Arctic decadal and interdecadal variability
Polyakov and Johnson
Abstract:
Atmospheric and oceanic variability in the Arctic shows the existence of several oscillatory modes. The decadal-scale mode associated with the Arctic Oscillation (AO) and a low-frequency oscillation (LFO) with an approximate time scale of 60–80 years, dominate.
Both modes were positive in the 1990s, signifying a prolonged phase of anomalously low atmospheric sea level pressure and above normal surface air temperature in the central Arctic. Consistent with an enhanced cyclonic component, the arctic anticyclone was weakened and vorticity of winds became positive.
The rapid reduction of arctic ice thickness in the 1990s may be one manifestation of the intense atmosphere and ice cyclonic circulation regime due to the synchronous actions of the AO and LFO. Our results suggest that the decadal AO and multidecadal LFO drive large amplitude natural variability in the Arctic making detection of possible long-term trends induced by greenhouse gas warming most difficult.
In my view, you are reaching. I don’t see any data that specifically supports
but your links are quite technical (e.g., sea ice extent is not the same as ice mass).
I will note that your first reference starts the Introduction with
“Since the late 1970s, the Arctic sea-ice extent has exhibited a significant decline in all seasons, which is due to human influence (IPCC, 2021) and is expected to continue.”
I think that sea ice extent is actually more important than mass/volume. The sea ice extent (SIE) obviously affects albedo. It increases or decreases the ocean-heat flux to the atmosphere, changing temperature gradients and thus influencing large-scale wind flows. The halocline (the top 100+ meters of the ocean where the salinity varies rapidly) is also changed.
It’s not clear that there are any mulitidecadal oscillations. Michael Mann of hockey stick fame was a strong proponent of the existence of multidecadal oscillations. He published several papers doing statistical analysis of various climate datasets demonstrating their properties.
Then, in 2020 he published an article that contradicts his, and many others, previous work, claiming that multidecadal oscillations are a statistical artifact:
"Here we use a combination of observational data and state-of-the-art forced and control climate model simulations to demonstrate the absence of consistent evidence for decadal or longer-term internal oscillatory signals that are distinguishable from climatic noise. "
Lot’s of papers are still being published about the PDO and NAO, so I don’t know how much consensus there is around Mann’s conclusion that it’s all just noise.
Since there is no well-defined, agreed-upon preinstrumental AMO time series that could be. Model failure to find oscillations may be just that, model failures.
Stroeve et al. found a 60/40 split between external forcing and internal variability through 2011. Since then Arctic sea ice extent has continued to go sideways, so the unforced portion may be higher than 40%.
“Kay et al. concluded that approximately half (56%) of the observed rate of decline from 1979 to 2005 was externally forced…Based on the CMIP5 multi-model ensemble mean, approximately 60% of the observed rate of decline from 1979-2011 is externally forced…”
Well, you can switch to sea ice extent as a metric, but you asserted multi-decadal oscillatons for ice mass and I’m not seeing much data upthread to support that assertion.
Instead, from the NSIDC upthread, they say:
Glaciologists have found, in study after study, that both of the planet’s remaining ice sheets are losing overall mass at an accelerating rate.
I’m inclined to go with their view, at least right now.
The mass of the ice sheets (which would be Greenland and Antarctica) is not the same as Arctic sea ice extent.
Both ice sheets are losing mass, although I’m not sure the loss rate is accelerating. Look at these two graphs from JPL; the decline looks pretty linear.
At the same time, Arctic SIE has not been decreasing over the last 17 years according to the National Snow & Ice Data Center. Do you have any thoughts on why?
