Parametric Study of Prompt Methane Release Impacts III: AOGCM Results
Which Respect Historical PIOMAS Measurements
Abstract
Of immediate widespread concern is the accelerating transition from
Holocene-like weather patterns to unknown, and likely unstable,
Anthropocene patterns. A fell example is irreversible Arctic phase
change. It is not clear if existing AOGCMs are adequate to model
anticipated global impacts in detail; however, the GISS ModelE AOGCM can
be used to locally compare and extend the PIOMAS Arctic ocean historical
ice-volume dataset into the near future. Arctic Amplification (AA)
mechanisms are poorly understood; to enable timely results, a simple
linear, Arctic TOA grid-boundary energy-input is used to enforce AA,
avoiding the perils of arbitrary modification of relatively well-studied
parameterizations (e.g., restriction of cloud-top height to induce local
warming). Only PIOMAS springtime/max and fall/min Arctic ice-volume
decadal, linear trends were enforced. This temporally-broad
grid-boundary modification produces a surprisingly detailed consonance
with 10 out of 12 temporal profiles falling within 1-sigma of PIOMAS
temporal data for the entire history modeled (2003 to 2021). The data
are then integrated to 2050. The result is a zero-ice-volume,
summer/fall half-year, beginning ca. 2035 (onset 1-sigma of ±
~5 years), with mean annual Arctic temperatures
increasingly trending above freezing. Persistent, Arctic phase change
follows this half-year transition about 20 years later. Also present in
later stages, the 500 hPa height minimum is no longer nearly-coincident
with the pole, suggesting jet stream disruption and its consequences.
Hypothesized large clathrate-methane releases likely associated with
Arctic temperature and phase change are also examined. A basic
assumption is that the Arctic ice (i.e., temperature) must be preserved
at all costs. This work establishes a reasonably detailed timeline for
the Arctic phase change based on well-studied AOGCM physics, slightly
tuned to decades of PIOMAS data. This result also points to the Arctic
as a key, near-term site for localized, nondestructive intervention to
mitigate Arctic phase change (e.g., Stjern [2018]), thereby slowing
the Holocene -> Anthropocene growing-season disruption.
Although such an intervention cannot itself accomplish the requirements
of the IPCC SP-15 [2018], nor Planetary Boundaries theory, delaying
the Arctic phase change will likely extend the time-window for
accomplishing those critical tasks and ultimately to at least slow the
rate of increase of climate emergencies.