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

The flux of anthropogenic sulphur into the arctic from mid-latitudes in 1979/80

Concentrations of methyl mercury (MeHg) and total mercury (THg) in precipitation were measured at the Experimental Lakes Area (ELA), a remote field station in northwestern Ontario. We found that precipitation was a source of both MeHg and THg to boreal ecosystems, but at lower rates than in industrialized regions of North America and Scandinavia. MeHg concentrations in precipitation ranged from 0.010 to 0.179 ng L1 and were highest when events originated west of the ELA. THg concentrations in precipitation ranged from 0.95 to 9.31 ng L1 and were highest when the events came from the southeast. There was no relationship between THg and MeHg over time in precipitation. Inputs of both MeHg and THg to ecosystems were highest during summer months.

Wet Deposition of Methyl Mercury in Northwestern Ontario Compared to Other Geographic Locations

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/94JD01929

Polar Sunrise Experiment 1992 (PSE 1992): Preface

Seasonal and geographic variations of methanesulfonic acid in the arctic troposphere

Simultaneous measurements of atmospheric and surface water dimethyl sulfide (DMS) concentrations were taken aboard the icebreaker USCGC Polar Sea from July to October 1994, as part of a joint Canada/United States circumnavigation of North America, an expedition with a unique Arctic Ocean transect. Atmospheric DMS concentrations around North America varied between 0.25 and 50 nmol m−3 (mean = 5.1 nmol m−3, σ = 8.5 nmol m−3, n = 89) with highest values occurring near (south of) the Arctic ice edge. Surface water DMS concentrations ranged between 0.1 and 12.6 nmol L−1 (mean = 2.2 nmol L−1, σ = 2.7 nmol L−1, n = 46) with highest values in the western Arctic Ocean and off the U.S. east coast, near the Sargasso sea. In the Arctic Ocean, maximum concentrations in air and water were found along the ice edge in the Chukchi Sea region. Atmospheric DMS decay rates of 68% per day and 38% per day were deduced from observations between 70° and 76°N (continental shelf and slope of Chukchi Sea) on the west side and between 80° and 90°N (central Arctic Ocean) for the east side of the Arctic Ocean, respectively. Ocean to atmosphere flux estimates of DMS were determined using the Liss-Merlivat empirical dependence of exchange coefficient on wind speed, DMS air concentrations, Henry's law constants, and DMS water concentrations. DMS fluxes varied between 0.0017 and 30 μmol m−2 d−1, respectively, with higher fluxes in regions with open water. The Arctic Ocean contributed 0.063 Tg S (DMS) (0.4% of DMS from the world oceans) during the summer of 1994. A simple one-dimensional (1-D) photochemical box model, applied to six case studies, showed that the atmospheric lifetime of DMS in the high Arctic was 2.5 to 8 days, whereas at 16°–33°N it was 1 to 2 days. Modeled DMS decay rates for these regions, using the 1-D model, accounted for only 33% of the measured decay rate. This result also suggests that halogen chemistry, reactions with Br/BrO, may be an important sink for DMS in the Arctic atmosphere.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/1999JD900207

Leonard A. Barrie

Papers

The flux of anthropogenic sulphur into the arctic from mid-latitudes in 1979/80

Wet Deposition of Methyl Mercury in Northwestern Ontario Compared to Other Geographic Locations

Polar Sunrise Experiment 1992 (PSE 1992): Preface

Seasonal and geographic variations of methanesulfonic acid in the arctic troposphere

Flux estimation of oceanic dimethyl sulfide around North America