AGW Observer

Observations of anthropogenic global warming

New research from last week 41/2010

Posted by Ari Jokimäki on October 18, 2010

Here is the new research published last week. I’m not including everything that was published but just some papers that got my attention. Those who follow my Facebook page (and/or Twitter) have already seen most of these, as I post these there as soon as I write them. Here, I’ll just put them out in one batch. Sometimes I might also point out to some other news as well, but the new research will be the focus here. By the way, if this sort of thing interests you, be sure to check out A Few Things Illconsidered, they have a weekly posting containing lots of links to new research and other climate related news.

Published last week:

– An effort to homogenize the radiosonde humidity records has been made in a new study using new approach. They describe the resulting tropospheric humidity data set: “The adjusted daily DPD has much smaller and spatially more coherent trends during 1973–2008 than the raw data. It implies only small changes in relative humidity in the lower and middle troposphere.” Also noteworthy is: “The DPD adjustment yields a different pattern of change in humidity parameters compared to the apparent trends from the raw data. The adjusted estimates show an increase in tropospheric water vapor globally”
Citation: Aiguo Dai and Junhong Wang, Peter W. Thorne, David E. Parker, Leopold Haimberger, Xiaolan L. Wang, Journal of Climate 2010, doi: 10.1175/2010JCLI3816.1. [abstract]

– A new study looks at temperature proxies based on pollen and tree-rings. Pollen data is commonly thought to be a long term proxy and not so good short term proxy while tree-rings are thought to capture short term variations better than long term variations. The new study uses proxies from high-latitude Europe (probably some from my home country Finland!). The pollen and tree-ring data are compared and it turns out they compare well in long term variability. They show similar variability on centennial and longer scales. The resulting reconstruction is described: “Over longer intervals, our new proxy-fusions cover the climatic reversals of the Medieval Climate Anomaly (during the 10th to 13th centuries), Little Ice Age (during the 14th to 19th centuries), and 20th century warming. The warmest spells occurred in association with the Medieval Climate Anomaly and during the 20th century. The coolest intervals occurred in relation to Little Ice Age conditions. The new reconstructions show that decadal temperature amplitude has been approximately 2.5 °C in the past and thus considerably larger than inferred from spatially large-scale estimates of temperature anomalies.”
Citation: Samuli Helama, Heikki Seppä, H. John B. Birks, and Anne E. Bjune, Reconciling pollen-stratigraphical and tree-ring evidence for high- and low-frequency temperature variability in the past millennium, Quaternary Science Reviews, 2010, doi:10.1016/j.quascirev.2010.09.012. [abstract]

– New research article says that the existing explanation for the extinction of Neanderthals are not satisfactory: “The two main factors currently proposed are the arrival of a modern human competitor and/or the aptitude of the Neanderthals to survive rapidly changing climatic conditions. None of these hypotheses is fully satisfactory because the Neanderthals experienced other large climatic changes and the duration of overlap of the two populations remains largely unknown and even uncertain.” The article points out that two geomagnetic events are synchronous with the Neandertal extinction; the Laschamp event and the Mono Lake event. These were the most dramatic events in the history of Neanderthals. The article explains why the events would have been important in the extinction: “During this period the geomagnetic field strength was considerably reduced and the shielding efficiency of the magnetosphere lowered, leaving energetic particles reach latitudes as low as 30°. The enhanced flux of high-energy protons (linked to solar activity) into the atmosphere yielded significant ozone depletion down to latitudes of 40–45°. A direct consequence was an increase of the UV-B radiations at the surface which might have reached at least 15–20% in Europe with significant impacts on health of human populations. We suggest that these conditions, added to some other factors, contributed to the demise of Neanderthal population.”
Citation: Jean-Pierre Valet and Hélène Valladas, The Laschamp-Mono lake geomagnetic events and the extinction of Neanderthal: A causal link or a coincidence?, Quaternary Science Reviews, 2010, doi:10.1016/j.quascirev.2010.09.010. [abstract]

– New study has made an effort to constrain climate sensitivity. They point out that current range of 2 – 4.5 K has lot of uncertainty. They describe their methods: “Simple indices of spatial radiation patterns are used here to establish a relationship between an observable radiative quantity and the equilibrium climate sensitivity. The indices are computed for the CMIP3 multi-model data set and offer a possibility to constrain climate sensitivity by considering radiation patterns in the climate system.” They find high correlations between the indices and climate sensitivity in certain cases. Resulting climate sensitivities between different data sets are: CERES – 2.7 to 4 K, ERBE (the dataset Lindzen & Choi used to claim negative feedback) – 1.7 to 3.8 K, ISCCP – 2.9 to 3.7 K, MERRA – 2.8 to 4.1 K, JRA25 – 3 to 4.2 K, ERA-Interim – 2.7 to 3.9 K, ERA-40 – 3 to 4 K, NCEP – 3.1 to 4.7 K. Conclusion: “For the aggregation of the reference datasets, the climate sensitivity is unlikely to be below 2.9 K within the framework of our study, whereas values exceeding 4.5 K cannot be excluded from our analysis.”
Citation: Markus Huber, Irina Mahlstein and Martin Wild, John Fasullo, Reto Knutti, Constraints on climate sensitivity from radiation patterns in climate models, Journal of Climate 2010, doi: 10.1175/2010JCLI3403.1. [abstract]

– This one was mentioned in the paper that was just published by the Science (the one about “climate control knob”). Here they determine the relative contributions of greenhouse gases and the result is 50 % from water vapor, 25 % from clouds, 20 % from CO2, and the contribution from other GHGs is small. The abstract mentions in the end: “All other absorbers play only minor roles. In a doubled CO2 scenario, this allocation is essentially unchanged, even though the magnitude of the total greenhouse effect is significantly larger than the initial radiative forcing, underscoring the importance of feedbacks from water vapor and clouds to climate sensitivity.”
Citation: Schmidt, G. A., R. A. Ruedy, R. L. Miller, and A. A. Lacis (2010), Attribution of the present-day total greenhouse effect, J. Geophys. Res., 115, D20106, doi:10.1029/2010JD014287. [abstract, full text, GISS page with research brief and news release]

– Dessler & Davis have studied the situation with tropospheric humidity. There is a situation that while generally a positive water vapor feedback is observed, the NCEP/NCAR reanalysis shows long term water vapor feedback to be negative especially in tropics. In this new study, five different reanalyses are being studied together. It is found that all five reanalyses: “…unanimously agree that specific humidity generally increases in response to short-term climate variations (e.g., El Niño).” However, in long term analysis, NCEP/NCAR reanalysis shows decreasing tropical mid and upper tropospheric specific humidity in response to decadal warming, but all other four reanalyses show increasing tropical mid and upper tropospheric specific humidity in response to decadal warming. Conclusion: “We conclude from this that it is doubtful that these negative long-term specific humidity trends in the NCEP/NCAR reanalysis are realistic for several reasons.” First reason is that newer reanalyses have improved features specifically for making the long term performance more accurate, so older reanalyses, like NCEP/NCAR are likely to be more inaccurate in long term trends. Second reason is that NCEP/NCAR is the only reanalysis that doesn’t use satellite measurements in addition to radiosonde measurements. And final two points: “Third, the NCEP/NCAR reanalysis exhibits a large bias in tropical upper tropospheric specific humidity. And finally, we point out that there exists no theoretical support for having a positive short-term water vapor feedback and a negative long-term one.”
Citation: Dessler, A. E., and S. M. Davis (2010), Trends in tropospheric humidity from reanalysis systems, J. Geophys. Res., 115, D19127, doi:10.1029/2010JD014192. [abstract]

“Boreal lakes are known to be supersaturated with CO2 and to be significant sources of CO2 to the atmosphere”, the abstract of a new research article starts. Small boreal streams have been studied and they apparently are even moire supersaturated with carbon dioxide, so the small boreal streams are also a carbon dioxide emission source. The emissions from them are surprisingly large: “Small boreal streams account for an annual (ice-free seasons) average of 8.0% and a seasonal high of 34.4% of the total CO2 evaded from streams and lakes.” Emissions are greatest in summer from the streams.
Citation: Koprivnjak, J.-F., P. J. Dillon, and L. A. Molot (2010), Importance of CO2 evasion from small boreal streams, Global Biogeochem. Cycles, 24, GB4003, doi:10.1029/2009GB003723. [abstract]

– New research article reports an analysis of the timing when ocean acidification causes corrosive conditions to aragonite using species. Earlier this condition has been expected to begin in 2015. By using both observations and models, researchers found that sea ice cover and deep-water entrainment during winter causes the ocean to take in less carbon dioxide than expected. Their conclusion: “This means that instead of corrosive ‘acidified’ waters beginning as early as the winter of 2015, anthropogenic CO2 disequilibrium delays its onset by up to 30 years, giving this Antarctic marine ecosystem a several decade reprieve to corrosive conditions.”
Citation: McNeil, B. I., A. Tagliabue, and C. Sweeney (2010), A multi-decadal delay in the onset of corrosive ‘acidified’ waters in the Ross Sea of Antarctica due to strong air-sea CO2 disequilibrium, Geophys. Res. Lett., 37, L19607, doi:10.1029/2010GL044597. [abstract]

– New study has compared model simulated extreme temperatures to observed extreme temperatures both regionally and globally. Extreme temperatures here mean annual minimums and maximums of daily minimum and maximum temperatures. The results suggest that the anthropogenic forcing can be seen in the extreme temperatures globally and regionally in many places over land areas. Detection of anthropogenic forcing seems to be strongest in annual maximum of daily minimum temperatures. Minimum extremes have changed from events that happened once every 20 years in 1960’s to similar events happening now once in over 30 years. Maximum extremes show rather different change though: “In contrast, waiting times for circa 1960s 20-year extremes of annual maximum daily minimum and daily maximum temperatures are estimated to have decreased to less than 10 and 15 years respectively.”
Citation: Francis W. Zwiers, Xuebin Zhang, Yang Feng, Anthropogenic Influence on Long Return Period Daily Temperature Extremes at Regional Scales, Journal of Climate, 2010, doi: 10.1175/2010JCLI3908.1. [abstract]

– The urban heat island effect and global warming have warmed up the groundwater below the cities. A new study looks how much heat there actually is: “Detailed groundwater temperature measurements in Cologne (Germany) and Winnipeg (Canada) reveal high subsurface temperature distributions in the centers of both cities and indicate a warming trend of up to 5 °C.” This might have interesting propects: “The results show, for example, that, by decreasing the 20 m thick urban aquifer’s temperature by 2 °C, the amount of extractable geothermal energy beneath Cologne is 2.5 times the residential heating demand of the whole city. The geothermal potential in other cities such as Shanghai and Tokyo is shown to supply heating demand even for decades.”
Citation: Ke Zhu, Philipp Blum, Grant Ferguson, Klaus-Dieter Balke and Peter Bayer, The geothermal potential of urban heat islands, Environmental Research Letters, 2010, Volume 5, Number 4, doi: 10.1088/1748-9326/5/4/044002. [abstract]

– New study reports direct measurements of the contribution of continental ice and water to the global sea level. GRACE satellite data was used to measure mass exchange between land and ocean. Conclusion: “We estimate that the total ice and water mass loss from the continents is causing global mean sea-level to rise by 1.0 ± 0.4 mm/yr. Isolating the ice and hydrological signals, we find that the former is the sole net contributor to the global mean, while the latter dominates regional RSL changes in many coastal areas.”
Citation: Riva, R. E. M., J. L. Bamber, D. A. Lavallée, and B. Wouters (2010), Sea-level fingerprint of continental water and ice mass change from GRACE, Geophys. Res. Lett., 37, L19605, doi:10.1029/2010GL044770. [abstract]

– Using hydrodynamic and carbon model, a new study has investigated the influence of hurrican passage to air sea carbon dioxide exchange: “The results showed that the sea surface temperature cooling was the dominant cause of the decrease of surface pCO2, while the entrainment of water with higher CO2 levels partially offset the cooling-induced decrease.” Hurricane effect was rather wide: “The impact of the hurricane on the local air-sea CO2 exchange extended to about 100 km on both sides of the hurricane track.” On the amount of carbon dioxide: “The whole passage of Hurricane Frances was estimated to have caused a CO2 efflux of about 3.504–10.363 Tg (1 Tg = 1012 g) C from ocean to the atmosphere. Globally, hurricanes in 2004 were estimated to have released a CO2 efflux of 0.047–0.141 Pg (1 Pg = 1015 g) C in total when extrapolating from Hurricane Frances. Under our assumptions, the CO2 efflux caused by the passages of global hurricanes should have increased by about 71.2%–75.0% in past decades.”
Citation: Huang, P., and J. Imberger (2010), Variation of pCO2 in ocean surface water in response to the passage of a hurricane, J. Geophys. Res., 115, C10024, doi:10.1029/2010JC006185. [abstract]

– A PNAS article to be published next week says that a slow-down of population growth could decrease carbon dioxide emissions: “The study showed that a slowing of population growth, following one of the slower growth paths considered plausible by demographers at the United Nations, could contribute to significantly reducing greenhouse gas emissions. The researchers found that such slow growth paths by 2050 could account for 16 to 29 percent of the emissions reductions thought necessary to keep global temperatures from causing serious impacts.” Another factor is increasing urbanization which according to this study increases emissions because urban citizens tend to produce and consume more. Population aging is a factor that decreases emissions because older people are less productive due to low percentage of them participating in labor force.
Source: Population trends: Another influence on climate change – UCAR news

– A study using chemistry climate model looked if climate change will increase the ozone depletion. They find some increase in certain years but in other years there are compensating effects. Overall climate change doesn’t seem to have much effect to ozone depletion. “In years of strong geomagnetic activity, similar to that observed in 2003, an additional polar ozone loss of up to 0.4 μmol/mol at 5 hPa is found in the Southern Hemisphere. However, this would be approximately compensated by an ozone enhancement originating from a stronger poleward transport of ozone from lower latitudes caused by a strengthened Brewer-Dobson circulation, as well as by slower photochemical ozone loss reactions in a stratosphere cooled by risen greenhouse gas concentrations. In the Northern Hemisphere the EEP NOx effect appears to lose importance due to the different nature of the climate-change induced circulation changes.”
Citation: Baumgaertner, A. J. G., Jöckel, P., Dameris, M., and Crutzen, P. J.: Will climate change increase ozone depletion from low-energy-electron precipitation?, Atmos. Chem. Phys., 10, 9647-9656, doi:10.5194/acp-10-9647-2010, 2010. [abstract, full text]

– New research article reports of an analysis of the seasonal oscillation in USA surface temperatures. They got a surprising result: “We found the presence of an orbit-climate relationship on time scales remarkably shorter than the Milankovitch period {relat…ed to the nutational forcing}. The relationship manifests itself through occasional destabilization of the phase of the seasonal component due to the local changing of balance between direct insolation and the net energy received by the Earth. Quite surprisingly, we found that the local intermittent dynamics is modulated by a periodic component of about 18.6 yr due to the nutation of the Earth, which represents the main modulation of the Earth’s precession.” It has an effect to Earth seasons: “The global effect in the last century results in a cumulative phase-shift of about 1.74 days towards earlier seasons, in agreement with the phase shift expected from the Earth’s precession.”
Citation: Vecchio, A., Capparelli, V., and Carbone, V.: The complex dynamics of the seasonal component of USA’s surface temperature, Atmos. Chem. Phys., 10, 9657-9665, doi:10.5194/acp-10-9657-2010, 2010. [abstract, full text]

– Measurements of carbon related parameters from the ocean in Canary islands. “We have evaluated the ESTOC (European Station for Time series in the Ocean at the Canary islands) observations of measured pH (total scale at 25 °C) and total alkalinity plus computed total dissolved inorganic carbon concentration (CT) from 1995 to 2004 for surface and deep waters, by following all changes in response to increasing atmospheric carbon dioxide. The observed values for the surface partial pressure of CO2 from 1995 to 2008 were also taken into consideration.” Results: “CT at constant salinity, NCT, increased at a rate of 0.85 μmol kg−1 yr−1 in the mixed layer, linked to an fCO2 increase of 1.7±0.7 μatm yr−1 in both the atmosphere and the ocean. Consequently, the mixed layer at ESTOC site has also become more acidic, −0.0017±0.0003 units yr−1, whereas the carbonate ion concentrations and CaCO3 saturation states have also decreased over time. NCT increases at a rate of 0.53, 0.49 and 0.40 μmol kg−1 yr−1 at 300, 600, and 1000 m, respectively.” and: “The total column inventory of anthropogenic CO2 for the decade was 66±3 mol m−2. A model fitting indicated that the column inventory of CANT increased from 61.7 mol m−2 in the year 1994 to 70.2 mol m−2 in 2004.”
Citation: González-Dávila, M., Santana-Casiano, J. M., Rueda, M. J., and Llinás, O.: The water column distribution of carbonate system variables at the ESTOC site from 1995 to 2004, Biogeosciences, 7, 3067-3081, doi:10.5194/bg-7-3067-2010, 2010. [abstract, full text]

– Addition of new fully automatic ground-based FTIR system for GHG total column measurements in tropics. There’s no Earth-shattering news here, but I just wanted to use this new research article to highlight one method to measure GHG-concentrations in the atmosphere. This new system uses Fourier Transform Spectrometer (FTIR) to measure effects of greenhouse gases to solar radiation. The incoming sunlight has energy also in infrared portion of the electromagnetic spectrum. Greenhouse gases have characteristic absorption lines in infrared so their effect can be measured from direct sunlight with proper instruments. The research article explains it further: “From the difference of the known solar spectrum from space and the measured solar spectrum after passing through the atmosphere, the total column of gases like CO2, CH4 and many others can be calculated.” The total column calculation additionally needs knowledge of the total dry air column which “can be derived either from surface pressure or from the measured O2 total column”. The point of this study is to introduce a new measurement system which will be installed to the tropics where existing measurement network has been sparse. “First results of total column measurements at Jena, Germany show that the instrument works well and can provide parts of the diurnal as well as seasonal cycle for CO2.”
Citation: Rayner, P. J., M. R. Raupach, M. Paget, P. Peylin, and E. Koffi (2010), A new global gridded data set of CO2 emissions from fossil fuel combustion: Methodology and evaluation, J. Geophys. Res., 115, D19306, doi:10.1029/2009JD013439. [abstract, full text]


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