What caused Warm Periods in the Arctic?

[BethesdaWX]

I'd like to keep AGW out of this, and rather focus on the causation of the MWP, and other Warm Episodes specifically in Greenland and Arctic Regions.

The Greenland/Arctic Region, specifically, was relatively "toasty" during these "warm episodes"....to where viking settlments, burial grounds, animal pastures, etc are being uncovered under todays melting Glaciers. Seeing wheat and barley remains, and even small residences, really confirms this.

But the Question is why? Volcanism and changes from TSI Directly cannot explain it, and neither can GHG changes.

I'd think discussion on this would be interesting.

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[Snow_Miser]

Interesting topic Bethesda. Could it possibly be the changes in GCC due to GCR fluctuations? It is certainly plausable, since we do not have an accurate record on Total GCC going back 10,000 years, and especially, since it has been shown, that changes in GCC have 3X the impact than GHGs do.

[BethesdaWX]

Interesting topic Bethesda. Could it possibly be the changes in GCC due to GCR fluctuations? It is certainly plausable, since we do not have an accurate record on Total GCC going back 10,000 years, and especially, since it has been shown, that changes in GCC have 3X the impact than GHGs do.

Thanks, and yes that is very true regarding Clouds, but I'm trying not to go into AGW (invloving greenhouse gases in any way). I'm wondering more about what would have caused it to remain so low for so long, at least regionally, knowing how Greenland and the Arctic Region were So warm for so Long, in the Means for the Holocene, that I think something must have driven that change in GCC (if it were the cause).

Sometimes I wonder if it may have something to do with the changes in global Ocean Currents, and perhaps those either effect GCC, or the regional climate. Unfortunately, we do not know of any "regional" potential Impact from that over thousands of years.

[skierinvermont]

If it were clouds, these temperature fluctuations would be global and many of them are not (and some of them are). GCRs have been shown over and over and over by multiple methods to have minimal effect on climate.

I doubt we will ever know the exact causes of all of the regional (or global) warm and cool periods so I'm not going to invent some far-fetched theory with no real proof. There is good evidence that the MWP was mostly caused by low volcanic activity and high TSI.

[BethesdaWX]

If it were clouds, these temperature fluctuations would be global and many of them are not (and some of them are). GCRs have been shown over and over and over by multiple methods to have minimal effect on climate.

I doubt we will ever know the exact causes of all of the regional (or global) warm and cool periods so I'm not going to invent some far-fetched theory with no real proof. There is good evidence that the MWP was mostly caused by low volcanic activity and high TSI.

Yes you are 100% Correct, GCR's have been shown to have very minimal effects on climate between solar cycles in the time we have measured (which is unfortunately relatively short to the scale of incoming Neuronal baseline change), but thats all we can conclude........and since we have not measured long enough, it cannot be proven that GCR's had anything to due with the warm periods in the Arctic/Greenland Specifically, especially if the warm arctic was Regional, which is very possibly the case. But the Mechanism is still a possibility.

If GCR's have a longer term (multi-century) impact on Low Clouds, there is no way we can possibly know about it at this time, especially since we cannot even measure clouds accurately to this day. Before we can consider a mechanism, we need to be able to measure it first. So thats really the end of that.

But there are several problems

The types of proxies used also pose an issue. The highest resolution proxies (ice cores), are only found on the poles. So determining past Polar Temperatures is much easier than determining the past global temperature. Another problem.....as of right now, we do not know of any driver that could Warm One region/Hemisphere of the Planet significantly, alone in deviation from the rest of the Globe. Volcanism or Lack There-of, will have global impact of fairly equal significance, and TSI also would warm the globe evenly.

So to determine the driver of the Warm Arctic in the Holocene, either

1) It was a regional event caused by some unknown forcing or change in Ocean circulation that kept the Temperatures at the Poles, Several Centigrade warmer/cooler fluctuations in regards to its relative AVG, while the global temperature outside the poles was not relatively divergent from its avg and remained steady. This seems unlikely, but it is certainly possible.

2) It was a global event, but more concentrated un the Polar regions (Polar temperatures deviate more-so than those of the equator, for example), and smaller scale changes at the equator of 0.5-C to 1C may be harder to pick up. This may seem more plausible on the surface, but it still has its likely errors. Since from what we know, there are no drivers that could change the global temperature to that significant of an extent, and thats where we need to go back to the #1 scenario.

In theory, changes in Cloud Cover could do it, but no mechanism can be established at this time, and we can only theorize/hypothesize. Changes in Ocean Circulations could also theoretically accomplish this, but that would also have a global effect.

So there could likely be something we're missing.

[Clifford]

Keep in mind that the ice cores represent a combination of local and global conditions due to measuring the deposition of ²H and ¹⁸O as water vapor components that may have evaporated in somewhat distant locations. It certainly doesn't represent water subliming or evaporating from the ice covered continent and being redeposited.

When you look at the weather and temperatures, it follows very much a fractal pattern, relating to both endogenous and exogenous causes.

• On an hour-by-hour basis you have clouds that may float past the sun to obscure it, or dump their loads of rain or snow to cool the surface below.
• On a daily basis, you have the rotation of the Earth and daytime warming and nightime cooling.
• On an annual basis you have winter cooling and summer warming dictated by the tilt of the planet's axis.
• El Niño/La Niña currents toss around the temperature and rainfall patterns over a couple of year basis.
• AMO & PDO currents toss around the temperatures on a few decade basis. At this point, I'm not sure we have a good explanation of the causes of the ocean current shifts.
• We seem to have about 1000 year cycles (this topic).
• A 41,000 year glacial/interglacial cycle.
• A 100,000 year glacial/interglacial cycle.
• A 25 million year pattern.
• A 100 million year pattern (in which we remain in a cold phase).
• And, perhaps even a billion year cycle.

It is noted that the reason we don't have extremely long Antarctica records is that it is believed that the Antarctic ice has periodically melted and refrozen many times throughout Earth's history.

At this point, some parts of warming/cooling patterns may be supported by CO₂, Milankovitch Cycles, Asteroid Impacts, etc. But there have to be additional factors too, especially for periods either longer or shorter than would be predicted by the Milankovitch theory.

I think there is quite a bit of evidence that the Little Ice Age and Marauder Minimum correlates with a period of weak solar activity. That would lead me to believe that similar cool periods between the highlighted green segments above (Minoiske Warm Period, Roman Warm Period, and Medieval Warm Period) may also have been attributable to weak solar activity, and likewise the warm periods were caused by increased solar activity.

There are other disturbing feedback mechanisms that have been suggested for cold periods and oscillation between warm and cold. For example, the suggestion that our ocean currents require somewhat of a homogenous salt content. Slow ice melt should allow the low density freshwater to get distributed around the ocean. However, a rupture of a large ice-dam in the North could allow rapid flow of large amounts of freshwater into the Arctic. This then lowers the density of the Arctic water, and prevents the downward flow of the water into the tropical deep ocean areas. And then prevents tropical warm water from being brought northward. The result being rapid chilling of Europe and perhaps much of the Northern Hemisphere.

So, if a freshwater lake the size of Lake Michigan was to form in Greenland, then rapidly dump its water into the Arctic, it could cause rebound cooling of the area, and then more cooling and accumulation of ice in Greenland.

Even sea ice contains a large proportion of fresh water. So, rapid melt of sea ice might also cause rebound effects of cold in the North, which is likely related to the multi-year oscillations of sea ice extent.

I can't imagine that fresh vs salt water could account for 1000 year oscillations though. I'd expect it to be more related to El Nino/La Nina, PDO, and AMO oscillations.

Although, a breakdown of the gulf stream would likely not only cause Northern cooling, but also tropical deep ocean warming, and a breakdown of the tropical clathrates which theoretically could result in multi-year warming.

Nothing with the Milankovitch Cycles is on a 1000 cycle either, with one of the shortest, but perhaps more dominant patterns being apsidal precession that occurs over about 22,000 years for a full cycle, or 11,000 years for a half-cycle.

One of the papers that you posted earlier indicated that CO₂ might have a synergistic cooling effect by radiating heat into the upper atmosphere quicker than other gases. It is actually a very troubling thought, but I am doubtful as we should be seeing such an effect now, but aren't. It could, however, be balancing the warming and potential cooling effects of CO₂.

I suppose a marginal forest could also run in 1000 year cycles of rapid growth and decline, altering atmospheric gases. But again little evidence for such widespread impacts.

Anyway, given the evidence of the correlation of the Little Ice Age and Marauder Minimum with weak solar activity, I'm back to the conclusion that the warmer periods are caused by stronger solar activity.

[ArtRosen]

This is a great discussion and really interesting. I'm having a hard time figuring out the abbreviations though. Is there a link I can go to that will help me with this? Specifically, GOC, TSI, GHG, etc.

[Clifford]

This is a great discussion and really interesting. I'm having a hard time figuring out the abbreviations though. Is there a link I can go to that will help me with this? Specifically, GOC, TSI, GHG, etc.

We do need a sticky glossary, as new abbreviations seem to pop up all the time.... and then someone assumes everyone knows about it. I believe that "GOC" is a typo.

AMO: Atlantic Multidecadal Oscillation. Overall Warm vs cool anomaly of the North Atlantic Ocean, with a 40 - 60 year full cycle oscillation.

CO₂: Carbon Dioxide

CH₄: Methane Gas

El Niño / La Niña / ENSO (El Niño Southern Oscillation) is an ocean current in the Pacific that has Global effects. Cooler equatorial temperatures are a sign of La Niña currents. Warmer equatorial currents are a sign of El Niño currents. La Niña years are often cooler globally, and El Niño years are often warmer globally.

GHG: Green House Gas (Carbon Dioxide, Methane, Various refrigerants, etc).

GCC: Global Cloud Cover

PDO: Pacific Decadal Oscillation. A multi-year oscillation somewhat related to ENSO, but dealing with the North Pacific. "Cool" means cold water in the Northeast Pacific near the Northwest coast of the USA/Canada and warm temperatures in the Northwest Pacific near Asia.

TSI: Total Solar Irradiance. It is a measurement of the energy arriving at the upper atmosphere of the Earth from the sun. The sun, along with sunspots goes through about a 10 year cycle of higher TSI and lower TSI. There is some debate on how much it varies over longer periods of centuries, millenia, or hundreds of thousands of years.