by K. Richard, Nov 16, 2023 in NotricksZone
The timing of the dramatic Antarctic sea ice decline during the last deglaciation suggests solar forcing and sea ice retreat “instigated” century-scale climate warming and atmospheric CO2 change. This would appear to challenge the perception CO2 plays a causal role in glacial-interglacial sea ice and climate changes.
From ~21,000 to 19,500 years ago, when CO2 was thought to have been at its lowest point in the Quaternary ice age (~180 ppm), the sea ice surrounding East and West Antarctica completed 50% of its eventual deglaciation-era decline (Sadatzki et al., 2023).
“[I]ndependent lines of evidence supporting that early sea ice and surface ocean changes in the Southern Ocean initiated as early as ~19.5 ka ago (with signs of summer sea ice retreat in our reconstruction as early as ~21 ka ago) and thus (at least) about 2 ka before major deglacial changes in global ocean circulation, climate, and atmospheric CO2.”
The increase in 65°S insolation during these millennia was deemed sufficient to drive this magnitude of sea ice retreat.
“This early increase in local integrated summer insolation at 65°S, which is independent of the longitude, may have thus provided enough energy to initiate melting of the near-perennial sea ice cover in late glacial.”
by K. Richard, Nov 6, 2023 in NoTricksZone
Significant 21st century cooling in the Central Pacific, Eastern Pacific, and nearly all of Antarctica “implies substantial uncertainties in future temperature projections of CMIP6 models.” – Zhang et al., 2023
New research indicates West Antarctica’s mean annual surface temperatures cooled by more than -1.8°C (-0.93°C per decade) from 1999-2018. In spring, the West Antarctic Ice Sheet (WAIS) cooling rate reached -1.84°C per decade.
Not only has the WAIS undergone significant cooling in the last two decades, most of the continent also cooled by more than 1°C. See, for example, the ~1°C per decade cooling trend for East Antarctica (2000 to 2018) shown in Fig. ES1.
Of 28 CMIP6 models, none captured a cooling trend – especially of this amplitude – for this region. This modeling failure “implies substantial uncertainties in future temperature projections of CMIP6 models.
The post-1999 cooling trend has not just been confined to Antarctica. Sea surface temperatures (SSTs) in the Eastern and Central Pacific (south of 25°N) also cooled from 1999-2018 relative to 1979-1997. This cooling encompasses nearly half of the Southern Hemisphere’s SSTs.
by Dr. M. Wielicki, Oct 19 2023 in Climate ChangeDispatch
Antarctica presented a more complex picture. While the continent as a whole lost about 130 gigatons of ice each year during a similar timeframe, the loss was most pronounced in West Antarctica, especially around the Amundsen Sea sector.
This accelerated melting in West Antarctica is a matter of particular concern for researchers, as it is claimed to have the potential to destabilize larger sections of the Antarctic ice sheet, leading to more pronounced sea-level rise in the future.
Mass change of the Antarctic Ice Sheet from April 2002 to September 2020. Time series of mass change from the GRACE and GRACE-FO missions, M(t), for the entire Antarctic Ice Sheet (green) and its division into East Antarctica (blue), West Antarctica (red), and the Antarctic Peninsula (yellow). The vertical lines indicate the end of the GRACE and the beginning of the GRACE-FO monthly data availability (June 2017 and July 2018, respectively). Shadings represent 1-σuncertainties. Equivalent sea-level contribution (right axis) is approximated as 1 mm sea-level rise for 360 Gt of ice mass loss. Source
However, since early 2020, nearly 1,000 gigatons of ice have been added to Antarctica. This remarkable ice gain represents nearly one-third of the total ice loss since 2002.