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Fuglestvedt, Jan; Berntsen, Terje; Godal, Odd; Sausen, Robert; Shine, Keith; Skodvin, Tora
doi: 10.1023/A:1023905326842pmid: N/A
In this paper, we review existing and alternative metrics of climate change, with particular emphasis on radiative forcing and global warming potentials (GWPs), in terms of their scientific performance. Radiative forcing is assessed in terms of questions such as the utility of the concept, uncertainties and sensitivity to key assumptions. The assessment of emission indices focuses on the climate and other resulting impacts (end points) against which emissions are weighted; the extent to which (and how) time dependence is included, with regard to both emission control and impact; how cost issues are dealt with; and the sensitivity of the metrics to various assumptions. It is concluded that the radiative forcing concept is a robust and useful metric of the potential climatic impact of various agents and that there are prospects for improvement by weighing different forcings according to their effectiveness. We also find that although the GWP concept is associated with serious shortcomings, it retains advantages over any of the proposed alternatives in terms of political feasibility. Alternative metrics, however, make a significant contribution to addressing important issues, and this contribution should be taken into account in the further development of refined metrics of climate change.
Camuffo, Dario; Sturaro, Giovanni
doi: 10.1023/A:1023902120717pmid: N/A
Relative sea level (RSL) rise is a crucial issue for the safeguard of Venice and its historical buildings. The phenomenon over the last three centuries has been investigated by using a proxy of mean sea level: the height of the algae front on palaces. This indicator was accurately drawn by Canaletto and his pupils in their `photographic' paintings made with an optical camera obscura. The positions of the fronts in the 18th century and the present were compared. The RSL rise is due to a combination of natural and anthropogenic factors, both local and global, which affected the land subsidence. An analysis was performed to establish the long-term trend and distinguish between natural and local man contributions. A prudent scenario for the future would suggest a rate between 1.9 ± 0.4 mm yr−1 and 2.3 ± 0.4 mm yr−1.
Giorgi, Filippo; Bi, Xungqiang; Qian, Yun
doi: 10.1023/A:1023946010350pmid: N/A
We intercompare a series of multi-year simulations with a coupled regionalchemistry-climate model for east Asia to assess the relative importance ofdirect and indirect (Type I) effects of anthropogenic sulfate on the climateof the region. Both direct and indirect aerosol effects induce a negativeradiative forcing that results in a cooling of the surface and in a decrease of precipitation. Under present day sulfur emissions,the direct aerosol effects prevail during the cold season, while the indirecteffects dominate in the warm season (when cloudiness is maximum over the region). When both the direct and indirect effects are included, the surface cooling varies in the range of –0.1 to over –1 K throughout the region and extended areas ofstatistically significant cooling are found in all seasons except winter.The indirect effects largely dominate in inhibiting precipitation, especiallyduring the summer. When doubling the sulfur emissions, the direct effects aresubstantially strengthened, while the indirect effects are only marginally affected. This indicates that the indirect effects over the region might be asymptotically approaching their maximum efficiency. Overall, the indirect effects appear necessary to explain theobserved temperature record over some regions of China, at least in the warm season.A number of uncertainties need to be addressed, such as due to Type IIindirect effects, modeling of the relationship between aerosol concentration and cloud optical properties, and contribution of aerosols other than anthropogenic sulfate.
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