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.

/pdf/bounding-the-role-of-black-carbon-in-the-climate-system-a-1fc3novd9r.pdf

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.

/pdf/climate-change-2007-the-physical-science-basis-1x93ttz9jt.pdf

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

Air Chemistry Observations in the Canadian Arctic

Strong winds cause lifting of large amounts of sand and dust from bare, dry soils into the atmosphere. For countries in and downwind of arid regions, airborne sand and dust presents serious risks to the environment, property and human health. Impacts on health include respiratory and cardio-vascular problems, eye infections and in some regions, diseases such as meningitis and valley fever. Dust can efficiently carry irritating spores, bacteria, viruses and persistent organic pollutants. It can also efficiently transport nutrients to parts of the world oceans and affect marine biomass production. Other impacts include negative effects on the ground transport, aviation, agriculture and visibility. The Inter-governmental Panel on Climate Change (IPCC) recognizes dust as a major component of the atmospheric aerosol that is an essential climate variable. Dust aerosol has important effects on weather through feedback on atmospheric dynamics, clouds and precipitation formation.

/pdf/wmo-sand-and-dust-storm-warning-advisory-and-assessment-2b039wdc0z.pdf

WMO Sand and Dust Storm Warning Advisory and Assessment System (SDS-WAS): Research Implementation Status

In the last fifteen years, considerable progress has been made in understanding the occurrence, origin, pathways, history and relevance to global change of natural and anthropogenic substances in the polar troposphere. In addition, glacial snow and ice have provided historical records of tropospheric composition of greenhouse gases and of snow deposited in the polar regions. One of the most remarkable features of polar studies is the extreme geographical contrast between the Arctic and Antarctic. The Arctic troposphere is underlain by an active ocean surrounded by pollutant-emitting, industrialized continents while the Antarctic troposphere lies over a massive, 4 km thick, ice sheet surrounded by the pollution-free southern ocean. The Arctic troposphere is much more polluted (Arctic haze) than its southern counterpart and has different exposure to compounds of natural origin such as wind blown dust or marine gases and particles. The pollution has an impact on both physical and chemical climatology. Anthropogenic Arctic haze aerosols of black carbon and sulphate have a net warming influence in the north in contrast to elsewhere on the globe where (with less black carbon) they tend to offset the impact of anthropogenic greenhouse gases. Biogeochemical cycles of many substances including carbon, sulfur and nitrogen are perturbed. Compounds potentially toxic to polar ecosystems also accumulate.

Polar Atmosphere and Snow Chemistry

The main part of this book has described in detail the important components of the atmospheric cycles of sulfur and nitrogen—emission, transformation, transport, and deposition. Towards the end of the Bermuda workshop, two brief sessions were convened to discuss specific aspects of the two atmospheric cycles. These discussions focussed on parts or combinations of parts of special concern to the participants. However, these discussions did not result in atmospheric budgets for sulfur and nitrogen not only because of a lack of time but also because of the large uncertainties in the deposition, especially in the emission estimates.

The Cycling of Sulfur and Nitrogen in the Remote Atmosphere

The story of the importance of atmospheric chemistry begins with the origin and evolution of life on Earth The accumulation of greenhouse gases in Earth’s atmosphere allowed surface temperatures to be maintained above the freezing point of water Reactions involving carbon, hydrogen, and nitrogen compounds in the primeval soup led to the formation of self-replicating molecules, and, about 500 million years ago, the rise of atmospheric oxygen led to the formation of the stratospheric ozone layer, which protects life on Earth from extremely harmful levels of solar ultraviolet radiation Running in the shadow of these major events has been a full suite of atmospheric chemistry processes affecting and being affected by the evolving nature of both terrestrial and oceanic life Some of these processes include biogeochemical cycling of elements, long-range transport of nutrients, regulation of temperature, and exposure to air pollution

Leonard A. Barrie

Papers

Air Chemistry Observations in the Canadian Arctic

WMO Sand and Dust Storm Warning Advisory and Assessment System (SDS-WAS): Research Implementation Status

Polar Atmosphere and Snow Chemistry

The Cycling of Sulfur and Nitrogen in the Remote Atmosphere

Changes in the Chemical Composition of the Atmosphere and Potential Impacts