TCG Side Effects

More fish, More CO2 Sequestration,
Some Localized Weather Changes.

As is the case with other solar geoengineering (SG) concepts, Tropical Cloud Generation (TCG) does come with a couple of known side effects in addition to the primary design functions of mitigating cyclone formation and global warming.  Unlike other SG concepts, two of the known side effects of TCG would be extremely beneficial. These “side effects” may be sufficiently motivating to promote further investment and deployment of TCG beyond the minimum threshold needed to end large cyclone formation.

The two very clear side effects of positive note are:

1. Greatly increased local primary production (improved fisheries) in the regions of deep sea-surface mixing, and
2. Greatly increased CO2 uptake/sequestration in the regions of deep sea-surface mixing.

A third “side effect” is uncertain, and complex simulations (of a type not commonly done) will be needed to better clarify this issue: The storms and clouds around and downwind of the cool patch will have an effect on local weather patterns.  We’ll come back to that later, but the key word in this is “local”. Once greater clarity is achieved, these effects could be used to help targeting the regions of interest so that changes in the weather stay harmlessly out at sea. We’ll address the more certain and most promising “side effects” first.

Increased Primary Production.

 Without the upwellings and inflow from rivers there would be almost no net primary production.  About 25% of total marine fish catches come from five upwellings that occupy only 5% of the total ocean area.  The mixer-driven upwellings would feed the phytoplankton, which together with the mixing would oxygenate the waters at least down to the 1% light level (~300 m) and lead to them becoming highly productive fishing areas instead of ocean deserts, which currently cover >25% of the world’s oceans and are growing at the rate of 1-4%/yr.

Ocean waters much below the Mixing Layer Depth (MLD) – a mere 20 to 50 m in some of the targeted areas – have been steadily becoming more oxygen depleted, making it impossible for most fish to survive in these areas much below the MLD.  The proposed deep mixing could extend the MLD in these areas, ultimately to over 400 m, drive upwelling and increase the depth at which there is sufficient oxygen to support diverse fish species.

Ocean deserts (the blue areas in the above map) shouldn’t be confused with dead zones.  Dead zones form where large rivers (such as the Mississippi) discharge huge amounts of nitrates from agricultural runoff that overstimulate algae growth in the spring and summer, which then die, sink, and decompose.  Bacteria feeding on the algae consume the oxygen in the bottom waters causing most bottom-dwelling marine life (like shrimp) and many other fish to die.  These dead zones are generally in waters too shallow (as near Texas and Louisiana in the Gulf of Mexico) for a nuclear sea-mixer designed for tropical cloud generation to navigate, so Tropical Cloud Generation (TCG) wouldn’t help oxygenate those waters, though it could help cool them a little.

The patchy mixing by sea mixers in deep waters wouldn’t begin to overstimulate algae at sea.  It would just make it possible for green phytoplankton to thrive at the levels needed for healthy marine life. These biologically rich regions will remain filled with life for many years, and they will drift in the ocean currents, eventually coming near to land and becoming a welcome fishing bounty for the local fishing industries.

CO₂ Uptake and Sequestration

The expansion of the “biological deserts” is a global warming feedback mechanism – global warming is increasing the expanse of ocean deserts, where the concentration of phytoplankton is extremely low and little CO₂ is being taken in through the biological cycle.  This does not mean that the ocean is absorbing less CO₂.  The ocean carbon balance is comprised of multiple complex mechanisms, including: solubility and mixing (increasing ocean acidification), mineralization, demineralization, venting, and through the biological cycle centered in phytoplankton.  So as atmospheric CO₂ concentrations increase, the rate of uptake and sequestration into the oceans will likely continue to increase, and ocean acidification will increase, which will likely cause more stress for vital components of the ocean ecosystem (including some species of phytoplankton).  

Sinking organic particles constitute a primary source of energy for ocean ecosystems and a mechanism for carbon sequestration in the deep ocean.  While the larger organic particles (>100 mm) sink quickly (~100 m/day) they steadily fragment as they descend.  Micron-sized particles sink 10,000 times slower (300 m in a decade) and represent one of the bottlenecks in the rate of CO₂ sequestration by the ocean. 

It is important to point out that this portion of ocean sequestration – the gradual sedimentation of organic particles onto the sea floor – does not result in greater acidification of the ocean waters.  (Increased primary production may help alleviate the problem.)

            Ocean carbon uptake is a very complex issue, and extensive simulations and studies are needed before all the effects of increased mixing can be understood.  However, the local increase in primary production caused by the upwelling of deep waters alone should increase uptake of CO₂ in targeted areas.  Perhaps more significant will be the increase in atmospheric mixing very near the surface because of the increased local wind speeds from the convection generated by the cool patches in the warm seas. It is the surface wind speed and sea surface temperature that primarily determine surface CO2 uptake rate, together with the amount of dissolved organic matter in the top 0.1 mm of the sea surface. Another factor is rainfall, as the rain (at least for the past half-century) contains a much higher CO2 content (lower pH) than the ocean. The greatly increased local rainfall produced by TCG will increase ocean CO2 uptake in those regions.

The areas of interest – where the MLD is very shallow and the surface waters are extremely warm – currently have uptake values of near zero.  Using a Sea Mixer to create a local upwelling in those regions could increase the uptake level to the 2 mole-CO₂/m²/yr currently seen over parts of the sub-tropical southwestern Pacific where SST is below ~23 C.  If so, a single 60 km² diameter cool patch would see an increase in carbon uptake levels of >125 kt-CO₂/yr, an accelerated rate that would perpetuate for several years.  That could amount to each Sea Mixer in operation sequestering much more CO2 than the largest current Carbon Capture and Storage project in the world!

Localized Weather Changes

            Considerably more work needs to be done in order to better clarify the above two “side effects”, but in both cases those “side effects” are all but certain to be welcomed by all – more fish, and more ocean CO₂ uptake. 

            The third side effect is less certain to be universally positive: local weather changes due to the rain and storms caused by the cool patches.  While nearly everyone would welcome an increase in fish populations, some might not appreciate a change in the weather that would result in more clouds and rain that might last days at a time as the cool patch drifted past.  This would be especially true for tourist destinations, but it should be assumed to be true for most populations (though there could be humanitarian aid considerations for parched countries in West Africa and the Arabian Peninsula – though obviously that would be a matter of agreement and permission from all countries affected).

Global warming is changing and will increasingly change the weather in ways that are less desirable for most of the earth’s peoples:  more droughts in the subtropics, more rain in the higher latitudes, more severe urban heat waves, more extreme weather events everywhere. A recent study showed that SG implemented uniformly at the scale needed to offset half the warming expected from a doubling of CO₂ would dramatically reduce the undesirable weather effects from global warming for almost everyone. That study simply assumed the SG reduced the solar constant uniformly by 1%.

As the needed simulations are carried out, targets for patchy mixing could be chosen that are unlikely to cause unwelcome local weather changes while mitigating most of the undesirable effects that otherwise would come from global warming.  We offer a very brief review of the mechanics of cyclones, anticyclones and sea breeze-induced clouds and storms on our “Cyclones and Sea Breezes” page, but it is worth reiterating here:  A small anticyclone storm could only form in regions with very low mid-troposphere wind speeds.  Once formed, an anticyclone, would remain centered on the cool patch and could not move faster than the ocean currents – which are extremely slow and their movement is easy to forecast.  In regions that have even moderate winds, there would likely be fog over some of the cool patch and a train of clouds and rainstorms that would form and gradually disperse and rain out downwind, with the only severe storms occurring along the upwind boundary.  Like the anticyclone, these effects are caused by and tethered to the cool patch, which means they will be limited in their range of impacts, and those impacts will move in a very predictable and very slow path along with the ocean currents.

Therefore, care would have to be taken to look at prevailing wind patterns and the projected weather in regions where we would wish to generate a cold patch, and the position of the patch would have to be considered based on the effected range of the resultant cloud generation (along with the storms and rain) as the patch ambles along slowly in the ocean surface currents.

The positive impact of TCG on climate is producing shading fog and clouds, and convective heat transfer from the surrounding sea surfaces upward, where it radiates into space.  Whatever rain and clouds that are produced that travel overland reduce the efficiency of that goal.

But again, to be clear: additional work needs to be done to clarify the weather impacts of these cold patches.  The near-term goals would be to target the TCG effects well out to sea, where there is no direct interaction with land.