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Can a reduction of solar irradiance counteract CO2-induced climate change? – Results from four Earth system models

Author(s): Schmidt H, Alterskjær K, Karam DB, Boucher O, Jones A, Kristjansson JE, Niemeier U, Schulz M, Aaheim A, Benduhn F, Lawrence MG, Timmreck C

Published: March, 2012

Publisher: Earth System Dynamics Discussions

DOI: 10.5194/esdd-3-31-2012

Tags: Stratospheric Aerosols, Cloud Brightening, Climate Modelling

URL: http://www.earth-syst-dynam-discuss.net/3/31/2012/esdd-3-31-2012.html

Abstract: In this study we compare the response of four state-of-the-art Earth system models to climate engineering under scenario G1 of the GeoMIP and IMPLICC model intercomparison projects. In G1, the radiative forcing from an instantaneous quadrupling of the CO2 concentration, starting from the preindustrial level, is balanced by a reduction of the solar constant. Model responses to the two counteracting forcings in G1 are compared to the preindustrial climate in terms of global means and regional patterns and their robustness. While the global mean surface air temperature in G1 remains almost unchanged, the meridional temperature gradient is reduced in all models compared to the control simulation. Another robust response is the global reduction of precipitation with strong effects in particular over North and South America and northern Eurasia. It is shown that this reduction is only partly compensated by a reduction in evaporation so that large continental regions are drier in the engineered climate. In comparison to the climate response to a quadrupling of CO2 alone the temperature responses are small in experiment G1. Precipitation responses are, however, of comparable magnitude but in many regions of opposite sign.


The Geoengineering Dilemma: To Speak or not to Speak

Author(s): Lawrence MG

Published: August, 2006

Publisher: Climatic Change

DOI: 10.1007/s10584-006-9131-5

Tags: Research, Ethics

URL: http://www.springerlink.com/content/7178380t8g2p70x3/

Abstract: An intriguing dichotomy has developed within the field of atmospheric and climate research. On the one side, it has become common practice to examine pessimistic future scenarios of anthropogenic pollutant emissions and their environmental impacts. Not surprisingly, compared to the alternative “best guess” or “maximum feasible reduction” emissions scenarios, the pessimistic scenario simulations tend to predict large changes in the climate system and air quality. These scenarios can certainly attract attention to the possibly disastrous consequences of a careless environmental stewardship. However, they can also backfire politically, being seen as “unrealistic scare tactics” or “Hollywood horrors” put forth by scientists with environmentalist agendas. Furthermore, each simulation can only show one potential outcome among many possible states for a strongly perturbed climate. The predicted extreme outcomes of pessimistic scenarios will tend to vary widely from model to model. Unless this is communicated effectively, it can lead to confusion among policy makers, and can reduce confidence in such predictive studies. Nevertheless, such pessimistic scenario calculations are not only allowed, but are strongly condoned, for instance by the IPCC (2001), which employs these types of pessimistic scenarios as a central part of its regular assessments. This is well justified, given the most important outcome of these scenario calculations: scientists learn, and they learn a lot about the behavior of the earth system. The key is ensuring that the results are reported to the public and policy-making sectors as clearly and responsibly as possible, which is part of the purpose of the intense IPCC review procedure.


Export of Air Pollution from Southern Asia and its Large-Scale Effects

Author(s): Lawrence MG

Published: January, 2004

Publisher: The Handbook of Environmental Chemistry

DOI: 10.1007/b94526

Tags: Air Pollution, Tropospheric Aerosols, Climate Modelling

URL: http://www.springerlink.com/content/m7ny5yk7lf1lmk06/

Abstract: Southern Asia is one of the most heavily populated regions of the world. In contrast to much of the rest of the world, biofuel and biomass burning account for a large fraction of the total energy production in southern Asia compared to fossil fuel burning. This results in air masses which are relatively rich in carbon-containing aerosols, carbon monoxide, and hydrocarbons. The export of these polluted air masses is characterized by two main seasonal circulation patterns: the summer and winter monsoon. During summer, the heavy rains in this region effectively remove soluble gases and aerosols. Less soluble species, on the other hand, are lifted to the upper troposphere in deep convective clouds, and are then transported rapidly away from the region by the strong upper tropospheric winds, particularly towards northern Africa and the Mediterranean in the tropical easterly jet. During winter, the near-surface flow is mostly northeasterly, and the regional pollution forms a thick haze layer in the lower troposphere which spreads out over thousands of km between southern Asia and the Intertropical Convergence Zone (ITCZ). This chapter reviews the many observational and modeling studies which have examined the southern Asian outflow and its large scale effects.


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