New paper finds models unable to reproduce natural atmospheric oscillations which control climate

A paper under open review for Climate of the Past reconstructs the climate over the past 6,000 years and finds climate models were not able to reproduce the changes in European climate during during the mid-Holocene Climate Optimum, which was warmer than present-day climate. In particular, the authors find the models are unable to reproduce the atmospheric circulations of the Arctic Oscillation [AO] and the North Atlantic Oscillation [NAO] of key importance to European & global climate, and in fact, simulated changes opposite to those found in the climate proxy reconstruction. 

The authors find "The poor representation of [natural] changes in Mid-Holocene atmospheric circulation in models is consistent with similar model deficiencies found [during the present climate], and may be important in understanding why Europe has recently been warming faster than predicted"


The authors determine the primary failing of climate model simulations is an over-reliance and exaggeration of radiative forcing of climate, instead of an emphasis on natural atmospheric and oceanic oscillations and circulatory patterns. The primary obsession of the IPCC is also an over-simplification, exaggeration, and over-reliance that climate is controlled by radiative forcing forcing alone.



Note: the primary influence of the solar variation appears to be via influence of natural atmospheric and oceanic oscillations and circulatory patterns, rather than direct radiative forcing.

Excerpts:

Many of the recent and historical periods of climatic warming in Europe have been explained by changes in atmospheric circulation. For instance, much of the warming that occurred in the late 20th Century in Europe has been attributed to the increased number of winters with a high index AO/NAO (Hurrell, 1995; Visbeck et al., 2001). High index AO/NAO conditions are also thought to have occurred during the Medieval 15 Climate Anomaly, providing a dynamic explanation for the winter warmth experienced  over Europe at this time (Trouet et al., 2009). Similarly in summer, the increased occurrence of heat waves in recent years has been shown to be the result of anomalous atmospheric circulation associated with blocking anticyclones (Kysely and Huth, 2006). This pattern has also been shown to underlie summer warming on longer timescales 20 in the late Holocene (Della-Marta et al., 2007; Trouet et al., 2012; Yiou et al., 2012). 

Changes in atmospheric circulation have a significant influence on European climate (Sepp and Jaagus, 2002; van Ulden and van Oldenborgh, 2006; Hoy et al., 2013), but many climate models have difficulty reproducing this aspect of modern climate (van Ulden and van Oldenborgh, 2006; Woollings, 2010; Kjellstrom et al., 2011; Brands et 25 al., 2013). The warming in Europe during the mid-Holocene simulated in climate models differs fundamentally from that shown in the data, and indicates a high sensitivity in models to the effects of the amplified seasonal insolation cycle experienced at this time, showing greater warming (cooling) in summer (winter) in response to increased (decreased) summer (winter) insolation. Our reconstructed climate in contrast shows a greater warming in winter than in summer at the European scale, and a spatial pattern of anomalies that is more consistent with changes in atmospheric circulation rather than simple direct radiative forcing by insolation. This suggests a greater role for atmospheric dynamics in explaining interglacial warming, and a challenge to conventional ideas about the simple role of Northern Hemisphere high latitude summer insolation in driving interglacial climates. It could also lend support to alternative orbital forcing’s such as the winter latitudinal insolation gradient that has an identical orbital signature to summer insolation, and which could influence the atmospheric circulation through 10 its control of the latitudinal temperature gradient (Davis and Brewer, 2009).

...

Our data-model comparison highlights significant differences between the reconstruction and the model simulation. We explain these differences in terms of atmospheric circulation, which appears strongly imprinted on the reconstructed climate, but subsumed in the model in favour of a simple direct radiative response to the change in the amplitude of the seasonal insolation cycle. We suggest that the MH climate of Europe was characterised by a strong zonal circulation in winter consistent with a positive or high index AO/NAO teleconnection. This brought milder wetter conditions into Northern Europe and cooler drier conditions to many parts of Southern Europe. In summer, we suggest that the zonal circulation was weak, and that anti-cyclonic blocking occurred close to Scandinavia, comparable with a positive or high index SCAND teleconnection. This caused a more meridional circulation, which brought clear skies and dry and warm conditions to Northern Europe, but relatively cooler and somewhat wetter conditions to many parts of Southern Europe. Both of these seasonal changes 5 in atmospheric circulation have been suggested by previous authors, and particularly in the case of the winter AO/NAO, are supported by a large number of studies based on many different proxies.

The poor representation of changes in Mid-Holocene atmospheric circulation in models is consistent with similar model deficiencies found on contemporary timescales, and may be important in understanding why Europe has recently been warming faster than predicted (van Oldenborgh et al., 2009). It also suggests that the atmospheric circulation may be more important in driving interglacial warming than previously considered based on model experiments that appear too sensitive to direct insolation forcing. Future work will extend this MH reconstruction to the complete Holocene, and investigate this problem by comparing this climate record with transient Holocene model simulations.

Clim. Past Discuss., 9, 5569-5592, 2013
www.clim-past-discuss.net/9/5569/2013/
doi:10.5194/cpd-9-5569-2013

The influence of atmospheric circulation on the mid-Holocene climate of Europe: a data-model comparison

A. Mauri¹, B. A. S. Davis^1,*, P. M. Collins¹, and J. O. Kaplan<sup>1,*

1</sup>ARVE Group, Institute of Environmental Engineering, Ecole Polytechnique Fédérale de Lausanne, Switzerland
^*now at: ARVE Group, Institute of Environmental Science, University of Geneva, Switzerland

Abstract. The atmospheric circulation is a key area of uncertainty in climate model simulations of future climate change, especially in mid-latitude regions such as Europe where atmospheric dynamics have a significant role in climate variability. It has been proposed that the mid-Holocene was characterized in Europe by a stronger westerly circulation in winter comparable with a more positive AO/NAO, and a weaker westerly circulation in summer caused by anti-cyclonic blocking near Scandinavia. Model simulations indicate at best only a weakly positive AO/NAO, whilst changes in summer atmospheric circulation have not been widely investigated. Here we use a new pollen-based reconstruction of European mid-Holocene climate to investigate the role of atmospheric circulation in explaining the spatial pattern of seasonal temperature and precipitation anomalies. We find that the footprint of the anomalies is entirely consistent with those from modern analogue atmospheric circulation patterns associated with a strong westerly circulation in winter (positive AO/NAO) and a weak westerly circulation in summer (positive SCAND). We find little agreement between the reconstructed anomalies and those from a climate model simulation, which as with most model simulations shows a much greater sensitivity to local radiative forcing from top-of-the-atmosphere changes in solar insolation. Our findings are consistent with data-model comparisons on contemporary timescales that indicate that models underestimate the role of atmospheric circulation in climate change, whilst also highlighting the importance of atmospheric dynamics in explaining interglacial warming.

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Settled science: New paper finds atmospheric mechanism that removes pollutants, accelerates with warming

The large atmosphere simulation chamber SAPHIR provides a platform for reproducible studies of well-defined atmospheric-chemical mechanisms. 

How Detergent of the Atmosphere Is Regenerated

Oct. 6, 2013 — It sounds unlikely: a washing machine recycles used detergent in order to use it again for the next load of dirty washing. But this is just what happens during the degradation of pollutants in the atmosphere. Jülich scientists have now been able to demonstrate this for the first time for isoprene, the most important natural hydrocarbon. Hydroxyl (OH) radicals -- known as the detergent of the atmosphere -- decompose isoprene in the air. This leads to the creation of new OH radicals, which are then able to purify the air of other pollutants and trace gases. The scientific community had previously only been able to speculate about this mechanism. The new findings have now been published in the scientific journal Nature Geoscience.

The atmosphere has an astonishing ability to cleanse itself. Chemical processes ensure that trace gases and pollutants are removed from the atmosphere -- such as isoprene, which is largely produced by forests. Without these processes global warming would be even more severe and , air quality much poorer. Just a few years ago, scientists thought that the degradation of isoprene considerably reduced the concentration of OH radicals. During studies in China, troposphere researchers from Jülich's Institute of Energy and Climate Research simultaneously determined high concentrations of both OH radicals and trace gases such as isoprene. Other research groups made similar observations in the air above North American forests and tropical rainforests. The obvious conclusion was that during isoprene degradation something happens to regenerate the OH radicals. "In the past few years, there has been an intensive discussion in the scientific community about what this mechanism could be. But without actual proof this remained pure speculation. Now we have succeeded in demonstrating this process," says the Jülich troposphere researcher, Dr. Hendrik Fuchs.

The scientists recreated the natural conditions prevailing in the atmosphere above China and the tropical rainforests in the Jülich simulation chamber, SAPHIR. This chamber enables researchers to simulate the degradation of even slight quantities of trace gases. It is equipped with exactly the same measuring instruments as are used in field experiments. "It is only this particular combination that makes it possible to study the processes precisely. SAPHIR means that we enjoy unique conditions here at Jülich," says head of institute Prof. Andreas Wahner. Jülich scientists were indeed able to confirm the basic principles of this mechanism and to quantify its impact on OH regeneration. The process takes place much faster than thought before, but not so effectively as some researchers had assumed.

Since the degradation process is now understood for isoprene, scientists can begin to quantitatively investigate feedback effects. Relations between self-cleansing processes in the atmosphere and the climate are particularly interesting for the Jülich researchers. More OH radicals in the air mean that more greenhouse gases such as methane can be degraded. Furthermore, in contrast to all other known mechanisms for the degradation of isoprene, less climate-damaging ozone is produced in the atmosphere than previously assumed. Moreover, the effectiveness of the process increases with air temperature. "We may possibly have identified an important interaction between air quality and climate change leading to the accelerated degradation of trace gases in an atmosphere that is heating up," adds the deputy head of institute Dr. Andreas Hofzumahaus.

Journal Reference: DOI:10.1038/ngeo1964
Experimental evidence for efficient hydroxyl radical regeneration in isoprene oxidation

• H. Fuchs,


• A. Hofzumahaus,


• F. Rohrer,


• B. Bohn,


• T. Brauers,


• H-P. Dorn,


• R. Häseler,


• F. Holland,


• M. Kaminski,


• X. Li,


• K. Lu,


• S. Nehr,


• R. Tillmann,


• R. Wegener


• & A. Wahner

• Affiliations


• Contributions


• Corresponding author

Nature Geoscience

 

(2013)

 

doi:10.1038/ngeo1964

Received

 

01 December 2012 

Accepted

 

03 September 2013 

Published online

 

06 October 2013

Article tools

Most pollutants in the Earth’s atmosphere are removed by oxidation with highly reactive hydroxyl radicals. Field measurements have revealed much higher concentrations of hydroxyl radicals than expected in regions with high loads of the biogenic volatile organic compound isoprene^{1, 2, 3, 4, 5,6, 7, 8}. Different isoprene degradation mechanisms have been proposed to explain the high levels of hydroxyl radicals observed^{5, 9, 10, 11}. Whether one or more of these mechanisms actually operates in the natural environment, and the potential impact on climate and air quality, has remained uncertain^12, 13, 14. Here, we present a complete set of measurements of hydroxyl and peroxy radicals collected during isoprene-oxidation experiments carried out in an atmospheric simulation chamber, under controlled atmospheric conditions. We detected significantly higher concentrations of hydroxyl radicals than expected based on model calculations, providing direct evidence for a strong hydroxyl radical enhancement due to the additional recycling of radicals in the presence of isoprene. Specifically, our findings are consistent with the unimolecular reactions of isoprene-derived peroxy radicals postulated by quantum chemical calculations^9, 10, 11. Our experiments suggest that more than half of the hydroxyl radicals consumed in isoprene-rich regions, such as forests, are recycled by these unimolecular reactions with isoprene. Although such recycling is not sufficient to explain the high concentrations of hydroxyl radicals observed in the field, we conclude that it contributes significantly to the oxidizing capacity of the atmosphere in isoprene-rich regions.

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New paper finds multiple amplification mechanisms by which the Sun controls climate

A new paper published in Environmental Research Letters finds multiple solar amplification mechanisms by which small changes in the solar wind and interplanetary magnetic field [IMF] have significant global effects upon atmospheric pressures, the jet stream, weather & climate patterns such as the North Atlantic Oscillation [NAO], storm tracks, Eurasian winter temperatures, and the breakup of Arctic sea ice. 



According to the authors, "Previously, proposals to link solar wind variations to significant weather or climate variability have been dismissed on the grounds that the magnitude of the energy change in the atmosphere associated with the solar wind variability is far too small to impact the Earth’s system. However, this argument neglects the importance of nonlinear tmospheric dynamics"... "Consequently, we have shown that a relatively localized and small-amplitude solar influence on the upper polar atmosphere could have an important effect, via the nonlinear evolution of atmospheric dynamics on critical processes such as European climate and the breakup of Arctic sea ice." 
"In particular, [the solar interplanetary magnetic field changes] affects the structure of the Rossby wavefield, which is key in determining the trajectory of storm tracks [24]. The configuration of the North Atlantic jet stream is particularly susceptible to changes in forcing [25]. In turn, so are the location and the timing of blocking events in this region, in which vortices are shed from the jet stream leading to prolonged periods of low or of high pressure [26]. It has also been proposed that the low-frequency variability of the North Atlantic Oscillation (NAO) arises as a result of variations in the occurrence of upper-level Rossby wavebreaking events over the North Atlantic [27]. The NAO itself is key to climate variability over the Atlantic–European sector stretching from the east coast of the United States to Siberia, and the Arctic to the subtropical Atlantic [28, 25]."



"Our results may therefore provide part of the explanation for previously observed correlations between Eurasian winter temperatures and solar variability."



Excerpts:



Introduction:



Meteorological effects resulting from fluctuations in the solar wind are presently poorly represented in weather and climate models. Indeed, the role of the Sun is one of the largest unknowns in the climate system [1]. The existence of a meteorological response in the polar regions to fluctuations in the dawn–dusk component of the interplanetary magnetic field (IMF), By, is well established [2–5] and is known as the ‘Mansurov effect’. More controversially, there is evidence to suggest that this Sun–weather coupling occurs via the global atmospheric electric circuit [4, 5]. Consequently it has been assumed [6] that the effect maximizes at high latitudes and is negligible at low and mid-latitudes because the perturbation by the IMF is concentrated in the polar regions [7, 8]. However, the spatial variation of the IMF[interplanetary magnetic field]-weather coupling has not been investigated over the whole globe.



In the most detailed study to date [5], variations in IMF By of 8 nT were associated with changes in high-latitude station surface pressure of 1–2 hPa. These correlations were statistically significant for Antarctica between 1995 and 2005, and in the Arctic between 1999 and 2002. The time lag between changes in IMF By and changes in the surface pressure was estimated to be approximately 0 -2 days. Here we extend the analysis, for zero time lag, using 12 UT NCEP/NCAR reanalysis surface pressure [9] data on a global grid ( ; ) where is latitude and is longitude (section 2). A similar spatial analysis of the ionospheric potential for different states of IMF By (section 3) is used to investigate the theory that the response of surface pressure to fluctuations in IMF By occurs via the global atmospheric electric circuit. Our results indicate that a mechanism that is known to produce atmospheric responses to the IMF in the polar regions is also able to modulate weather patterns at mid-latitudes.



Discussion:

...



Previously, proposals to link solar wind variations to significant weather or climate variability have been dismissed on the grounds that the magnitude of the energy change in the atmosphere associated with the solar wind variability is far too small to impact the Earth’s system. However, this argument neglects the importance of nonlinear atmospheric dynamics [20]. The amplitudes of the IMF-related changes in atmospheric pressure gradient are comparable with the initial uncertainties in the corresponding zonal wind used in ensemble numerical weather prediction (NWP) [21] of 1 m s􀀀1. Such uncertainties are known to be important to subsequent atmospheric evolution and forecasting [22]. Consequently, we have shown that a relatively localized and small-amplitude solar influence on the upper polar atmosphere could have an important effect, via the nonlinear evolution of atmospheric dynamics on critical processes such as European climate and the breakup of Arctic sea ice [23]. 



In particular, it affects the structure of the Rossby wavefield, which is key in determining the trajectory of storm tracks [24]. The configuration of the North Atlantic jet stream is particularly susceptible to changes in forcing [25]. In turn, so are the location and the timing of blocking events in this region, in which vortices are shed from the jet stream leading to prolonged periods of low or of high pressure [26]. It has also been proposed that the low-frequency variability of the North Atlantic Oscillation (NAO) arises as a result of variations in the occurrence of upper-level Rossby wavebreaking events over the North Atlantic [27]. The NAO itself is key to climate variability over the Atlantic–European sector stretching from the east coast of the United States to Siberia, and the Arctic to the subtropical Atlantic [28, 25].



Our results may therefore provide part of the explanation for previously observed correlations between Eurasian winter temperatures and solar variability [29, 30], and for the ‘Wilcox effect’ where reductions in the areas of high vorticity in winter storms are seen at times of solar wind heliospheric current sheet crossings [31] (which are characterized by sharp changes between steady, opposite IMF By states).

Full article available here

Environmental Research Letters Volume 8 Number 4

M M Lam et al 2013 Environ. Res. Lett. 8 045001 doi:10.1088/1748-9326/8/4/045001

The interplanetary magnetic field influences mid-latitude surface atmospheric pressure

OPEN ACCESS FOCUS ON HIGH ENERGY PARTICLES AND ATMOSPHERIC PROCESSES

M M Lam, G Chisham and M P Freeman

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The existence of a meteorological response in the polar regions to fluctuations in the interplanetary magnetic field (IMF) component By is well established. More controversially, there is evidence to suggest that this Sun–weather coupling occurs via the global atmospheric electric circuit. Consequently, it has been assumed that the effect is maximized at high latitudes and is negligible at low and mid-latitudes, because the perturbation by the IMF is concentrated in the polar regions. We demonstrate a previously unrecognized influence of the IMF By on mid-latitude surface pressure. The difference between the mean surface pressures during times of high positive and high negative IMF By possesses a statistically significant mid-latitude wave structure similar to atmospheric Rossby waves. Our results show that a mechanism that is known to produce atmospheric responses to the IMF [interplanetary magnetic field] in the polar regions is also able to modulate pre-existing weather patterns at mid-latitudes. We suggest the mechanism for this from conventional meteorology. The amplitude of the effect is comparable to typical initial analysis uncertainties in ensemble numerical weather prediction. Thus, a relatively localized small-amplitude solar influence on the upper atmosphere could have an important effect, via the nonlinear evolution of atmospheric dynamics, on critical atmospheric processes.

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IPCC more confident about greater uncertainty

According to an article published today in Science, "Last week's fifth assessment from the Intergovernmental Panel on Climate Change (IPCC) might appear to suggest that, in spite of decades of intensive study, scientists haven't made one whit of progress on the biggest question in climate: By how much will a doubling of atmospheric carbon dioxide (CO2) levels warm the world? But in fact, climate scientists have greatly tightened constraints on their traditional estimate of how sensitive climate may be to added greenhouse gases."

In what universe does widening the range of CO2 climate sensitivity from 2-4.5C in the last IPCC report to 1.5-4.5C in the new report constitute "greatly tightened constraints"?

In addition, the last IPCC report concluded the "best estimate" of climate sensitivity was 3C, but the new report drops this altogether, stating in a footnote that "No best estimate for equilibrium climate sensitivity can now be given because of a lack of agreement on values across assessed lines of evidence and studies." In the upside-down, cargo-cult world of climate science, greater uncertainty means more confidence.

Science 4 October 2013:  Vol. 342 no. 6154 pp. 23-24   DOI: 10.1126/science.342.6154.23-a

• News & Analysis, Climate Science

The IPCC Gains Confidence in Key Forecast

Richard A. Kerr

Summary

Last week's fifth assessment from the Intergovernmental Panel on Climate Change (IPCC) might appear to suggest that, in spite of decades of intensive study, scientists haven't made one whit of progress on the biggest question in climate: By how much will a doubling of atmospheric carbon dioxide (CO₂) levels warm the world? But in fact, climate scientists have greatly tightened constraints on their traditional estimate of how sensitive climate may be to added greenhouse gases. And they are advancing a new way of gauging how warm it may get by century's end that is easier to estimate and of more use to policymakers.

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New paper finds another amplification mechanism by which the Sun controls climate

A paper published today in Quaternary Science Reviews reconstructs climate of the central Alps over the past 10,000 years and finds precipitation and floods were driven by changes in solar activity. The authors propose variations in solar activity and insolation cause widening and shrinking of the Hadley cell, and influence on the North Atlantic Oscillation [NAO] and Intertropical Convergence Zone [ITCZ]. The paper adds to many other peer-reviewed publications finding solar amplification mechanisms by which small changes in solar activity have large effects on climate.



The authors also find floods and heavy precipitation were more common during cold periods such as the Little Ice Age than during warm periods such as the Medieval Warm Period, the opposite of claims that warming increases precipitation and floods from increased atmospheric water vapor.


According to the authors, "We found that flood frequency was higher during cool periods, coinciding with lows in solar activity. In addition, flood occurrence shows periodicities that are also observed in reconstructions of solar activity from 14C and 10Be records (2500–3000, 900–1200, as well as of about 710, 500, 350, 208 (Suess cycle), 150, 104 and 87 (Gleissberg cycle) years). As atmospheric mechanism, we propose an expansion/shrinking of the Hadley cell with increasing/decreasing air temperature, causing dry/wet conditions in Central Europe during phases of high/low solar activity. Furthermore, differences between the flood patterns from the Northern Alps and the Southern Alps indicate changes in North Atlantic circulation."

Fig. 6. Stacked flood records for the N- and S-Alps (100-year low-pass filtered) spanning (a) the past 10 kyr and (b) the past 2 kyr. Both representations show strong decadal- to millennial-scale fluctuations in flood activity. In a), gray areas and gray arrows mark periods with increased flood activity. In b), important historic and climatic periods characterized by rather high/low flood occurrence are marked with dark/light areas. LIA: Little Ice Age; MCA: Medieval Climate Anomaly; MP: Migration Period; RE: Roman Empire.

Fig. 8. Comparison of the Alpine flood reconstruction to records reflecting solar forcing, as well as to other climate proxy records and reconstructions: a) 30°N summer insolation (Berger and Loutre, 1991); Holocene cold events reported by (b) Wanner et al. (2011) (short gray bars) and (c) Bond et al. (1997) (with numbers 0–6); d) variations in TSI (Steinhilber et al., 2009) (50-year running mean with 100-year smooth); flood activity in the (e) N-Alps and (f) S-Alps (100-year low-pass filtered), on the right: arrow indicates state of the NAO based on S-Alpine flood frequency; g) global glacier advances (Denton and Karlén, 1973); h) NAO reconstruction from Greenland (Olsen et al., 2012); i) precipitation record from the Cariaco Basin (Haug et al., 2001); j) NAO reconstructions covering the past 1000 years (Trouet et al., 2009); k) ssNa concentrations from the GISP2 ice core (56 and 57) (100-year low-pass filtered); l) storminess (0–1) record from the NE United States (Noren et al., 2002). Gray shaded areas and gray arrows mark periods with enhanced flood activity in the Alpine realm. Blue arrows mark periods in the N-Alps that show an opposite flood activity than the S-Alps. Elevated flood activity in the S-Alps is an indicator for a more southerly positioned Atlantic circulation system and a tendency towards lower NAO indices.

Holocene flood frequency across the Central Alps – solar forcing and evidence for variations in North Atlantic atmospheric circulation

• Stefanie B. Wirth^{a, , 1, 2,} , 


• Lukas Glur^b, 2, 


• Adrian Gilli^a, 


• Flavio S. Anselmetti^b, c

• ^a Geological Institute, ETH Zurich, Zurich, Switzerland


• ^b Eawag, Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, Switzerland


• ^c Institute of Geological Sciences and Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland

Highlights

•

Lake sediments are a valuable terrestrial archive of past flood events.

•

High flood frequency in the Alps is driven by low solar activity.

•

Widening/shrinking of the Hadley cell brings dry/wet conditions to the Alps.

•

South-Alpine flood frequency indicates changes in a paleo-NAO pattern.

•

Frequent S-Alpine floods suggest a southerly position of the N-Atlantic circulation.

---

Abstract

The frequency of large-scale heavy precipitation events in the European Alps is expected to undergo substantial changes with current climate change. Hence, knowledge about the past natural variability of floods caused by heavy precipitation constitutes important input for climate projections. We present a comprehensive Holocene (10,000 years) reconstruction of the flood frequency in the Central European Alps combining 15 lacustrine sediment records. These records provide an extensive catalog of flood deposits, which were generated by flood-induced underflows delivering terrestrial material to the lake floors. The multi-archive approach allows suppressing local weather patterns, such as thunderstorms, from the obtained climate signal. We reconstructed mainly late spring to fall events since ice cover and precipitation in form of snow in winter at high-altitude study sites do inhibit the generation of flood layers. We found that flood frequency was higher during cool periods, coinciding with lows in solar activity. In addition, flood occurrence shows periodicities that are also observed in reconstructions of solar activity from ¹⁴C and ¹⁰Be records (2500–3000, 900–1200, as well as of about 710, 500, 350, 208 (Suess cycle), 150, 104 and 87 (Gleissberg cycle) years). As atmospheric mechanism, we propose an expansion/shrinking of the Hadley cell with increasing/decreasing air temperature, causing dry/wet conditions in Central Europe during phases of high/low solar activity. Furthermore, differences between the flood patterns from the Northern Alps and the Southern Alps indicate changes in North Atlantic circulation. Enhanced flood occurrence in the South compared to the North suggests a pronounced southward position of the Westerlies and/or blocking over the northern North Atlantic, hence resembling a negative NAO state (most distinct from 4.2 to 2.4 kyr BP and during the Little Ice Age). South-Alpine flood activity therefore provides a qualitative record of variations in a paleo-NAO pattern during the Holocene. Additionally, increased South Alpine flood activity contrasts to low precipitation in tropical Central America (Cariaco Basin) on the Holocene and centennial time scale. This observation is consistent with a Holocene southward migration of the Atlantic circulation system, and hence of the ITCZ [Intertropical Convergence Zone], driven by decreasing summer insolation in the Northern hemisphere, as well as with shorter-term fluctuations probably driven by solar activity.

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Helping the IPCC with decadal trend graphs

The IPCC AR5 has a new "decadal average" graph designed to hide the statistically insignificant global warming over the past 20 years. Since nobody wants to be accused of cherry-picking starting dates and using a decadal average instead of a decadal trend line, let's graph the decadal linear trends for each starting year since 1988. This paints a quite different picture than the IPCC decadal average graph, showing a clear halt in "decadal average" and "decadal trend" global warming starting at the beginning of the 21st century.

The decadal mean temperature graph 

October 1, 2013 Reblogged from The IPCC Report

Perhaps the most ridiculous graph in the IPCC AR5 SPM is this one showing “decadal mean” temperature.





A few points about this graph: 

As far as I know, such a graph has not been used in any peer reviewed publication
The graph was not in the draft version of the SPM subjected to expert review
No such graph has been used in any of the previous IPCC reports.
I’m not aware of any such graph being used in any other field of science – any examples?

So why is the graph so bad? It’s hard to see why it is necessary to point this out. Firstly, it takes a graph with about 160 data points on it, and reduces this to just 16, effectively throwing away most of the data. Secondly, the appearance of the graph depends very much on how you choose to do the 10-year cuts. They seem to have chosen either 0-9 or 1-10 bins (it’s not clear which) so that the last two or three years aren’t included at all. But if we chose 5-4 bins, the picture would probably look quite different (has anybody done this?). The introduction of this graph into AR5, with no such graph in the previous reports, leaves the IPCC open to accusations of trying to “hide the decline” in warming this decade, though of course the levelling off is clear in the graph above, so the graph seems quite pointless.

In the draft version of the SPM reviewed by scientists, this graph was not there, perhaps because the authors were aware that it might be criticised. This illustrates the point about the authors having carte blanche to insert whatever they like into the final version after the review. The decadally averaged graph was there in the main section of the report, in chapter 2, Fig 2.20 (In the final draft version, it is Fig 2.19). In my review comments, I was very critical of this graph (“Fig 2.20 – I am surprised to see this absurd figure still in the SOD. No such figure appears in the cited paper Morice et al, or in any other published paper I am aware of , or in previous IPCC reports. Such a figure would be widely and rightly ridiculed as an attempt disguise the recent slow-down of warming.”)

The IPCC responded to my criticism by putting the graph in the SPM.

I have not seen much comment on this graph. But Reiner Grundmann tweeted “Summary for policymakers dodges issue of ‘pause’ in global warming. New fig.1 makes problem invisible” and “So SPM replaced the ‘dodgy sandwich’ graph with an ‘elevator’ graph of decadal temp rise. Good PR, but is it sustainable?” on the day the SPM was published.

This type of graph seems to have originated in a Met Office press release from 2009, although the IPCC version seems to be based on this one from 2012 from the EEA.

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New paper finds E. Antarctic ice shelf gaining more ice mass than previously believed

A paper published today in the Journal of Geophysical Research - Atmospheres finds the East Antarctica Fimbul ice shelf has accumulated significantly more ice mass over the past 26 years than previously believed. According to the authors, "the 26-year mean [surface ice mass balance] on the Fimbul ice shelf varies between 170 and 620 [kilograms per meter squared per year] giving a regional average value of 310 ±70 kg  [per meter squared per year]. Our measurements indicate higher long-term accumulation over large parts of the ice shelf compared to the [prior] large-scale studies."


Surface mass balance on Fimbul ice shelf, East Antarctica: comparison of field measurements and large-scale studies

Abstract:

Many challenges remain for estimating the Antarctic ice sheet surface mass balance (SMB), which represents a major uncertainty in predictions of future sea-level rise. Validating continental scale studies is hampered by the sparse distribution of in-situ data. Here we present a 26-year mean SMB of the Fimbul ice shelf in East Antarctica between 1983–2009, and recent interannual variability since 2010. We compare these data to results of large-scale SMB studies for similar time periods, obtained from regional atmospheric modeling and remote sensing. Our in-situ data include ground penetrating radar, firn cores and mass balance stakes, and provide information on both temporal and spatial scales. The 26-year mean SMB on the Fimbul ice shelf varies between 170 and 620 kg m^-2 a^-1 giving a regional average value of 310 ±70 kg m^-2 a^-1. Our measurements indicate higher long-term accumulation over large parts of the ice shelf compared to the large-scale studies. We also show that the variability of the mean annual SMB, which can be up to 90 %, can be a dominant factor in short-term estimates. The results emphasize the importance of using a combination of ground based validation data, regional climate models and remote sensing over a relevant time period in order to achieve a reliable SMB for Antarctica.

Related: 

ICESAT Data Shows Mass Gains of the Antarctic Ice Sheet Exceed Losses

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