AGW Observer

Observations of anthropogenic global warming

New research from last week 20/2012

Posted by Ari Jokimäki on May 21, 2012

This week I have some bad news for you. Late 20th century warming was not natural event in Australasia, but it seems that we did it with our fossil fuels. When we started warming up the Earth with carbon dioxide from fossil fuels, I guess we just didn’t realize that climate sensitivity is bigger for that than for solar forcing. We see that for example in tropospheric water vapor increase and in oceanic warming. Summer monsoon is also weakening and making air pollution situation even worse. Humans might be affected too, as has happened during past climate changes.

So what do we do? We start using biofuels, but that then seems to destroy stratospheric ozone, which protects us from solar UV radiation. El Niño is of no help, because it just mixes up the carbon dioxide in the atmosphere. We could try to see if we can identify tree rings in Ethiopia, but that might be just fun recreational activity and might not actually help. Perhaps we should just hope that climate sensitivity is not that bad. After all, there is uncertainty in cloud feedback, so it might be that we only get 2+ Kelvins of warming. Perhaps best thing to do is to sit back, read some more studies next week, and hope they come up with a plan for us, right?


Transition from fossil fuels to biofuels might be bad idea from ozone layer perspective

Impacts of the production and consumption of biofuels on stratospheric ozone – Revell et al. (2012)

Abstract: “Biofuels are becoming increasingly popular sources of renewable energy as economic pressures and environmental consequences encourage the use of alternatives to fossil fuels. However, growing crops destined for use as biofuels incurs large N2O emissions associated with the use of nitrogen-based fertilizers. Besides being a greenhouse gas, N2O is also the primary source of stratospheric NOx (NO + NO2) which leads to stratospheric ozone depletion. In this paper, the potential effects on the ozone layer of a large-scale shift away from fossil fuel use to biofuels consumption over the 21st century are examined. Under such a scenario, global-mean column ozone decreases by 2.6 DU between 2010 and 2100 in contrast to a 0.7 DU decrease under a control simulation (the IPCC SRES B1 scenario for greenhouse gases) and a 9.1 DU increase under the more commonly used SRES A1B scenario. Two factors cause the decrease in ozone in the biofuels simulation: 1) large N2O emissions lead to faster rates of the ozone-depleting NOx cycles and; 2) reduced CO2 emissions (due to less fossil fuel burning) lead to relatively less stratospheric cooling over the 21st century, which decreases ozone abundances. Reducing CO2 emissions while neglecting to reduce N2O emissions could therefore be damaging to the ozone layer.”

Citation: Revell, L. E., G. E. Bodeker, P. E. Huck, and B. E. Williamson (2012), Impacts of the production and consumption of biofuels on stratospheric ozone, Geophys. Res. Lett., 39, L10804, doi:10.1029/2012GL051546.


Late 20th century warming was unusual and outside natural variability in Australasia during last millenium

Evidence of unusual late 20th century warming from an Australasian temperature reconstruction spanning the last millennium – Gergis et al. (2012) [FULL TEXT]

Abstract: “This study presents the first multi-proxy warm season (September-February) temperature reconstruction for the combined land and oceanic region of Australasia (0°S-50°S, 110°E-180°E). We perform a 3000-member ensemble Principal Component Reconstruction (PCR) using 27 temperature proxies from the region. The proxy network explained 69% of the inter-annual variance in the HadCRUT3v SONDJF spatial mean temperature over the 1921-1990 calibration period. Applying eight stringent reconstruction ‘reliability’ metrics identified post A.D. 1430 as the highest quality section of the reconstruction, but also revealed a skilful reconstruction is possible over the full A.D. 1000-2001 period. The average reconstructed temperature anomaly in Australasia during A.D. 1238-1267, the warmest 30-year pre-instrumental period, is 0.09°C (±0.19°C) below 1961-1990 levels. Following peak pre-industrial warmth, a cooling trend culminates in a temperature anomaly of 0.44°C (±0.18°C) below 1961-1990 levels between A.D. 1830-1859. A preliminary assessment of the roles of solar, volcanic, and anthropogenic forcings and natural ocean-atmosphere variability is performed using CSIRO Mk3L model simulations and independent palaeoclimate records. Solar and volcanic forcing does not have a marked influence on reconstructed Australasian temperature variations, which appear to be masked by internal variability. In 94.5% of the 3000-member reconstruction ensemble, there are no other warm periods in the past 1,000 years that match or exceed post-1950 warming observed in Australasia. The unusual 20th century warming cannot be explained by natural variability alone, suggesting a strong influence of anthropogenic forcing in the Australasian region.”

Citation: Joëlle Gergis, Raphael Neukom, Steven J. Phipps, Ailie J. E. Gallant, David J. Karoly, and PAGES Aus2K Project Members, Journal of Climate 2012, doi: http://dx.doi.org/10.1175/JCLI-D-11-00649.1.


Is climate sensitivity less for solar forcing than for carbon dioxide forcing?

Sensitivity of an Earth system climate model to idealized radiative forcing – Andrews et al. (2012)

Abstract: “We diagnose forcing and climate feedbacks in benchmark sensitivity experiments with the new Met Office Hadley Centre Earth system climate model HadGEM2-ES. To identify the impact of newly-included biogeophysical and chemical processes, results are compared to a parallel set of experiments performed with these processes switched off, and different couplings with the biogeochemistry. In abrupt carbon dioxide quadrupling experiments we find that the inclusion of these processes does not alter the global climate sensitivity of the model. However, when the change in carbon dioxide is uncoupled from the vegetation, or when the model is forced with a non-carbon dioxide forcing – an increase in solar constant – new feedbacks emerge that make the climate system less sensitive to external perturbations. We identify a strong negative dust-vegetation feedback on climate change that is small in standard carbon dioxide sensitivity experiments due to the physiological/fertilization effects of carbon dioxide on plants in this model.”

Citation: Andrews, T., M. A. Ringer, M. Doutriaux-Boucher, M. J. Webb, and W. J. Collins (2012), Sensitivity of an Earth system climate model to idealized radiative forcing, Geophys. Res. Lett., 39, L10702, doi:10.1029/2012GL051942.


Updated estimates of world ocean heat content and sea level change

World ocean heat content and thermosteric sea level change (0–2000 m), 1955–2010 – Levitus et al. (2012)

Abstract: “We provide updated estimates of the change of ocean heat content and the thermosteric component of sea level change of the 0–700 and 0–2000 m layers of the World Ocean for 1955–2010. Our estimates are based on historical data not previously available, additional modern data, and bathythermograph data corrected for instrumental biases. We have also used Argo data corrected by the Argo DAC if available and used uncorrected Argo data if no corrections were available at the time we downloaded the Argo data. The heat content of the World Ocean for the 0–2000 m layer increased by 24.0 ± 1.9 × 1022 J (±2S.E.) corresponding to a rate of 0.39 W m−2 (per unit area of the World Ocean) and a volume mean warming of 0.09°C. This warming corresponds to a rate of 0.27 W m−2 per unit area of earth’s surface. The heat content of the World Ocean for the 0–700 m layer increased by 16.7 ± 1.6 × 1022 J corresponding to a rate of 0.27 W m−2 (per unit area of the World Ocean) and a volume mean warming of 0.18°C. The World Ocean accounts for approximately 93% of the warming of the earth system that has occurred since 1955. The 700–2000 m ocean layer accounted for approximately one-third of the warming of the 0–2000 m layer of the World Ocean. The thermosteric component of sea level trend was 0.54 ± .05 mm yr−1 for the 0–2000 m layer and 0.41 ± .04 mm yr−1 for the 0–700 m layer of the World Ocean for 1955–2010.”

Citation: Levitus, S., et al. (2012), World ocean heat content and thermosteric sea level change (0–2000 m), 1955–2010, Geophys. Res. Lett., 39, L10603, doi:10.1029/2012GL051106.


Radiosondes and reanalyses see positive trends in tropospheric water vapor over parts of Arctic

Recent changes in tropospheric water vapor over the Arctic as assessed from radiosondes and atmospheric reanalyses – Serreze et al. (2012) [Presentation material]

Abstract: “Changes in tropospheric water vapor over the Arctic are examined for the period 1979 to 2010 using humidity and temperature data from nine high latitude radiosonde stations north of 70°N with nearly complete records, and from six atmospheric reanalyses, emphasizing the three most modern efforts, MERRA, CFSR and ERA-Interim. Based on comparisons with the radiosonde profiles, the reanalyses as a group have positive cold-season humidity and temperature biases below the 850 hPa level and consequently do not capture observed low-level humidity and temperature inversions. MERRA has the smallest biases. Trends in column-integrated (surface to 500 hPa) water vapor (precipitable water) computed using data from the radiosondes and from the three modern reanalyses at the radiosonde locations are mostly positive, but magnitudes and statistical significance vary widely between sites and seasons. Positive trends in precipitable water from MERRA, CFSR and ERA-Interim, largest in summer and early autumn, dominate the northern North Atlantic, including the Greenland, Norwegian and Barents seas, the Canadian Arctic Archipelago and (on the Pacific side) the Beaufort and Chukchi seas. This pattern is linked to positive anomalies in air and sea surface temperature and negative anomalies in end-of-summer sea ice extent. Trends from ERA-Interim are weaker than those from either MERRA or CFSR. As assessed for polar cap averages (the region north of 70°N), MERRA, CFSR and ERA-Interim all show increasing surface-500 hPa precipitable over the analysis period encompassing most months, consistent with increases in 850 hPa air temperature and 850 hPa specific humidity. Data from all of the reanalyses point to strong interannual and decadal variability. The MERRA record in particular shows evidence of artifacts likely introduced by changes in assimilation data streams. A focus on the most recent decade (2001–2010) reveals large differences between the three reanalyses in the vertical structure of specific humidity and temperature anomalies.”

Citation: Serreze, M. C., A. P. Barrett, and J. Stroeve (2012), Recent changes in tropospheric water vapor over the Arctic as assessed from radiosondes and atmospheric reanalyses, J. Geophys. Res., 117, D10104, doi:10.1029/2011JD017421.


El Niño has an influence to atmospheric carbon dioxide distribution

Influence of El Niño on Mid-tropospheric CO2 from Atmospheric Infrared Sounder and Model – Jiang et al. (2012)

Abstract: “We investigate the influence of El Niño on the mid-tropospheric CO2 from the Atmospheric Infrared Sounder (AIRS) and Model of Ozone and Related Chemical Tracers version 2 (MOZART-2). AIRS mid-tropospheric CO2 data are used to study the temporal and spatial variability of CO2 in response to El Niño. CO2 difference between the Central Pacific and Western Pacific correlates well with the Southern Oscillation Index. To reveal the temporal and spatial variability of El Niño signal in the AIRS mid-tropospheric CO2, a multiple regression method is applied to the CO2 data from September 2002 to February 2011. There is more (less) mid-tropospheric CO2 in the Central Pacific and less (more) mid-tropospheric CO2 in the Western Pacific during El Niño (La Niña) events. Similar results are seen in the MOZART-2 convolved mid-tropospheric CO2, although the El Niño signal in the MOZART-2 is weaker than that in the AIRS data.”

Citation: Xun Jiang, Jingqian Wang, Edward T. Olsen, Maochang Liang, Thomas S. Pagano, Luke L. Chen, Stephen J. Licata, and Yuk L. Yung, Journal of the Atmospheric Sciences 2012, doi: http://dx.doi.org/10.1175/JAS-D-11-0282.1.


Were historical population crises in China related to climate?

A tale of two population crises in recent Chinese history – Lee & Zhang (2012) [FULL TEXT]

Abstract: “The fall of the Ming dynasty in the first half of the 17th century and the Taiping Rebellion from 1851–1864 were two of the most chaotic periods in Chinese history, and each was accompanied by large-scale population collapses. The ‘Kang-Qian Golden Age’ (also known as ‘High Qing’), during which population size expanded rapidly, falls in between the two. Scholars remain divided in their opinions concerning the above alternation of population growth and decline as to whether variations in population size or climate change should be identified as the root cause. In either case, the synergistic impact of population growth and climate change upon population growth dynamics is overlooked. In the present study, we utilized high-resolution empirical data, qualitative survey, statistical comparison and time-series analysis to investigate how the two factors worked synergistically to drive population cycles in 1600–1899. To facilitate our research, we posited a set of simplified pathways for population growth in historical agrarian China. Our results confirm that the interrelation between population growth, climate change and population crises in recent Chinese history basically followed our posited pathways. The recurrences of population crises were largely determined by the combination of population growth and climate change. Our results challenge classic Malthusian/post-Malthusian interpretations and historians’ views of historical Chinese population cycles.”

Citation: Harry F. Lee and David D. Zhang, Climatic Change, 2012, DOI: 10.1007/s10584-012-0490-9.


Trying to see annual tree-rings in permanent growing readiness trees of Ethiopia

Growth dynamics and potential for cross-dating and multi-century climate reconstruction of Podocarpus falcatus in Ethiopia – Krepkowski et al. (2012)

Abstract: “Podocarpus falcatus is an indigenous evergreen conifer species of tropical mountain forests in southeastern Ethiopia, showing potential tree ages of around 500 years. To study the influence of seasonal climate on the growth pattern of P. falcatus, we combined high-resolution electronic dendrometer measurements with wood anatomical investigations of microcores from the outermost stem parts collected in monthly intervals. At any time of the year sufficient rain events are able to cause cambial activity in P. falcatus. This permanent growing readiness leads to irregular wood formation with the formation of intra-annual density fluctuations and missing rings. Wood anatomical studies of microcores collected around the circumference of a mature P. falcatus revealed locally different activity status of the cambium on different lobes of the stem. Tree-ring width measurements of stem disks resulted in tentative tree ages that were confirmed by radiocarbon dating of selected wood samples. Although our efforts to cross-date ring-width series from several stem disks were not successful, further sampling in areas with different rainfall regimes, additional radiocarbon dating and measurements of stable isotopes hopefully would enable the establishment of a multi-century-long tree-ring series for climate reconstruction.”

Citation: Julia Krepkowski, Achim Bräuning, Aster Gebrekirstos, Dendrochronologia, http://dx.doi.org/10.1016/j.dendro.2012.01.001.


Weakening of summer monsoon has increased aerosol concentrations over eastern China

Increases in aerosol concentrations over eastern China due to the decadal-scale weakening of the East Asian summer monsoon – Zhu et al. (2012) [FULL TEXT]

Abstract: “China has been experiencing increased concentrations of aerosols, commonly attributed to the large increases in emissions associated with the rapid economic development. We show by using a chemical transport model driven by the assimilated meteorological fields that the observed decadal-scale weakening of the East Asian summer monsoon also contributed to the increases in aerosols in China. We find that the simulated aerosol concentrations have strong negative correlations with the strength of the East Asian Summer monsoon. Accounting for sulfate, nitrate, ammonium, black carbon, and organic carbon aerosols, the summer surface-layer PM2.5 concentration averaged over eastern China (110°–125°E, 20°–45°N) can be 17.7% higher in the weakest monsoon years than in the strongest monsoon years. The weakening of the East Asian Summer monsoon increases aerosol concentrations mainly by the changes in atmospheric circulation (the convergence of air pollutants) in eastern China.”

Citation: Zhu, J., H. Liao, and J. Li (2012), Increases in aerosol concentrations over eastern China due to the decadal-scale weakening of the East Asian summer monsoon, Geophys. Res. Lett., 39, L09809, doi:10.1029/2012GL051428.


Differences in cloud feedbacks continue to be important contributors to 2.1–4.7 K range of equilibrium climate sensitivity

Forcing, feedbacks and climate sensitivity in CMIP5 coupled atmosphere-ocean climate models – Andrews et al. (2012)

Abstract: “We quantify forcing and feedbacks across available CMIP5 coupled atmosphere-ocean general circulation models (AOGCMs) by analysing simulations forced by an abrupt quadrupling of atmospheric carbon dioxide concentration. This is the first application of the linear forcing-feedback regression analysis of Gregory et al. (2004) to an ensemble of AOGCMs. The range of equilibrium climate sensitivity is 2.1–4.7 K. Differences in cloud feedbacks continue to be important contributors to this range. Some models show small deviations from a linear dependence of top-of-atmosphere radiative fluxes on global surface temperature change. We show that this phenomenon largely arises from shortwave cloud radiative effects over the ocean and is consistent with independent estimates of forcing using fixed sea-surface temperature methods. We suggest that future research should focus more on understanding transient climate change, including any time-scale dependence of the forcing and/or feedback, rather than on the equilibrium response to large instantaneous forcing.”

Citation: Andrews, T., J. M. Gregory, M. J. Webb, and K. E. Taylor (2012), Forcing, feedbacks and climate sensitivity in CMIP5 coupled atmosphere-ocean climate models, Geophys. Res. Lett., 39, L09712, doi:10.1029/2012GL051607.


Observed tropical tropopause cooling might not be statistically significant

How well do we know recent climate trends at the tropical tropopause? – Wang et al. (2012)

Abstract: “The tropical tropopause is a transition layer between the troposphere and stratosphere that influences global climate and atmospheric chemistry. Several studies have reported multidecadal tropical tropopause cooling and have suggested a correlation between observed tropopause temperature and stratospheric water vapor. Our more rigorous examination of the observations shows tropopause trends have greater uncertainty than previously suggested and the cooling may not be statistically significant. We used two approaches to remove time-varying bias effects from cold-point tropopause trends estimated from radiosonde observations. Our results are consistent with expectations from a conceptual model of tropopause changes and could resolve discrepancies between complex climate models and observations.”

Citation: Wang, J. S., D. J. Seidel, and M. Free (2012), How well do we know recent climate trends at the tropical tropopause?, J. Geophys. Res., 117, D09118, doi:10.1029/2012JD017444.


CLASSIC OF THE WEEK: Dobson (1923)

Measurements of the Sun’s Ultra-Violet Radiation and Its Absorption in the Earth’s Atmosphere – Dobson et al. (1923) [FULL TEXT]

Abstract: No abstract. Quote from the paper: “The object of the present work was to obtain, if possible, a long series of measurements of the ultra-violet light radiated by the sun, the atmospheric transmission coefficient for this light and also the amount of ozone in the atmosphere.”

Citation: G. M. B. Dobson, Proc. R. Soc. Lond. A September 1, 1923 104 725 252-271; doi:10.1098/rspa.1923.0107 .


When each paper is published, it is notified in AGW Observer Facebook page and 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.

2 Responses to “New research from last week 20/2012”

  1. witsendnj said

    That does seem like bad news! It must mean that more research is needed.

  2. […] 2012/05/21: AGWObserver: New research from last week 20/2012 […]

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