Biogeosciences Research Spotlight

How Oceans Could Change If We Reverse Anthropogenic Warming

A computer simulation shows a net increase in primary production by phytoplankton if climate change were mitigated by 2200 but also indicates big changes in the makeup of those species.

Source: Geophysical Research Letters


It is well established at this point that anthropogenic factors are warming the planet at an unprecedented rate. Reducing and eventually eliminating our role in climate change is a lofty and necessary goal, but the planet’s climate—especially the oceans—carries an enormous amount of inertia. Here, using computer models, John et al. investigate how the oceans and the microscopic organisms that inhabit them would respond to a mitigation of anthropogenic warming over the course of about 100 years.

The properties of Earth’s oceans are the product of a complex balance of surface temperature, currents, biogeochemical processes, and numerous other factors. Warming and cooling of the climate influence each variable in unique ways, with some reacting quite quickly and others experiencing long lag times before any measurable response. These differences in inertia could lead to scenarios where the oceans’ properties continue to change for centuries or even millennia, even if anthropogenic warming could be mitigated entirely. To examine such a scenario and attempt to parse out these “legacy effects,” scientists simulated a 95-year period of warming (2006–2100) followed by a symmetrical period of cooling (2101–2195) and looked at how the oceans differed at the start and end point of the experiment period.

Overall, the team’s results show that net primary production by phytoplankton in the ocean is likely to rise in such a scenario. This increase in productivity is caused by increased mixing between layers of ocean water: As the planet cools, ocean waters near the surface respond faster than those deeper down. This results in a cooler top layer and relatively warmer waters between 400 and 800 meters depth. This, in turn, brings the density of the ocean’s layers closer together and allows for easier mixing. As the deep waters circulate more freely toward the surface, they carry new supplies of nitrate along with them, replenishing the vital nutrient that allows the phytoplankton to thrive. The magnitude of this effect varied considerably by geographic location, with the most extreme production increases occurring in the subtropics and Arctic.

The makeup of these phytoplankton populations, however, was quite different from contemporary norms. The models predicted a persistent depletion of silicates in the ocean waters, which allowed larger phytoplankton, especially the nondiatoms—which do not require silicates—to dominate.

The simulation results show that anthropogenic forcing will continue to influence Earth’s climate for a long time, even if it can be mitigated within the next hundred years. Understanding and predicting the future state of the planet should both prepare us for the future and serve as a reminder of the long-lasting impact our action today may have on the planet. Even if we find a way to completely stop anthropogenic warming today, the legacy effects of the change we’ve already caused would continue to echo many years into the future. (Geophysical Research Letters, doi:10.1002/2015GL066160, 2015)

—David Shultz, Freelance Writer

Citation: Shultz, D. (2016), How oceans could change if we reverse anthropogenic warming, Eos, 97, doi:10.1029/2016EO047305. Published on 4 March 2016.

© 2016. The authors. CC BY-NC 3.0
  • davidlaing

    Computer simulations are clever, but they are only as good as the hard data that back them up. Carbon dioxide doesn’t cause either global warming or ocean acidification. SOx and NOx do cause acidification, as evidenced by lower pH near coastlines. The oceans are well-buffered against possible pH changes due to CO2.

    • drklassen

      Yes, CO2 causes both warming and acidification.

      • davidlaing

        Sounds very authoritative, but can you back these statements up with hard data?

        • drklassen

          You first.

          • davidlaing

            The only positive correlations (which don’t imply causation) between atmospheric CO2 concentration and global temperature increase are those since the 1950s and those in the Vostok ice cores. The former are poorly correlated at best, and completely fail to explain the “hiatus” from 1998 to 2013 as well as the pre-1975 trend in temperature. The latter are well correlated on the increasing side, but with a huge lag of CO2 on the decreasing side, and close examination shows that both the increases and the decreases in temperature precede those in CO2, suggesting that the correlation shows rapid exsolution of CO2 from the oceans on heating and slow reabsorption of CO2 by the oceans on cooling (CO2 was well-dispersed in the atmosphere, hence the lag). The only actual experiment I’m aware of that tests the warming effect of CO2 was by Knut Angstrom in 1900, and his results were negative. A much more convincing cause of warming than CO2 is ozone depletion by chlorine and bromine emissions from large, non-explosive volcanoes, allowing increased irradiance by solar UV-B. All major warming events throughout geologic time have been coincident with major effusive (non-explosive), basaltic volcanism.

            • drklassen

              *Physics* tells us the CO2 is a greenhouse gas. Venus is a good proof-of-concept.

              There was no hiatus.

              That other feedbacks affect temperature is not proof that CO2 doesn’t affect it.

              • davidlaing

                No, but Angstrom did disprove CO2’s warming effect, and no one else has proved it correct.

                Venus isn’t hot because of CO2; it’s hot because it’s virtually spin-orbit coupled with Sun. It keeps the same hemisphere facing Sun all the time. Powerful winds distribute the heat over the entire planet.

                He said, she said. You can’t have it both ways. If there was no “hiatus,” as Karl et al. speciously claim, then global warming was much flatter than predicted by the climate models. The dramatic AGW from 1975 to 1998, BTW, was most likely caused by spray cans putting CFCs into the atmosphere. The CFCs broke down on PSCs, releasing chlorine, which depleted the ozone layer, as is well-documented. The great warming in 2014-15 was most likely caused by Iceland’s Bardarbunga volcano, the largest basaltic (non-explosive) eruption since Laki in 1783. Greenhouse warming is a tired old flawed theory, and it’s high time we put it to rest.

                • drklassen

                  And how does a volcano cause warming if not via GHGs?

                • davidlaing

                  Everyone understands that explosive volcanoes cause cooling by creating a veil of sulfuric acid in the lower stratosphere that increases Earth’s albedo. Few understand that non-explosive (i.e., effusive basaltic) volcanoes emit large quantities of HCl and HBr, which drift up into the stratosphere and deplete ozone catalytically, thereby increasing irradiance by solar UV-B, which is absorbed mainly by the oceans. UV-B is about 48 times as thermogenic as the CO2 that is most readily absorbed by CO2. Together, these two styles of volcanic eruption do a far better job of explaining major temperature swings throughout the Phanerozoic than does CO2.

                • drklassen

                  That’s not how volcanoes cool.

                  As for the rest, point me to the papers.

    • AndyG55

      Totally correct david. There is no mechanism whereby CO2 can cause atmospheric warming except in erroneous model assumptions.
      Ocean plant life uses the increased atmospheric CO2 just like land plant life does. Ocean acidification is a myth.