Summary for policymakers Technical summary 1. The climate system - an overview 2. Observed climate variability and change 3. The carbon cycle and atmospheric CO2 4. Atmospheric chemistry and greenhouse gases 5. Aerosols, their direct and indirect effects 6. Radiative forcing of climate change 7. Physical climate processes and feedbacks 8. Model evaluation 9. Projections of future climate change 10. Regional climate simulation - evaluation and projections 11. Changes in sea level 12. Detection of climate change and attribution of causes 13. Climate scenario development 14. Advancing our understanding Glossary Index Appendix.

Climate change 2001: the scientific basis

Changes in Atmospheric Constituents and in Radiative Forcing

Black carbon aerosol plays a unique and important role in Earth's climate system. Black carbon is a type of carbonaceous material with a unique combination of physical properties. This assessment provides an evaluation of black-carbon climate forcing that is comprehensive in its inclusion of all known and relevant processes and that is quantitative in providing best estimates and uncertainties of the main forcing terms: direct solar absorption; influence on liquid, mixed phase, and ice clouds; and deposition on snow and ice. These effects are calculated with climate models, but when possible, they are evaluated with both microphysical measurements and field observations. Predominant sources are combustion related, namely, fossil fuels for transportation, solid fuels for industrial and residential uses, and open burning of biomass. Total global emissions of black carbon using bottom-up inventory methods are 7500 Gg yr−1 in the year 2000 with an uncertainty range of 2000 to 29000. However, global atmospheric absorption attributable to black carbon is too low in many models and should be increased by a factor of almost 3. After this scaling, the best estimate for the industrial-era (1750 to 2005) direct radiative forcing of atmospheric black carbon is +0.71 W m−2 with 90% uncertainty bounds of (+0.08, +1.27) W m−2. Total direct forcing by all black carbon sources, without subtracting the preindustrial background, is estimated as +0.88 (+0.17, +1.48) W m−2. Direct radiative forcing alone does not capture important rapid adjustment mechanisms. A framework is described and used for quantifying climate forcings, including rapid adjustments. The best estimate of industrial-era climate forcing of black carbon through all forcing mechanisms, including clouds and cryosphere forcing, is +1.1 W m−2 with 90% uncertainty bounds of +0.17 to +2.1 W m−2. Thus, there is a very high probability that black carbon emissions, independent of co-emitted species, have a positive forcing and warm the climate. We estimate that black carbon, with a total climate forcing of +1.1 W m−2, is the second most important human emission in terms of its climate forcing in the present-day atmosphere; only carbon dioxide is estimated to have a greater forcing. Sources that emit black carbon also emit other short-lived species that may either cool or warm climate. Climate forcings from co-emitted species are estimated and used in the framework described herein. When the principal effects of short-lived co-emissions, including cooling agents such as sulfur dioxide, are included in net forcing, energy-related sources (fossil fuel and biofuel) have an industrial-era climate forcing of +0.22 (−0.50 to +1.08) W m−2 during the first year after emission. For a few of these sources, such as diesel engines and possibly residential biofuels, warming is strong enough that eliminating all short-lived emissions from these sources would reduce net climate forcing (i.e., produce cooling). When open burning emissions, which emit high levels of organic matter, are included in the total, the best estimate of net industrial-era climate forcing by all short-lived species from black-carbon-rich sources becomes slightly negative (−0.06 W m−2 with 90% uncertainty bounds of −1.45 to +1.29 W m−2). The uncertainties in net climate forcing from black-carbon-rich sources are substantial, largely due to lack of knowledge about cloud interactions with both black carbon and co-emitted organic carbon. In prioritizing potential black-carbon mitigation actions, non-science factors, such as technical feasibility, costs, policy design, and implementation feasibility play important roles. The major sources of black carbon are presently in different stages with regard to the feasibility for near-term mitigation. This assessment, by evaluating the large number and complexity of the associated physical and radiative processes in black-carbon climate forcing, sets a baseline from which to improve future climate forcing estimates.

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Bounding the role of black carbon in the climate system: A scientific assessment

Cause, conseguenze e strategie di mitigazione Proponiamo il primo di una serie di articoli in cui affronteremo l’attuale problema dei mutamenti climatici. Presentiamo il documento redatto, votato e pubblicato dall’Ipcc - Comitato intergovernativo sui cambiamenti climatici - che illustra la sintesi delle ricerche svolte su questo tema rilevante.

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Climate Change 2007: The Physical Science Basis.

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

Plume chemistry studies at a northern alberta power plant

[1] The Canadian Aerosol Module coupled with the Canadian third generation Global Climate Model was used to simulate the global distributions of size-segregated sea salt and sulphate aerosols of both anthropogenic and natural origins in the atmosphere. A sectional model of 12 size bins was used to treat the size distribution of sea salt and sulphate, which is assumed to be internally mixed in each size bin. The spatial and temporal distributions predicted by the model compare reasonably well with observations. The mixed aerosol simulations yield number and volume size distributions in the marine boundary layer (MBL) comparable with observations. Sea salt particles redistribute the mass and number distributions of sulphate aerosols by serving as a quenching agent to nucleation and as an additional surface area for condensation and by changing the cloud properties in the MBL. By differential simulations of global sea salt and sulphate it is found that the presence of sea salt increases the mass mean diameter of sulphate aerosols by up to a factor of 2 over the MBL with high sea salt concentrations and reduces the global sulphate aerosol mass in the surface MBL layer from 5 to 75% depending on the sea salt distributions. The high impacts are in the midlatitudes of both Northern and Southern Hemispheres with a minimum in the equatorial regions. In the polluted anthropogenic regions of North Pacific and Atlantic, sea salt reduces the sulphate concentration from 10 to 30%. The peak reductions of 50–75% occur in the roaring 40s of the Southern Hemisphere in spring and fall. The impact of sea salt on the annual global mass and number loading is estimated to be 9.13 and 0.76%, respectively. A reduction of 20–60% in the marine cloud droplet number concentrations (CDNC) was predicted because of the presence of sea salt, with greatest reductions in the roaring 40s south (40–70%) and in the midlatitude north (20–40%) where the sea salt concentrations were high. Along the equatorial regions some enhancement of total CDNC was simulated because of the presence of sea salt aerosols.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2002JD003181

Simulating the impact of sea salt on global nss sulphate aerosols

A study of sulphur dioxide deposition velocities to snow in northern Canada

Four years of precipitation chemistry data for eastern North America were used to investigate seasonal and geographical variations in SO 4 = /NO 3 - ratio. Several distinct regimes occur. One, in the region of heaviest acidic deposition extending from the states south of the Great Lakes across New England and southeastern Canada, has a very strong seasonal variation in the SO 4 = /NO 3 - molar ratio in deposition. The ratio ranges from about 1.5 in summer to about 0.5 in winter. Another, in the smaller area of Texas and surrounding states, shows the reverse seasonal pattern. Yet another, in the high plains states, has a double maximum in the ratio in Spring and Fall. The remainder of the region has an irregular seasonal pattern. Insight into the cause of SO 4 = /NO 3 - variations was obtained using a simple chemical transport box model. It showed that the chemical transformation of SO2 and NOX in the atmosphere is a major factor. A comparison of model predictions and observations indicate that in the vicinity of mid-western American sources the molar ratio of amount of SO2 oxidized in-cloud to that of NO2 is 0.5 in winter and 1.5 in summer.

The Spatial and Temporal Variation of the Sulphate to Nitrate Ratio in Precipitation in Eastern North America

A technique has been developed to enable measurement of photolyzable chlorine and bromine at trace levels in the troposphere. In this method, ambient air is drawn through a cylindrical flow cell, which is irradiated with a Xe arc lamp. In the reaction vessel of the photoactive halogen detector (PHD), photolytically active molecules Clp (including Cl2, HOCl, ClNO, ClNO2, and ClONO2) and Brp (including Br2, HOBr, BrNO, BrNO2, and BrONO2) are photolyzed, and the halogen atoms produced react with propene to form stable halogenated products. These products are then sampled and subsequently separated and detected by gas chromatography. The system is calibrated using low concentration mixtures of Cl2 and Br2 in air from commercially available permeation sources. We obtained detection limits of 4 pptv and 9 pptv as Br2 and Cl2, respectively, for 36 L samples.

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Leonard A. Barrie

Papers

Plume chemistry studies at a northern alberta power plant

Simulating the impact of sea salt on global nss sulphate aerosols

A study of sulphur dioxide deposition velocities to snow in northern Canada

The Spatial and Temporal Variation of the Sulphate to Nitrate Ratio in Precipitation in Eastern North America

Measurement Technique for the Determination of Photolyzable Chlorine and Bromine in the Atmosphere