Northern Greenland warmer 1000 years ago, warmer in the 1920s too

Thanks to the Hockeyschtick for pointing us at a new study of Greenland ice cores[1]. For the first time, 12 ice cores drilled in the northern section of Greenland have been “stacked” and published. Curiously, these 12 ice cores were drilled from 1993 to 1995, so this is not new data– but it’s the first time that all 12 oxygen isotope records, which are a proxy for temperature, have been published together. The area represents about 10% of Greenland, and seems to behave differently to the southern part. The warm event in 1420 is described as a local effect. The researchers acknowledge that solar activity is important and solar activity correlates with temperatures. It must be growing more and more obvious to climate researchers that their models have to include the long term solar cycles.

The take-home messages for me are: 1/ Natural variability is big and unpredictable. 2/ When we get this kind of detail from all the continents and regions of the ocean we’ll definitely be in a position to start getting the big Global Climate Models to work. 3/ Until we figure out how the Sun causes climate change, the current models are useless.

The purple line here shows summer Arctic sea ice extent, which I thought was perfect and stable before we developed coal fired electricity plants.

They don’t find a good correlation with volcanoes or the NAO (North Atlantic Oscillation).

“We find a pronounced warm period from 850 to 1100AD, which has its maximum between 900 and 1000 AD. This is about 100 years earlier than the described MCA in Mann et al. (2009)”

The researchers don’t mention it, but the peak around 950 AD does match the timing in Ljundvist and Christiansen studies for the whole of the Northern Hemisphere.[2][3]

Here they admit the sun has got something to do with the climate — especially the long term shifts.

“In general, higher solar activity causes higher temperatures (as during the MCA) whereas cold periods (e.g. LIA) are dominated by lower solar activity (Ammann et al., 2007). Based on some of the NGT records (B16, B18, B21 and B29), Fischer et al. (1998c) explained most of the long-term variation in northern Greenland by changes in solar activity.”

Local weather owes a lot to the “ice dividing range”:

“…we argue that the main ice divide has a large influence on the spatial δ 18 O pattern representing temperatures. The main ice divide separates the Greenland ice sheet into eastern and western regions (Fig. 1). Cyclonic activity is most important for the precipitation over Greenland.Cyclones forming over Hudson Bay or Baffin Bay and winds from the west or south-west transport air masses to Greenland (Chen et al., 1997).”

The action in any single one ice core is mostly not about what the climate is doing and more to local forces.

“The results of single site ice-core studies are likely weakened by the finding that only 22 % of the local δ 18 O signal is related to climate. 12 % of the variability is attributed to ice sheet topography. The remaining 66 % are therefore due to other processes”

Abstract.

We present for the first time all 12 δ18O records obtained from ice cores drilled in the framework of the North Greenland Traverse (NGT) between 1993 and 1995 in northern Greenland between 74 to 80° N, 36 to 49° W and 2000 to 3200 m a.s.l. The cores cover an area of 680 km × 317 km, ~200 000 km2 or 10 % of the area of Greenland. Depending on core length (100–175 m) and accumulation rate (90–200 kg m−2 a−1) the records reflect an isotope-temperature history over the last 500–1100 years.

The δ18O signal in northern Greenland is influenced by temperature, accumulation and the topography of the North Greenland ice sheet between 72 and 80° N. About 12 % of the variability can be attributed to the position of the single drill sites in relation to the ice sheet topography.

Lowest δ18O mean values occur north of summit and east of the main divide. In general, ice cores drilled on the main ice divide show different results than those drilled east of the main ice divide that might be influenced by secondary regional moisture sources.

A stack of all 12 NGT records and the NGRIP record is presented with improved signal-to-noise ratio. This stack represents the mean δ18O signal for northern Greenland that is interpreted as proxy for temperature. Our northern Greenland δ18O stack indicates isotopically enriched periods compared to their average during medieval times, about 1420 ± 20 AD and from 1870 AD onwards. The period between 1420 AD and 1850 AD was isotopically depleted compared to the average for the entire millennium and represents the Little Ice Age. The 20th century has isotopic values higher than the 1000 years mean and is comparable to the medieval period but lower than about 1420 AD.

Sea ice has a local feedback effect

Around 1420 AD, an anti-correlation between sea-ice extent in the Arctic Ocean (Kinnard et al., 2011) and the δ18O values is observed (Fig. 10). The sea ice in the Arctic Ocean shows a recession in this time of warm temperatures in northern Greenland.

A shrunken sea ice extent would cause higher temperatures on a regional scale and would increase the amount of water vapour from local sources. Therefore, compared to distant sources, more isotopically-enriched moisture (Sime et al., 2013) may contribute to precipitation in northern Greenland, in particular east of main ice divide.However, we do not see any direct relationship between sea-ice extent and our NG-stack during the rest of time. The used sea ice record is an Arctic-wide one, which means that the climatic events of regional extent do not have to be always reflected in the sea ice extent record…

Conclusions

With the full set of the NGT records, it was now for the first time possible to describe regional differences in the δ 18 O values in northern Greenland over the last 1000 years. Because of the ice sheet topography we see a clear east-to-west difference in northern Greenland δ 18 O distribution. The east-to-west gradient is larger than the north-to- south gradient. We find a more pronounced persistence of warm or cold events east of the main ice divide and assume more stable climate conditions there. The eastern part is more influenced by local effects like changes in the Arctic Ocean, which has tobe supported by the results of climate models. For the first, time a local warm event at 1420±20 AD was pointed out. We assume an atmosphere-sea ice feedback as one possible reason for this event. The solar activity and internal Arctic climate dynamics are likely the main factors influencing the temperature in northern Greenland.

REFERENCES

[1^] S. Weißbach, A. Wegner, T. Opel, H. Oerter, B. M. Vinther, and S. Kipfstuhl (2015) Spatial and temporal oxygen isotope variability in northern Greenland – implications for a new climate record over the past millennium , Clim. Past Discuss., 11, 2341-2388, 2015 doi:10.5194/cpd-11-2341-2015 The full text of the Weißbach paper is available through this cached copy.

[2^] Christiansen, B. and Ljungqvist F. C. (2012). The extra-tropical Northern Hemisphere temperature in the last two millennia: reconstructions of low-frequency variability. Climate of the Past, 8(2):765–786, 2012. [abstract] [PDF] [NASA copy] [Discussion on CA noted a lack of complete archives and code]

[3^] Ljungqvist, F. C., Krusic, P. J., Brattström, G., and Sundqvist, H. S (2012).: Northern Hemisphere temperature patterns in the last 12 centuries, Clim. Past, 8, 227-249, doi:10.5194/cp-8-227-2012, 2012. [abstract] [PDF] or try this [PDF] [CO2science discussion]

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