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Climate Hustle

New research from last week 36/2012

Posted on 11 September 2012 by Ari Jokimäki

I spent most of the last week cataloging all the surveys that didn't send me an e-mail, but I did also have a peek on new research papers published last week. Some of them are presented below.


Exceptionally hot summer frequency has increased in Central and Eastern Europe

Exceptionally hot summers in Central and Eastern Europe (1951–2010) - Twardosz & Kossowska-Cezak (2012) [FULL TEXT]

Abstract: "The paper focuses on exceptionally hot summers (EHS) as a manifestation of contemporary climate warming. The study identifies EHS occurrences in Central and Eastern Europe and describes the characteristic features of the region’s thermal conditions. Average air temperatures in June, July and August were considered, as well as the number of days with maximum temperatures exceeding 25, 30 and 35 °C, and with a minimum temperature greater than >20 °C, as recorded at 59 weather stations in 1951–2010. Extremely hot summers are defined as having an average temperature equal to or greater than the long-term average plus 2 SD. A calendar of EHSs was compiled and their spatial extent identified. The region experienced 12 EHSs, which occurred in a given year at 5 % or more stations (1972, 1981, 1988, 1992, 1997, 1998, 1999, 2002, 2003, 2006, 2007 and 2010). The EHS frequency of occurrence was found to be clearly on an increase. Indeed, only one EHS occurred during the first 30 years, but these occurred five times during the last 10 years of the study period. Their geographical extent varied both in terms of location and size. EHSs were observed at 57 out of the total of 59 weather stations in the study (the exceptions were Pecora and Cluj). The average air temperature of EHSs tended to exceed the relevant long-term average by 2–4 °C. The summer of 2010 was among the hottest (temperature anomaly 5.5–6 °C) and spatially largest."

Citation: Robert Twardosz and Urszula Kossowska-Cezak, Theoretical and Applied Climatology, 2012, DOI: 10.1007/s00704-012-0757-0.


Inorganic carbon content of the top layer of soil in China's grasslands has decreased

Widespread decreases in topsoil inorganic carbon stocks across China's grasslands during 1980s-2000s - Yang et al. (2012)

Abstract: "Soil carbon (C) stocks consist of inorganic and organic components, ~ 1.7 times larger than the total of the C stored in vegetation and the atmosphere together. Significant soil C losses could thus offset any C sink in vegetation, creating a positive feedback to climate change. However, compared with the susceptible sensitivity of organic matter decay to climate warming, soil inorganic carbon (SIC) stocks are often assumed to be relatively stable. Here we evaluated SIC changes across China's grasslands over the last two decades using data from a recent regional soil survey during 2001-2005 and historical national soil inventory during the 1980s. Our results showed that SIC stocks in the top 10 cm decreased significantly between the two sampling periods, with a mean rate of 26.8 (95%CI: 15.8-41.7) g C m-2 yr-1. The larger decreases in SIC stocks were observed in those regions with stronger soil acidification and richer soil carbonates. The lost SIC could be released to the atmosphere as carbon dioxide, redistributed to the deeper soil layer, and transferred to the nearby regions. The fraction of soil carbonates entering into the atmosphere may diminish the strength of terrestrial C sequestration and amplify the positive C-climate feedback."

Citation: Yuanhe Yang, Jingyun Fang, Chengjun Ji, Wenhong Ma, Anwar Mohammat, Shifeng Wang, Shaopeng Wang, Arindam Datta, David Robinson, Pete Smith, Global Change Biology, DOI: 10.1111/gcb.12025.


Watching the tropics grow

An observational analysis of Southern Hemisphere tropical expansion - Lucas et al. (2012) [FULL TEXT]

Abstract: "Historical radiosonde data are analyzed using the tropopause height frequency method to investigate the variation of the Southern Hemisphere tropical edge from 1979/80–2010/11, independently of reanalysis-derived data. Averaged across the hemisphere we identify a tropical expansion trend of 0.41 ± 0.37 deg dec−1, significant at the 90% level. A comparison with four reanalyses shows generally consistent results between radiosondes and reanalyses. Estimated rates of tropical expansion in the SH are broadly similar, as is the interannual variability. However, notable differences remain. Some of these differences are related to the methodology used to identify the height of the tropopause in the reanalyses, which produces inconsistent results in the subtropics. Differences between radiosondes and reanalyses are also more manifest in data-poor regions. In these regions, the reanalyses are not fully constrained, allowing the internal model dynamics to drive the variability. The performance of the reanalyses varies temporally compared to the radiosonde data. These differences are particularly apparent from 1979 to 1985 and from 2001 to 2010. In the latter period, we hypothesize that the increased availability and quality of satellite-based data improves the results from the ERA Interim reanalysis, creating an inconsistency with earlier data. This apparent inhomogeneity results in a tropical expansion trend in that product that is inconsistent with the radiosonde-based observations. These results confirm the need for careful evaluation of reanalysis-based data for use in studies of long-term climate variability."

Citation: Lucas, C., H. Nguyen, and B. Timbal (2012), An observational analysis of Southern Hemisphere tropical expansion, J. Geophys. Res., 117, D17112, doi:10.1029/2011JD017033.


Species abundances and distributions have changed in response to post-LIA and late twentieth century climate warming

Faunal (Chironomidae, Cladocera) responses to post-Little Ice Age climate warming in the high Austrian Alps - Nevalainen & Luoto (2012)

Abstract: "Present climate warming strongly affects limnological and ecological properties of lakes and may cause regime shifts that alter structure and function in the water bodies. Such effects are especially pronounced in climatologically extreme areas, e.g. at high altitudes. We examined a sediment core from Lake Oberer Landschitzsee, Austrian Alps, which spans the period from the Little Ice Age (LIA) to present. We investigated whether post-LIA climate warming altered aquatic invertebrate communities and limnological status in this sensitive high Alpine lake. Fossil Cladocera (Crustacea) and Chironomidae (Diptera) and organic matter in the core were analyzed. Chironomids were used to assess the lake’s benthic quality (i.e. oxygen availability). An instrumental Alpine temperature record was used to assess whether changes in the biotic assemblages correspond to post-LIA temperature trends. The planktonic and macro- and microbenthic invertebrate communities exhibit almost complete and simultaneous species turnover after the LIA, from about AD 1850 onward, when Sergentia coracina-type replaced oxyphilous Micropsectra contracta-type as the dominant macrobenthic taxon, and phytophilous Acroperus harpae outcompeted Alona affinis and Alona quadrangularis in the microbenthos. These directional community shifts corresponded with a period of reduced benthic quality, higher sediment organic content, and progressive climate warming, superimposed on Alpine land-use changes, until the early twentieth century. Detected changes suggest increased productivity and lower benthic oxygen availability. Faunal shifts were even more pronounced during the late twentieth century, simultaneous with enhanced warming. A new planktonic Cladocera species, Bosmina longirostris, typically absent from high Alpine lakes, colonized the lake and gradually became dominant toward the core top. Results show that post-LIA climate warming, coupled with increasing benthic and planktonic production, substantially altered the limnological and ecological status of this remote Alpine lake. Observed faunal turnovers provide evidence that temperature-driven ecological thresholds, whether associated directly or indirectly with greater human activity, have been crossed. Species abundances and distributions have changed in response to post-LIA and late twentieth century climate warming."

Citation: Liisa Nevalainen and Tomi P. Luoto, Journal of Paleolimnology, 2012, DOI: 10.1007/s10933-012-9640-3.


How much carbon has accumulated in long-lived products such as buildings and furniture?

Global socioeconomic carbon stocks in long-lived products 1900–2008 - Lauk et al. (2012) [FULL TEXT]

Abstract: "A better understanding of the global carbon cycle as well as of climate change mitigation options such as carbon sequestration requires the quantification of natural and socioeconomic stocks and flows of carbon. A so-far under-researched aspect of the global carbon budget is the accumulation of carbon in long-lived products such as buildings and furniture. We present a comprehensive assessment of global socioeconomic carbon stocks and the corresponding in- and outflows during the period 1900–2008. These data allowed calculation of the annual carbon sink in socioeconomic stocks during this period. The study covers the most important socioeconomic carbon fractions, i.e. wood, bitumen, plastic and cereals. Our assessment was mainly based on production and consumption data for plastic, bitumen and wood products and the respective fractions remaining in stocks in any given year. Global socioeconomic carbon stocks were 2.3 GtC in 1900 and increased to 11.5 GtC in 2008. The share of wood in total C stocks fell from 97% in 1900 to 60% in 2008, while the shares of plastic and bitumen increased to 16% and 22%, respectively. The rate of gross carbon sequestration in socioeconomic stocks increased from 17 MtC yr−1 in 1900 to a maximum of 247 MtC yr−1 in 2007, corresponding to 2.2%–3.4% of global fossil-fuel-related carbon emissions. We conclude that while socioeconomic carbon stocks are not negligible, their growth over time is not a major climate change mitigation option and there is an only modest potential to mitigate climate change by the increase of socioeconomic carbon stocks."

Citation: Christian Lauk et al 2012 Environ. Res. Lett. 7 034023 doi:10.1088/1748-9326/7/3/034023.


Natural variability and mankind warmed sea surface which played vital role in extreme climate events of 2010

Climate extremes and climate change: The Russian heat wave and other climate extremes of 2010 - Trenberth & Fasullo (2012)

Abstract: "A global perspective is developed on a number of high impact climate extremes in 2010 through diagnostic studies of the anomalies, diabatic heating, and global energy and water cycles that demonstrate relationships among variables and across events. Natural variability, especially ENSO, and global warming from human influences together resulted in very high sea surface temperatures (SSTs) in several places that played a vital role in subsequent developments. Record high SSTs in the Northern Indian Ocean in May 2010, the Gulf of Mexico in August 2010, the Caribbean in September 2010, and north of Australia in December 2010 provided a source of unusually abundant atmospheric moisture for nearby monsoon rains and flooding in Pakistan, Colombia, and Queensland. The resulting anomalous diabatic heating in the northern Indian and tropical Atlantic Oceans altered the atmospheric circulation by forcing quasi-stationary Rossby waves and altering monsoons. The anomalous monsoonal circulations had direct links to higher latitudes: from Southeast Asia to southern Russia, and from Colombia to Brazil. Strong convection in the tropical Atlantic in northern summer 2010 was associated with a Rossby wave train that extended into Europe creating anomalous cyclonic conditions over the Mediterranean area while normal anticyclonic conditions shifted downstream where they likely interacted with an anomalously strong monsoon circulation, helping to support the persistent atmospheric anticyclonic regime over Russia. This set the stage for the “blocking” anticyclone and associated Russian heat wave and wild fires. Attribution is limited by shortcomings in models in replicating monsoons, teleconnections and blocking."

Citation: Trenberth, K. E., and J. T. Fasullo (2012), Climate extremes and climate change: The Russian heat wave and other climate extremes of 2010, J. Geophys. Res., 117, D17103, doi:10.1029/2012JD018020.


You can measure also other things from tree rings than width to estimate temperature

Secular temperature trends for the southern Rocky Mountains over the last five centuries - Berkelhammer & Stott (2012)

Abstract: "Pre-instrumental surface temperature variability in the Southwestern United States has traditionally been reconstructed using variations in the annual ring widths of high altitude trees that live near a growth-limiting isotherm. A number of studies have suggested that the response of some trees to temperature variations is non-stationary, warranting the development of alternative approaches towards reconstructing past regional temperature variability. Here we present a five-century temperature reconstruction for a high-altitude site in the Rocky Mountains derived from the oxygen isotopic composition of cellulose (δ18Oc) from Bristlecone Pine trees. The record is independent of the co-located growth-based reconstruction while providing the same temporal resolution and absolute age constraints. The empirical correlation between δ18Oc and instrumental temperatures is used to produce a temperature transfer function. A forward-model for cellulose isotope variations, driven by meteorological data and output from an isotope-enabled General Circulation Model, is used to evaluate the processes that propagate the temperature signal to the proxy. The cellulose record documents persistent multidecadal variations in δ18Oc that are attributable to temperature shifts on the order of 1°C but no sustained monotonic rise in temperature or a step-like increase since the late 19th century. The isotope-based temperature history is consistent with both regional wood density-based temperature estimates and some sparse early instrumental records."

Citation: Berkelhammer, M. and L. D. Stott (2012), Secular temperature trends for the southern Rocky Mountains over the last five centuries, Geophys. Res. Lett., 39, L17701, doi:10.1029/2012GL052447.

Negative climate change effects on Arctic thecosomes might show up well before ocean acidification effects

Synergistic effects of ocean acidification and warming on overwintering pteropods in the Arctic - Lischka & Riebesell (2012)

Abstract:"Ocean acidification and warming will be most pronounced in the Arctic Ocean. Aragonite shell-bearing pteropods in the Arctic are expected to be among the first species to suffer from ocean acidification. Carbonate undersaturation in the Arctic will first occur in winter and because this period is also characterized by low food availability, the overwintering stages of polar pteropods may develop into a bottleneck in their life cycle. The impacts of ocean acidification and warming on growth, shell degradation (dissolution), and mortality of two thecosome pteropods, the polar Limacina helicina and the boreal L. retroversa, were studied for the first time during the Arctic winter in the Kongsfjord (Svalbard). The abundance of L. helicina and L. retroversa varied from 23.5 to 120 ind m−2 and 12 to 38 ind m−2, and the mean shell size ranged from 920 to 981 μm and 810 to 823 μm, respectively. Seawater was aragonite-undersaturated at the overwintering depths of pteropods on two out of ten days of our observations. A seven-day experiment (temperature levels: 2 and 7°C, pCO2 levels: 350, 650 (only for L. helicina) and 880 μatm) revealed a significant pCO2 effect on shell degradation in both species, and synergistic effects between temperature and pCO2 for L. helicina. A comparison of live and dead specimens kept under the same experimental conditions indicated that both species were capable of actively reducing the impacts of acidification on shell dissolution. A higher vulnerability to increasing pCO2 and temperature during the winter season is indicated compared with a similar study from fall 2009. Considering the species winter phenology and the seasonal changes in carbonate chemistry in Arctic waters, negative climate change effects on Arctic thecosomes are likely to show up first during winter, possibly well before ocean acidification effects become detectable during the summer season."

Citation: Silke Lischka, Ulf Riebesell, Global Change Biology, DOI: 10.1111/gcb.12020.


Ozone depletion is important factor in lower stratospheric cooling

The signature of ozone depletion on tropical temperature trends, as revealed by their seasonal cycle in model integrations with single forcings - Polvani & Solomon (2012) [FULL TEXT]

Abstract: "The effect of ozone depletion on temperature trends in the tropical lower stratosphere is explored with an atmospheric general circulation model, and directly contrasted to the effect of increased greenhouse gases and warmer sea surface temperatures. Confirming and extending earlier studies we find that, over the second half of the 20th Century, the model's lower-stratospheric cooling caused by ozone depletion is several times larger than that induced by increasing greenhouse gases. Moreover, our model suggests that the response to different forcings is highly additive. Finally we demonstrate that when ozone depletion alone is prescribed in the model, the seasonal cycle of the resultant cooling trends in the lower stratosphere is quite similar to that recently reported in satellite and radiosonde observations: this constitutes strong, new evidence for the key role of ozone depletion on tropical lower-stratospheric temperature trends."

Citation: Polvani, L. M., and S. Solomon (2012), The signature of ozone depletion on tropical temperature trends, as revealed by their seasonal cycle in model integrations with single forcings, J. Geophys. Res., 117, D17102, doi:10.1029/2012JD017719.


Causal decoupling between total solar irradiance and global temperature has appeared since 1960s

Evidence of recent causal decoupling between solar radiation and global temperature - Pasini et al. (2012) [FULL TEXT]

Abstract: "The Sun has surely been a major external forcing to the climate system throughout the Holocene. Nevertheless, opposite trends in solar radiation and temperatures have been empirically identified in the last few decades. Here, by means of an inferential method—the Granger causality analysis—we analyze this situation and, for the first time, show that an evident causal decoupling between total solar irradiance and global temperature has appeared since the 1960s."

Citation: Antonello Pasini et al 2012 Environ. Res. Lett. 7 034020, doi:10.1088/1748-9326/7/3/034020.


Ice winter severity index in western Baltic region is modulated by solar activity

Solar forcing on the ice winter severity index in the western Baltic region - Leal-Silv & Velasco Herrera (2012)

Abstract: "The Sun is the fundamental energy sources of the Earth's climate and therefore its variations can contribute to natural climate variations. In the present work we study the variability of ice winter severity index in the Baltic Sea since the 15th century and its possible connection with solar activity, based in a new method for finding and measuring amplitude-phase cross-frequency coupling in time series with a low signal/noise ratio, we suggests that the ice winter severity index in the Baltic Sea is modulated by solar activity and solar motion in several frequency bands during the last 500 yrs. According to our model a strong coupling between the decadal periodicity in the ice winter severity index time series and the secular periodicity of solar activity is present. We found that the ice winter severity index is strongly modulated by solar activity at the decadal periodicity. We also found that the 180 year periodicity of the Barycentre motion modulates the amplitudes of the decadal periodicity of solar activity and the Ice winter severity index. This method represents a useful tool for study the solar-terrestrial relationships."

Citation: M.C. Leal-Silv, V.M. Velasco Herrera, Journal of Atmospheric and Solar-Terrestrial Physics, http://dx.doi.org/10.1016/j.jastp.2012.08.010.


Transition to shrub-dominated Arctic may lead to net C loss if soil temperatures rise

Interactions among shrub cover and the soil microclimate may determine future Arctic carbon budgets - Cahoon et al. (2012)

Abstract: "Arctic and Boreal terrestrial ecosystems are important components of the climate system because they contain vast amounts of soil carbon (C). Evidence suggests that deciduous shrubs are increasing in abundance, but the implications for ecosystem C budgets remain uncertain. Using midsummer CO2 flux data from 21 sites spanning 16° of latitude in the Arctic and Boreal biomes, we show that air temperature explains c. one-half of the variation in ecosystem respiration (ER) and that ER drives the pattern in net ecosystem CO2 exchange across ecosystems. Woody sites were slightly stronger C sinks compared with herbaceous communities. However, woody sites with warm soils (> 10 °C) were net sources of CO2, whereas woody sites with cold soils (< 10 °C) were strong sinks. Our results indicate that transition to a shrub-dominated Arctic will increase the rate of C cycling, and may lead to net C loss if soil temperatures rise."

Citation: Sean M. P. Cahoon, Patrick F. Sullivan, Gaius R. Shaver, Jeffrey M. Welker, Eric Post, Ecology Letters, DOI: 10.1111/j.1461-0248.2012.01865.x.


Open access database of grape harvest dates for climate research

An open-access database of grape harvest dates for climate research: data description and quality assessment - Daux et al. (2012) [FULL TEXT]

Abstract: "We present an open-access dataset of grape harvest dates (GHD) series that has been compiled from international, French and Spanish literature and from unpublished documentary sources from public organizations and from wine-growers. As of June 2011, this GHD dataset comprises 380 series mainly from France (93% of the data) as well as series from Switzerland, Italy, Spain and Luxemburg. The series have variable length (from 1 to 479 data, mean length of 45 data) and contain gaps of variable sizes (mean ratio of observations/series length of 0.74). The longest and most complete ones are from Burgundy, Switzerland, Southern Rhône valley, Jura and Ile-de-France. The most ancient harvest date of the dataset is in 1354 in Burgundy. The GHD series were grouped into 27 regions according to their location, to geomorphological and geological criteria, and to past and present grape varieties. The GHD regional composite series (GHD-RCS) were calculated and compared pairwise to assess their reliability assuming that series close to one another are highly correlated. Most of the pairwise correlations are significant (p-value < 0.001) and strong (mean pairwise correlation coefficient of 0.58). As expected, the correlations tend to be higher when the vineyards are closer. The highest correlation (R = 0.91) is obtained between the High Loire Valley and the Ile-de-France GHD-RCS. The strong dependence of the vine cycle on temperature and, therefore, the strong link between the harvest dates and the temperature of the growing season was also used to test the quality of the GHD series. The strongest correlations are obtained between the GHD-RCS and the temperature series of the nearest weather stations. Moreover, the GHD-RCS/temperature correlation maps show spatial patterns similar to temperature correlation maps. The stability of the correlations over time is explored. The most striking feature is their generalised deterioration at the late 19th–early 20th century. The possible effects on GHD of the phylloxera crisis, which took place at this time, are discussed. The median of all the standardized GHD-RCS was calculated. The distribution of the extreme years of this general series is not homogenous. Extremely late years all occur during a two-century long time window from the early 17th to the early 19th century, while extremely early years are frequent during the 16th and since the mid-19th century."

Citation: Daux, V., Garcia de Cortazar-Atauri, I., Yiou, P., Chuine, I., Garnier, E., Le Roy Ladurie, E., Mestre, O., and Tardaguila, J.: An open-access database of grape harvest dates for climate research: data description and quality assessment, Clim. Past, 8, 1403-1418, doi:10.5194/cp-8-1403-2012, 2012.


CLASSIC OF THE WEEK: Ross (1854)

On the Effect of the Pressure of the Atmosphere on the Mean Level of the Ocean - Ross (1854) [FULL TEXT]

Abstract: No abstract.

Citation: James Clark Ross, Philosophical Transactions of the Royal Society of London, Vol. 144, (1854) (pp. 285-296).

This is a cross-post from AGW Observer. When each paper is published, it is notified in AGW Observer Facebook page and Twitter page. At least some of these are also retweeted in Skeptical Science Twitter page. Here's the archive for the research papers of previous weeks. If this sort of thing interests you, be sure to check out A Few Things Illconsidered. They also have a weekly posting containing lots of links to new research and other climate related news.

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Comments

Comments 1 to 13:

  1. And the graph harvest dates show... a [hic] hockey stick.
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  2. Great papers Ari!

    Willie Soon needs to read Pasini et al. (2012) ;)

    NIce to see that Trenberth and Fasullo put an end to the speculation about the Russian heat wave and Pakistan floods. Weather on steroids.

    And to compliment/corroborate Hansen et al's recent work, researchers find that exceptionally warm temperatures over Europe are increasing in frequency.
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  3. Does that wine data cover English exports during the Medieval Warm Period? :))
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  4. The link to the text of Polvani and Solomon isn't working for me. The following link does:

    http://www.columbia.edu/~lmp/paps/polvani+solomon-JGR-2012.pdf
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  5. Re "socioeconomic carbon sinks," I wonder if we could bribe our way out of this problem by promising to continue paying hydrocarbon companies for their product, converting it to polyethylene* and then reburying instead of burning it? I'm fairly sure we'd see a large segment of climate change denial wither away if such an agreement were made. A pragmatic arrangement, sort of like "Danegeld."

    Various thermodynamic problems with that, I suppose, unless we used solar steam generators for the PE production process.

    Also, would it be ethical to bribe our way out of planetary destruction?

    *Nature's Plastic!
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  6. Doug, we were warned.... Just one word

    >;-/
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  7. Yes, our salvation undoubtedly lies in Tupperware, lots of it. We'll need the UN world government to enforce purchases but that can easily be woven into Agenda 21. Anybody found cracking PE and attempting to make moonshine go-juice can be sent for a "moon landing," heh-heh-heh.
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  8. Link to the full text of Polvani and Solomon fixed, thanks. :)
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  9. What about these news here?

    http://www.washingtontimes.com/news/2012/sep/6/global-warming-fanatics-take-note/#ixzz25u4FCzsb

    Is there an article which helps to put that into context or is this really new stuff to consider?
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  10. the Lucas-Paper of JGR produces empty pages after page 3 ...
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  11. @ Falkenherz at 01:13 AM on 12 September, 2012 re the Washington Times article

    "Pictures like these cannot be drawn for temperature and CO2 concentration." "In 2005, one of us demonstrated a surprisingly strong correlation between solar radiation and temperatures in the Arctic over the past 130 years." "The evidence in BEST’s own data and in other data we have analyzed is consistent with the hypothesis that the sun causes climate change..."

    Bull Shit.



    I don't know what sort of fancy mathturbation they went through to show rising TSI during the satellite era on their graph (MSPaint? or "we used a powerful industry standard visual information processing package[Photoshop] to process the data"), and the WT article notes only that the publication was in 2005 but doesn't cite it. Where's the peer reviewed science that shows rising TSI between 1980 and 2012? TSI is just barely above previous solar cycle minima and the long term trend, but this year has broken all measures of Arctic ice melt. If some college dropout dude on a blog(that would be me) can show that their central premise - "it's the sun, not CO2" - is a lie with a few minutes on the web, what do you trust about ANYTHING else they have to say?
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    Moderator Response: [RH] Fixed image width.
  12. Hii guys. Thanks for the posting Ari!
    Can someone please interpret the Berkelhammer & stott paper re tree growth ring data above? The terminology was above my head!
    Thanks
    Adrian
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  13. @chookmustard
    The authors were concerned that tree ring WIDTH data at their site may not be a good indicator of past temperatures due to a type of "divergence problem" in which the PROXY (the indirect indicator of the measure/driver sought for: ring width) changes its relationship to the driver (temperature) over time. So they tested to find a potentially better proxy, here isotopic oxygen, or 18O. 18O (the delta just means that 18O is measured relative to a common standard, i.e. something everyone uses, so that data can be easily compared across studies) in water equilibrates with 18O in plant internal CO2, and is stored in cellulose as a result of photosynthesis, the main polymer of wood, and changes in response to its availability in "source water", usually from precipitation, which at this site (and many others) is correlated with temperature. As this is a double step from proxy to driver, the authors made sure they understood the underlying uncertainty of their method, and its skill, aka the accuracy of using cellulose-18O to determine past temperature at this site. They found that their methodology seems to work fine. It shows consistency with another proxy record, tree ring wood density, but divergence from the tree ring width proxy. The divergence appears around mid 19th century and the authors speculate about a seasonal temperature change (longterm stability of summer temperatures, driving the 18O signal, vs. changing spring conditions, driving tree ring width) as a possible reason for the observed divergence.

    Hope this helps.
    0 0

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