This chapter should be cited as: Myhre, G., D. Shindell, F.-M. Bréon, W. Collins, J. Fuglestvedt, J. Huang, D. Koch, J.-F. Lamarque, D. Lee, B. Mendoza, T. Nakajima, A. Robock, G. Stephens, T. Takemura and H. Zhang, 2013: Anthropogenic and Natural Radiative Forcing. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. Coordinating Lead Authors: Gunnar Myhre (Norway), Drew Shindell (USA)

Anthropogenic and Natural Radiative Forcing

http://ruby.fgcu.edu/courses/twimberley/envirophilo/wanner.pdf

Mid- to Late Holocene climate change: an overview

Past global climate changes had strong regional expression To elucidate their spatio-temporal pattern, we reconstructed past temperatures for seven continental-scale regions during the past one to two millennia The most coherent feature in nearly all of the regional temperature reconstructions is a long-term cooling trend, which ended late in the nineteenth century At multi-decadal to centennial scales, temperature variability shows distinctly different regional patterns, with more similarity within each hemisphere than between them There were no globally synchronous multi-decadal warm or cold intervals that define a worldwide Medieval Warm Period or Little Ice Age, but all reconstructions show generally cold conditions between ad 1580 and 1880, punctuated in some regions by warm decades during the eighteenth century The transition to these colder conditions occurred earlier in the Arctic, Europe and Asia than in North America or the Southern Hemisphere regions Recent warming reversed the long-term cooling; during the period ad 1971–2000, the area-weighted average reconstructed temperature was higher than any other time in nearly 1,400 years

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Continental-scale temperature variability during the past two millennia

Volcanic eruptions contribute to climate variability, but quantifying these contributions has been limited by inconsistencies in the timing of atmospheric volcanic aerosol loading determined from ice cores and subsequent cooling from climate proxies such as tree rings. Here we resolve these inconsistencies and show that large eruptions in the tropics and high latitudes were primary drivers of interannual-to-decadal temperature variability in the Northern Hemisphere during the past 2,500 years. Our results are based on new records of atmospheric aerosol loading developed from high-resolution, multi-parameter measurements from an array of Greenland and Antarctic ice cores as well as distinctive age markers to constrain chronologies. Overall, cooling was proportional to the magnitude of volcanic forcing and persisted for up to ten years after some of the largest eruptive episodes. Our revised timescale more firmly implicates volcanic eruptions as catalysts in the major sixth-century pandemics, famines, and socioeconomic disruptions in Eurasia and Mesoamerica while allowing multi-millennium quantification of climate response to volcanic forcing.

/pdf/timing-and-climate-forcing-of-volcanic-eruptions-for-the-sw6kak6482.pdf

Timing and climate forcing of volcanic eruptions for the past 2,500 years

Changes in monsoon rainfall are caused by human-produced aerosols slowing the tropical atmospheric circulation. Observations show that South Asia underwent a widespread summertime drying during the second half of the 20th century, but it is unclear whether this trend was due to natural variations or human activities. We used a series of climate model experiments to investigate the South Asian monsoon response to natural and anthropogenic forcings. We find that the observed precipitation decrease can be attributed mainly to human-influenced aerosol emissions. The drying is a robust outcome of a slowdown of the tropical meridional overturning circulation, which compensates for the aerosol-induced energy imbalance between the Northern and Southern Hemispheres. These results provide compelling evidence of the prominent role of aerosols in shaping regional climate change over South Asia.

Anthropogenic aerosols and the weakening of the South Asian summer monsoon

[1] Previous studies have used small numbers of ice core records of past volcanism to represent hemispheric or global radiative forcing from volcanic stratospheric aerosols. With the largest-ever assembly of volcanic ice core records and state-of-the-art climate model simulations of volcanic deposition, we now have a unique opportunity to investigate the effects of spatial variations on sulfate deposition and on estimates of atmospheric loading. We have combined 44 ice core records, 25 from the Arctic and 19 from Antarctica, and Goddard Institute for Space Studies ModelE simulations to study the spatial distribution of volcanic sulfate aerosols in the polar ice sheets. We extracted volcanic deposition signals by applying a high-pass loess filter to the time series and examining peaks that exceed twice the 31-year running median absolute deviation. Our results suggest that the distribution of volcanic sulfate aerosol follows the general precipitation pattern in both regions, indicating the important role precipitation has played in affecting the deposition pattern of volcanic aerosols. We found a similar distribution pattern for sulfate aerosols from the 1783–1784 Laki and 1815 Tambora eruptions, as well as for the total b activity after the 1952–1954 low-latitude Northern Hemisphere and 1961–1962 high-latitude Northern Hemisphere atmospheric nuclear weapon tests. This confirms the previous assumption that the transport and deposition of nuclear bomb test debris resemble those of volcanic aerosols. We compare three techniques for estimating stratospheric aerosol loading from ice core data: radioactive deposition from nuclear bomb tests, Pinatubo sulfate deposition in eight Antarctic ice cores, and climate model simulations of volcanic sulfate transport and deposition following the 1783 Laki, 1815 Tambora, 1912 Katmai, and 1991 Pinatubo eruptions. By applying the above calibration factors to the 44 ice core records, we have estimated the stratospheric sulfate aerosol loadings for the largest volcanic eruptions during the last millennium. These loadings agree fairly well with estimates based on radiation, petrology, and model simulations. We also estimate the relative magnitude of sulfate deposition compared with the mean for Greenland and Antarctica for each ice core record, which provides a guideline to evaluate the stratospheric volcanic sulfate aerosol loading calculated from a single or a few ice core records.

/pdf/atmospheric-volcanic-loading-derived-from-bipolar-ice-cores-2bwa86f3ox.pdf

Atmospheric volcanic loading derived from bipolar ice cores: Accounting for the spatial distribution of volcanic deposition

Decoupling of provincial energy-related CO2 emissions from economic growth in China and its convergence from 1995 to 2017

Driving forces in energy-related carbon dioxide emissions in east and south coastal China: commonality and variations

[1] Understanding natural causes of climate change is vital to evaluate the relative impacts of human pollution and land surface modification on climate. We have investigated one of the most important natural causes of climate change, volcanic eruptions, by using 54 ice core records from both the Arctic and Antarctica. Our recently collected suite of ice core data, more than double the number of cores ever used before, reduces errors inherent in reconstructions based on a single or small number of cores, which enables us to obtain much higher accuracy in both detection of events and quantification of the radiative effects. We extracted volcanic deposition signals from each ice core record by applying a high-pass loess filter to the time series and examining peaks that exceed twice the 31-year running median absolute deviation. We then studied the spatial pattern of volcanic sulfate deposition on Greenland and Antarctica and combined this knowledge with a new understanding of stratospheric transport of volcanic aerosols to produce a forcing data set as a function of month, latitude, and altitude for the past 1500 years. We estimated the uncertainties associated with the choice of volcanic signal extraction criteria, ice core sulfate deposition to stratospheric loading calibration factor, and the season for the eruptions without a recorded month. We forced an energy balance climate model with this new volcanic forcing data set, together with solar and anthropogenic forcing, to simulate the large-scale temperature response. The results agree well with instrumental observations for the past 150 years and with proxy records for the entire period. Through better characterization of the natural causes of climate change, this new data set will lead to improved prediction of anthropogenic impacts on climate. The new data set of stratospheric sulfate injections from volcanic eruptions for the past 1500 years, as a function of latitude, altitude, and month, is available for download in a format suitable for forcing general circulation models of the climate system.

Volcanic Forcing of Climate over the Past 1500 Years: An Improved Ice-Core-Based Index for Climate Models

[1] In the paper ‘‘Volcanic forcing of climate over the past 1500 years: An improved ice core–based index for climate models’’ by C. Gao et al. (Journal of Geophysical Research, 113, D23111, doi:10.1029/2008JD010239, 2008) an erroneous unit of measure was given in the second sentence of paragraph [17]. The text should be ‘‘. . .by first dividing the loading by 1.5 10 g. . ..’’ We thank Youbing Peng for pointing out this typo. JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 114, D09103, doi:10.1029/2009JD012133, 2009 Click Here for Full Article

http://climate.envsci.rutgers.edu/pdf/GaoCorrection2009JD012133.pdf

Chaochao Gao

Papers

Atmospheric volcanic loading derived from bipolar ice cores: Accounting for the spatial distribution of volcanic deposition

Decoupling of provincial energy-related CO2 emissions from economic growth in China and its convergence from 1995 to 2017

Driving forces in energy-related carbon dioxide emissions in east and south coastal China: commonality and variations

Volcanic Forcing of Climate over the Past 1500 Years: An Improved Ice-Core-Based Index for Climate Models

Correction to “Volcanic forcing of climate over the past 1500 years: An improved ice core–based index for climate models”