2024 Annual Meeting of American Geophysical Union, Poster Session: GC11G: Advances in Climate Engineering Science, Washinton DC, 9 December 2024, Abstract:

Geoengineering Proposal to Leverage Earth’s Natural Cooling Mechanism

Earth’s natural mechanism of ice age cooling may be leveraged to mitigate anthropogenic warming. Evidence presented shows that this mechanism is a distinct form of equatorially symmetric La Niña (ESLN) in which the equatorial Undercurrent (EUC) surfaces and a winter monsoon cell forms over the equator. Diverging dry subsided air draws latent heat from the rising branches of the then divided Hadley cells, reducing tropical water vapor production, the dominant greenhouse gas. This idea follows Mark Cane’s Tropical Hypothesis of ice age forcing.

ESLN occurred naturally in 1998, when upwelled iron and nutrient rich EUC water caused a plankton bloom that spanned ¼ of Earth’s circumference. Increased ice age carbonate sedimentation in the equatorial Pacific is evidence of glacial ESLN.

The unique 1998 ESLN was in sequence with the precursor extreme 1997 El Niño, both amplified by previously unrecognized internal tide resonance (ITR). ITR follows very low amplitude cycles in the strength of equinoctial tides when the moon is also in low declination around eclipses. It emerges in the low density gradient pycnostad below the EUC, where incrementally increased tidal mixing lowers the local buoyancy frequency (N) to resonance with semidiurnal tidal forcing.

I propose a passive “trough drogue” array that leverages EUC kinetic energy to the same end, see figure. Internal waves build by sequentially slowing the trough segment of orbital water particle paths. The array’s 20 km width is the same as the present concentration of equatorial upwelling. A suitable location is at 174°E where the EUC flows through the Gilbert Islands. Once ESLN is established, diverging surface winds in the winter monsoon will power increased upwelling that amplifies its exchange of thermal potential. Given this persistent feedback, and eastward advection of low N waters, the required length of the array may be less than 100 km. Individual array elements will be controllably ballasted to sink below the EUC shear layer to turn the device off as needed.

The practicality of this idea depends upon the enormous addressable kinetic energy of the EUC, which is orders of magnitude greater than the incremental increase in tidal energy around equinoctial eclipses, from which ITR naturally emerges.

The following paper presented the hypothesis that Equatorially Symetric La Niña (ESLN) is the natural mechaism of global cooling that paced the Pleistocene ice ages:

The tropical hypothesis revisited: Is Pacific countercurrent consolidation the common mechanism of global cooling in interannual, millennial, and orbital time scales? John H. Duke, 4-11-2011, revision to: Climate of the Past Discussions, 6, 905-961, 2010 .

The objective of the above trough drogue array is to controllably create ESLN.

In the above hypothesis, orbital timescale ESLN forcing is by the combined effects of precession and obliquity cycles. The precession cycle is the average 21,000 year progression of the equinoxes around the calendar, which periodically shifts the Intertropical Convergence Zone (ITCZ) to the equator, a necessary conditoin for ESLN. Obliquity is the 41,000 year cycle in Earth’s tilt angle, which changes the declination of sun and moon on the equator at the solstice, and therby modulates the strengtgh of low latitude tide. Stronger tide excites internal tide resonanace (ITR) below the Equatorial Undercurrent and within the North Equatorial Countercurrent, evidently also a necessary conditoin for ESLN . Ice age ESLN requires both the combination of an ITCZ is shifted south and ITR.

Required obliquity:precession commensurability explains the remaining puzzle of the mid-Peistocene transition from 40 kyr to average 100 kyr ice ages. Due to changes in the period of precession, this is when the ratio between them changed from 1:2 (40 kyr) to either 2:5 (80 kyr) or 3:5 (120 kyr). Dual obliquity:precession forcing also explains Earth’s less humid climate following the “altithermal” 6,000 years ago, when a precessional ice age tendency (southward ITCZ migration) was forestalled by high obliquity angle (limiting ITR). This was the climate from which human civilization emerged.

Emergence of ESLN in 1998 was preconditioned by the extreme 1997 El Niño. ITR was present in both. This observational study shows the widely unregognized role of natural ITR in 1997 and the subsequent extreme 2015 event: Internal Tide Resonance in El Niño Amplification Duke & Werntz 2024. El Niño intensification in 1997 and 2015 was coincident with slightly increased but unique tidal forcing around the 18 year return of low declination tidal forcing in equinoctial eclipse seasons. These unconventionally unsmoothed data may revise longstanding understanding of El Niño.

Gregg et al. (1985) describe EUC shear: “Mixing in this zone resembles a sharply tuned harmonic oscillator, which can have large output changes for small forcing perturbations.” Accordingly, the above paper shows that the El Niño dynamic is responsive to a signal as weak as equinoctial eclipses. This encourages the potential of an engineered climate intervention that harnesses available and addressable kinetric energy in the EUC to induce similar internal waves in a 20 km band over the equator.

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PDF of the above 2024 AGU abstract submission: Geoengineering Proposal to Leverage Earth’s Natural Cooling Mechanism

2008 EGU abstract: A proposal to force vertical mixing of the Pacific Equatorial Undercurrent to create a system of equatorially trapped coupled convection that counteracts global warming

World Climate Research Program 2011 conference poster presents the hypothesis that tidal forcing is the common mechanism of global cooling in interannual, millennial, and orbital time scales: DUKE POSTER 2011 WCRP conference .