GeoLibrary » Reference Library

Search Results

Showing results 1 - 2 of 2

for: Caldeira K + Climate Dynamics

« New Search

Dependence of climate forcing and response on the altitude of black carbon aerosols

Author(s): Ban-Weiss GA, Cao L, Bala G, Caldeira K

Published: April, 2011

Publisher: Climate Dynamics

DOI: 10.1007/s00382-011-1052-y

Tags: Stratospheric Aerosols, Climate Modelling, Precipitation, Short-Lived Climate Forcers, Tropospheric Aerosols

URL: http://dge.stanford.edu/labs/caldeiralab/Caldeira_research/BanWeiss_Cao.html

Abstract: Black carbon aerosols absorb solar radiation and decrease planetary albedo, and thus can contribute to climate warming. In this paper, the dependence of equilibrium climate response on the altitude of black carbon is explored using an atmospheric general circulation model coupled to a mixed layer ocean model. The simulations model aerosol direct and semi-direct effects, but not indirect effects. Aerosol concentrations are prescribed and not interactive. It is shown that climate response of black carbon is highly dependent on the altitude of the aerosol. As the altitude of black carbon increases, surface temperatures decrease; black carbon near the surface causes surface warming, whereas black carbon near the tropopause and in the stratosphere causes surface cooling. This cooling occurs despite increasing planetary absorption of sunlight (i.e. decreasing planetary albedo). We find that the trend in surface air temperature response versus the altitude of black carbon is consistent with our calculations of radiative forcing after the troposphere, stratosphere, and land surface have undergone rapid adjustment, calculated as “regressed” radiative forcing. The variation in climate response from black carbon at different altitudes occurs largely from different fast climate responses; temperature dependent feedbacks are not statistically distinguishable. Impacts of black carbon at various altitudes on the hydrological cycle are also discussed; black carbon in the lowest atmospheric layer increases precipitation despite reductions in solar radiation reaching the surface, whereas black carbon at higher altitudes decreases precipitation.


Albedo enhancement of marine clouds to counteract global warming: Impacts on the hydrological cycle

Author(s): Bala G, Caldeira K, Nemani R, Cao L, Ban-Weiss GA, Shin HJ

Published: June, 2010

Publisher: Climate Dynamics

DOI: 10.1007/s00382-010-0868-1

Tags: Cloud Brightening, Environmental Side-Effects, Precipitation, Climate Modelling, Cloud Physics

URL: http://www.springerlink.com/content/9569172415150486/

Abstract: Recent studies have shown that changes in solar radiation affect the hydrological cycle more strongly than equivalent CO2 changes for the same change in global mean surface temperature. Thus, solar radiation management "geoengineering" proposals to completely offset global mean temperature increases by reducing the amount of absorbed sunlight might be expected to slow the global water cycle and reduce runoff over land. However, proposed countering of global warming by increasing the albedo of marine clouds would reduce surface solar radiation only over the oceans. Here, for an idealized scenario, we analyze the response of temperature and the hydrological cycle to increased reflection by clouds over the ocean using an atmospheric general circulation model coupled to a mixed layer ocean model. When cloud droplets are reduced in size over all oceans uniformly to offset the temperature increase from a doubling of atmospheric CO2, the global-mean precipitation and evaporation decreases by about 1.3% but runoff over land increases by 7.5% primarily due to increases over tropical land. In the model, more reflective marine clouds cool the atmospheric column over ocean. The result is a sinking motion over oceans and upward motion over land. We attribute the increased runoff over land to this increased upward motion over land when marine clouds are made more reflective. Our results suggest that, in contrast to other proposals to increase planetary albedo, offsetting mean global warming by reducing marine cloud droplet size does not necessarily lead to a drying, on average, of the continents. However, we note that the changes in precipitation, evaporation and P-E are dominated by small but significant areas, and given the highly idealized nature of this study, a more thorough and broader assessment would be required for proposals of altering marine cloud properties on a large scale.


Showing results 1 - 2 of 2

for: Caldeira K + Climate Dynamics

« New Search

Website by Pandemedia