Models show natural swings in the Earth’s climate contribute to Arctic sea ice loss
Arctic sea ice loss in the last 37 years is not due to humans alone.
By Anne L. Stark, LLNL
New research by a Lawrence Livermore National Laboratory (LLNL) scientist and collaborators show that Arctic sea ice loss is enhanced by natural climate fluctuations such as El Niños and La Niñas. With manmade greenhouse gases on top of the natural climate variability, the decrease in sea ice is even more severe than climate models originally estimated.
Using a series of climate models, the team used a “fingerprint” method to estimate the impact of natural climate variability. Natural swings in the Earth’s climate contribute to about 40 percent to 50 percent of the observed multi-decadal decline in Arctic sea ice.
“Internal variability can enhance or mute changes in climate due to greenhouse gas emissions. In this case, internal variability has tended to enhance Arctic sea ice loss,” said Stephen Po-Chedley, an LLNL climate scientist and a co-author on a paper appearing in the Nov. 5 edition of Nature Geoscience.
As it turns out, observations of sea ice loss were larger than models predicted. Sea ice loss since 1979 has increased due to natural variability; observations show more Arctic sea ice loss than the climate models average.
“It is important to note that individual runs do show large changes in sea ice that are comparable to observed sea ice changes,” Po-Chedley said. “In these simulations, like in the real world, Arctic sea ice loss was enhanced by natural climate variability.
“When natural variability is taken into account, Arctic sea ice loss is quite similar across models and observations.”
According to NASA, the planet has been shedding sea ice at an average annual rate of 13,500 square miles (35,000 square kilometers) since 1979, the equivalent of losing an area of sea ice larger than the state of Maryland every year.
Model simulations (or “runs”) exhibit a range of sea ice trends. Depending on the timing of natural fluctuations, individual model runs can exhibit greater or smaller-than-average loss. Similarly, both natural variability and greenhouse gas changes contribute to the observed sea ice loss.
“This study helps to quantify the degree to which natural and anthropogenic factors contributed to Arctic sea ice loss over the last few decades,” Po-Chedley said.
The team found that enhanced ridging over the Arctic Ocean promotes warming and moistening in the lower troposphere (the lowest layer of Earth’s atmosphere where nearly all weather conditions take place), which in turn, leads to accelerated sea ice loss. Arctic sea ice decline may be important to rainfall in California. Previous research has suggested that Arctic sea ice loss can exacerbate droughts over California.
Other institutions contributing to the work include University of California, Santa Barbara, University of Washington, National Oceanic and Atmospheric Administration (NOAA) Climate Prediction Center, Princeton University and the Geophysical Fluid Dynamics Laboratory.
The paper (paywalled): https://www.nature.com/articles/s41561-018-0256-8
Fingerprints of internal drivers of Arctic sea ice loss in observations and model simulations
Abstract
The relative contribution and physical drivers of internal variability in recent Arctic sea ice loss remain open questions, leaving up for debate whether global climate models used for climate projection lack sufficient sensitivity in the Arctic to climate forcing. Here, through analysis of large ensembles of fully coupled climate model simulations with historical radiative forcing, we present an important internal mechanism arising from low-frequency Arctic atmospheric variability in models that can cause substantial summer sea ice melting in addition to that due to anthropogenic forcing. This simulated internal variability shows a strong similarity to the observed Arctic atmospheric change in the past 37 years. Through a fingerprint pattern matching method, we estimate that this internal variability contributes to about 40–50% of observed multi-decadal decline in Arctic sea ice. Our study also suggests that global climate models may not actually underestimate sea ice sensitivities in the Arctic, but have trouble fully replicating an observed linkage between the Arctic and lower latitudes in recent decades. Further improvements in simulating the observed Arctic–global linkage are thus necessary before the Arctic’s sensitivity to global warming in models can be quantified with confidence.
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The time plots show global sea ice to be basically flat since 1979
https://wattsupwiththat.wordpress.com/reference-pages/sea-ice-page/
Humlum’s sea ice page at http://www.climate4you.com/
shows the same thing
CO2 forcing has almost nothing to do with Arctic Sea Ice Extents.
Arctic Sea Ice Extents follow 30-year PDO, AMO and NAO ocean cycle, which is why there has been no statitistically signicant decreasing trend since the PDO ended its 30-year warm cycle in 2008.
Since 2008, there have been a few one-off events like the 2012 Super Cyclone (strongest and longest in 50 years) and the 2015/16 Super El Niño, but even with these events, Arctic Sea Ice Extents have been relatively stable.
When the PDO, AMO and NAO are all in their respective 30-year cool cycles from early 2020’s , Arctic Sea Ice Extents will begin to gradually recover back to 1980 levels.
There will also be a Grand Solar Minimum event starting from 2021, which will likely add to global cooling and contribute to Arctic Ice Extent recovery.
In about 4 years, CAGW advocates will have a very difficult time explaining why Arctic Ice Extents and Greenland Land Ice Mass are recovering, and why a global cooling trend is developing, despite 30%+ of all CO2 emissions since 1750 being made over just the last 25 years..
We’ll see soon enough.
BTW, CAGW cultists predicted the Arctic would be “ice free” from the summer of 2012… not so much…Funny how they forgot about that prediction already…
I would wager that it is not at all due to human-emitted carbon dioxide.
There is a case for human produced soot having a very minor contribution.
But CO2, there is absolutely no logical scientific mechanism that could cause CO2 to melt Arctic sea ice..
There is something really simple about the model ensemble graphs, the spaghetti chart, that I don’t understand. Maybe someone could help?
Why does anyone think, if they do, that the average of a bunch of failing and succeeding models is of any value?
Why do they not just use the ones that have succeeded and junk the failing ones? Why is the emphasis apparently not on getting and using good models, but on continuing to use the ones proven to have failed?
And why does anyone think that just because a couple of models at the very bottom of the huge range of FAILURES go somewhere near reality, they actually represent reality, rather than just blind luck. !
“Why is the emphasis apparently … on continuing to use the ones proven to have failed?”
Because then some of the Pals would lose their funding. Can’t have that.
Michel, indeed there is one model, INMCM5 in its latest version that performs quite closely to HADCrut4, though still has difficulty replicating periods of cooling. My synopsis of what is in that model and why it is worth studying:
There appear to be 3 features of INMCM4 that differentiate it from the others.
1.INMCM4 has the lowest CO2 forcing response at 4.1K for 4XCO2. That is 37% lower than multi-model mean.
2.INMCM4 has by far the highest climate system inertia: Deep ocean heat capacity in INMCM4 is 317 W yr m^-2 K^-1, 200% of the mean (which excluded INMCM4 because it was such an outlier)
3.INMCM4 exactly matches observed atmospheric H2O content in lower troposphere (215 hPa), and is biased low above that. Most others are biased high.
So the model that most closely reproduces the temperature history has high inertia from ocean heat capacities, low forcing from CO2 and less water for feedback. Why aren’t the other models built like this one?
https://rclutz.wordpress.com/2018/10/22/2018-update-best-climate-model-inmcm5/
Ron,
Thanks for this. I guess it is a real if unacknowleged issue. I had hoped to get the pro argument from someone like Nick Stokes, but maybe there simply isn’t one. It seems like an enormous logical howler, its hard to believe I am the only one to be puzzled if so.
37 Years?
Is that a surprise for anyone?
Starting 1979-that is no surprise for me
The coolest year in a 60 Years cycle.
AMO:
https://en.wikipedia.org/wiki/Atlantic_multidecadal_oscillation#/media/File:Atlantic_Multidecadal_Oscillation.svg
When the abstract states
“….through analysis of large ensembles of fully coupled climate model simulations with historical radiative forcing…”
is it worth reading any more?
Abstract
An internal oscillation has been identified in the degree of acknowledgment by the scientific community of natural climatic cycles. Periods during which climate oscillation is acknowledged alternate with periods during which it is denied, or not mentioned. Here we find that oscillation in the climate itself periodically forces the fluctuation in acknowledgment of those cycles. When climatic oscillation is in a cooling phase, there is a distinct step-up in acknowledgment of and research into the role of natural internal variability in scientific publications and communications. Conversely, when the same climate oscillation turns to a warming phase, silence abruptly descends on the topic of natural climate variability and climate cycles are denied. Since this periodically forced oscillation in the profile and acknowledgment of climate variability is drive by alternating phases of positive feedback in opposite directions, this leads to a simple monotonic oscillation and a relationship of strong nonlinear periodic forcing, between the phase of natural climate variation, and the willingness of climate scientists to acknowledge and focus research effort on those same cycles.
Arctic sea ice loss in the last 37 years is due to AMO alone.
tell it to the Russians and Mersk. Both are aiming to make millions on shipping from-to China and points East.
“40 to 50 percent”: sure, why not? that leaves 50 to 60 percent due to human causes; quite significant.
to me its about who profits, and I don’t fancy Russians and Chinese making billions while we could be (a) paying much less for energy (solar and wind are free, nuke is sunk costs), and (b) missing out on the jobs that green tech provides (without killing coal miners)
“green tech” kills jobs, so we see what your agenda is.