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Late Holocene ~350-450AD global warming and 2.5-metre sea-level rise driven by
the Sun not CO2: archaeological, geological and astrophysical literature synthesis
Dr Roger Higgs, Geoclastica Ltd, UK
Invited keynote lecture, modified abstract 14th June 2020
'3.Paleoklimat', 3rd Scientific Conference on 'Climate Change in the Geological Past'
Polish Geological Institute, Warsaw, 18-19th November 2020
The Intergovernmental Panel on Climate Change (IPCC) says the 30cm sea-level (SL)
rise measured since 1850AD must be due to warming by Man's CO2 emissions, as no
SL oscillation in the previous 2,000 years exceeded 25cm (only "medium confidence";
https://www.ipcc.ch/site/assets/uploads/2018/02/WG1AR5_Chapter05_FINAL.
pdf). This disregards dozens of publications since 1940 describing worldwide geo-
and archaeological SL benchmarks that jointly prove a SL rise of ~2.5 metres reaching
~1.5m above modern SL (corrected for subsidence/uplift), and a ~2m SL fall before
and after, all in the 1st Millennium AD. The 2.5m transgression has many local
names, e.g. Romano-British (UK), Lytham IX (UK), Dunkirk II (Belgium), St Firmin
(France), PTM-9 (Sweden), Gilbert V (Pacific) and Wulfert (USA); it is best-known as
'Rottnest transgression', from the famous Holocene interglacial global SL curve of
Fairbridge (1961), whose final version (1977) shows the Rottnest highstand loosely
(C14-) dated as ~350AD, the highest SL of the last 2,000 years. In tectonically stable
southern England, seaside Roman forts and Norman castles have SL benchmarks
(e.g. docks, water-wells) confirming the Rottnest transgression, and the pre- and
post-rise SL falls, and giving firmer dates (dendro, coins, pottery, documents). For
example, thanks to SL rise, Portchester fort (built ~300AD) was 'retrofitted' with a
tidal moat and a tide-flushed latrine by Normans ~1100AD. Meticulous excavations
show London is similarly a 1000yr 'SL dipstick', with impeccable evidence for two
oscillations (fall-rise-fall-rise) of high-spring-tide level (HSTL, proxy for mean SL):
~2m FALL 1 is based on: (A) successive Roman Londinium timber quays younging
from ~50 to ~250AD, stepping down 2m into the Thames estuary, and (B) the oldest
of these quays are behind the ~270AD Thames-side defensive city wall;
~2.5m RISE 1 (Rottnest), after 250AD, caused severe estuary-flow erosion of the
wall's front, reducing the original ~2.5m wall thickness by ~1m in places. A deep
(dm) notch straddles the wall's lower 1.3m. The notch's sharp top (probable
minimum HSTL) is 2.1m higher than the top of the ~250AD quay (add ~40cm for
HSTL freeboard). Proving the rise was well advanced just decades after wall
construction, a drainage culvert (tunnel) ~0.5m above the wall's base was
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deliberately plugged with rubble, including post-320 pre-400 pottery (a 2nd culvert
contains undated layered silt). Discussing this, one author supposed "the river level
could hardly have risen almost 2 m in half a century", evidently unaware of a proven
2 to 3m SL rise in decades in the previous interglacial.
~1.5m FALL 2, by 680AD, is indicated by a dendro-dated Saxon timber waterfront
revetment; its top (lowered by erosion, therefore ~HSTL) is 1.6m below the notch
top. A later Saxon ~1000AD jetty only ~0.2m higher than the revetment is associated
with a man-made foreshore rubble bank of blocks eroded from the wall (in stage 2);
>1.0m RISE 2, between 680 and 1150AD, is based on foreshore sand and gravel (12th
C pottery; no wall rubble) abutting the wall to 0.6m higher than the revetment.
The 2.5m rise agrees with Fairbridge's (1977) Rottnest 2.5m global mean SL rise. This
suggests London's tidal range did not change appreciably during the rise. The
notch's top is at +2.6m above Ordnance Datum (OD, = mean SL). This restores, given
1.5mm/yr subsidence (GPS, PSI), to +4.9m if the highstand was ~450AD (1,550yrs
subsidence). If the tidal range was the same as today (London Bridge 7m), and
reached the same +4m height relative to OD, London's 450AD mean SL restores to
0.9m (4.9 minus 4) above today's, very near Fairbridge's global +1.2m.
Further supporting the Rottnest rise's inferred ~350-450AD age and severity (~2.5m)
is the main exodus to Britain of Angles, Franks, Jutes and Saxons from 410 to 450AD
(documents, grave goods), abandoning their drowning NW Europe coastal-plain
raised villages (terpen). Thus the English nation originated by SL rise. No known
Dark Ages document mentions the SL rise (except perhaps the 'Groans of the
Britons; https://en.wikipedia.org/wiki/Groans_of_the_Britons), suggesting that for
literate peoples the 2.5cm/yr average rate (2.5m in 100yr), far from life-threatening,
excited little or no written comment. Oddly the immigrants avoided settling in
Londinium until the 7th C, despite its emptiness (Romans abandoned Britain ~410)
and easily defended walls. Instead they founded Lundenwic just 1km upstream. I
ascribe this 200yr occupation hiatus (cf. Anglo-Saxon homelands) to the Rottnest
HSTL, up the wall, denying early Saxons a place to beach their boats at high tide.
Fairbridge's curve shows other large rapid SL rises (1 to 5m in <200yr) from 4000BC
to 1000AD. Each highstand was brief (<100yr) and followed by a rapid SL fall (1 to
3m, <200yr). Only glacio-eustasy explains such rapid, metre-scale SL ups and
downs; glacio-isostasy causes slower one-way rise or fall, varying with latitude.
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What caused these 'Fairbridge-type' SL rises? By cross-matching graphs of global
temperature, SL and the Sun's activity since 4000BC, Fairbridge rises are seen to
correlate with global-warming events (from proxies, e.g. tree-ring widths, ice-core
oxygen isotopes), and to lag ~100yr behind solar Grand Maxima (GMs, 200-2,000yr
apart; from cosmogenic isotopes in tree rings and ice cores). This supports
Svensmark's theory of increases in the Sun's magnetic flux reducing cloudiness
(cosmic-ray link), boosting solar warming of the ocean, in turn warming the
atmosphere. The Rottnest rise and a coeval ~350-450AD global warming lagged
~100yr behind a 275 to 345 GM (peak at 310AD, unsurpassed until 1991). Estimating
the lag-time more exactly from graphs of post-1700 measured SL, temperature and
solar output, I find that SL inflections lag behind corresponding solar inflections by
50-25yr (decreasing since Little Ice Age), while temperature lags the Sun by 100-60yr
(decreasing). I attribute these lags respectively to ocean 'conveyor belt' circulation
and ocean thermal inertia (slow mixing). In this model, each Fairbridge SL rise is due
to GM 'overwarming' of Atlantic surface water (constantly downwelling in the N
Atlantic) which, decades later, upwells and circles Antarctica, melting the ice shelf,
unleashing an ice-sheet-rim collapse event (google MISI, MICI), launching a vast
iceberg melange, raising SL 2-5m in decades. Diverse Antarctic evidence suggests
such a collapse event in the last 5,000 years. Each SL rise ends by eventual arrival of
'normal' colder upwelling water, re-freezing the buttressing ice shelf, terminating
ice-sheet collapse and SL rise. Rapid, within decades, transition to SL fall reflects
(delayed) global cooling (by continued circulation and mixing of the post-GM colder
water, enhanced by the ice melange directly cooling the ocean and raising Earth's
albedo), raising the proportion of precipitation falling as snow (over a wider
latitudinal extent, raising albedo), causing SL to fall. The strongest GM in >2,000yr
has just ended (1937-2004; magnetic peak 1991), so I predict continued warming for a
few more decades and an imminent ~3m SL rise ending by 2100.
IPCC's 25cm claim (above) cites the 'corrected' Holocene SL curve of co-lead-author
Lambeck. But Lambeck's Earth-ice modelling rashly rejects all outlying single-point
benchmarks and is negated by the 'SL dipsticks', i.e. sites with multiple benchmarks,
very accurately dated and heighted, proving 1-to-3-metre oscillations, e.g. terpen,
forts and Londinium, all intermittently occupied through more than 1,000 years.
For sources of any of this information, please email rogerhiggs@hotmail.com