runs, more DMS is created, and so some scientists believe it will balance the negative effect of increased acidity.
An international team of scientists at the Max Planck Institute for Meteorology (MPI-M) has published its research in the journal Nature Climate Change. They conclude: “Our results indicate that ocean acidification has the potential to exacerbate anthropogenic warming through a mechanism that is not considered at present in projections of future climate change.”
Fossil fuel burning releases over six billion tonnes of carbon into the atmosphere annually. These greenhouse gas emissions are certainly causing temperatures to rise, but the team says global warming is not the only threat from increased atmospheric CO2 concentrations.
Acidification, which occurs when CO2 in the atmosphere reacts with water to create carbonic acid, has already increased ocean acidity by 30% since the Industrial Revolution.
Accelerated Warming Possible
Depending on the extent of future CO2 emissions and other factors, the Intergovernmental Panel on Climate Change (IPCC) predicted in 2007 that ocean acidity could increase by 150% by 2100.
With the rise as well of atmospheric CO2 concentrations from the pre-industrial level of 280 parts per million to 400 ppm in 2013, the amount of carbon in the oceans has increased substantially and rapidly.
Global data collected over several decades show that the oceans have absorbed at least half of the anthropogenic CO2 emissions that have occurred since 1750.
When DMS enters the atmosphere it can form new aerosol particles that affect clouds’ albedo (their ability to reflect solar radiation back out into space) and so cool the Earth’s surface. If marine DMS emissions decline, this could reduce the cooling effect appreciably.
In a “moderate” scenario described by the IPCC, which assumes no reductions in greenhouse gas emissions, global average temperatures are expected to increase by between 2.1 and 4.4 °C by 2100.
Adding in the effects of acidification on DMS led the MPI-M researchers to calculate that there would be additional temperature increases ranging from 0.23 to 0.48°C.
Simply put, the researchers say, the research “shows that ocean acidification has the potential to speed up global warming considerably.”
21 Apr 2024 
