That leads me to wonder if we could use cloud seeding to darken Greenland, or the Arctic sea ice.
A On Dec 3, 2012 9:42 PM, "Rau, Greg" <[email protected]> wrote: > Cryoscience: Snowfall brightens Antarctic future > **** > > - Charles S. > Zender<http://www.nature.com/nclimate/journal/v2/n11/full/nclimate1730.html#auth-1> > **** > > Nature Climate Change**** > > 2,**** > > 770–771**** > > (2012)**** > > doi:10.1038/nclimate1730**** > > Published online**** > > 26 October 2012 **** > > Snowpacks absorb more sunlight as they warm. The Antarctic Plateau may > buck this trend over the twenty-first century as increased snowfall there > inhibits the snowpack from dimming.**** > > The colour of snow tells a remarkable story. To the human eye, snow > appears white because its reflectance of visible light is uniformly high. > However, its reflectance changes with astonishing abruptness at other > wavelengths, and is a complex function of the exact ice crystal size and > shape1<http://www.nature.com/nclimate/journal/v2/n11/full/nclimate1730.html#ref1>, > 2<http://www.nature.com/nclimate/journal/v2/n11/full/nclimate1730.html#ref2>. > Pristine snow is a valuable shield against global warming as it reflects up > to 85% of sunlight and traps only the remainder as > heat1<http://www.nature.com/nclimate/journal/v2/n11/full/nclimate1730.html#ref1>, > 3<http://www.nature.com/nclimate/journal/v2/n11/full/nclimate1730.html#ref3>, > 4<http://www.nature.com/nclimate/journal/v2/n11/full/nclimate1730.html#ref4>. > This is why almost imperceptible reductions in snow reflectance owing to > warming and > pollution3<http://www.nature.com/nclimate/journal/v2/n11/full/nclimate1730.html#ref3>, > 5<http://www.nature.com/nclimate/journal/v2/n11/full/nclimate1730.html#ref5>have > become a great concern. Increased heat trapping by darker snow > triggers a vicious feedback cycle that speeds the greying of > snow5<http://www.nature.com/nclimate/journal/v2/n11/full/nclimate1730.html#ref5>, > 6<http://www.nature.com/nclimate/journal/v2/n11/full/nclimate1730.html#ref6>, > 7<http://www.nature.com/nclimate/journal/v2/n11/full/nclimate1730.html#ref7>. > With temperatures increasing globally, what, if anything, will oppose the > self-reinforced darkening of snow and keep it from melting even faster? > Writing in *Nature Climate Change*, Picard *et > al*.8<http://www.nature.com/nclimate/journal/v2/n11/full/nclimate1730.html#ref8>use > snow-colour measurements to deduce that fresh snowfall inhibits the > seasonal greying of snow on the Antarctic Plateau by up to 3%, and reduces > summertime temperatures there by up to 4 °C. On climate timescales, the > increase in Antarctic snowfall expected with twenty-first-century warming > may be enough to prevent the surface from further darkening.**** > > Antarctica's reprieve from darker snow is a welcome surprise, because the > enemies of snow reflectance are time and temperature, which is projected to > rise by about 3 °C this century. Much like ice cubes in a home freezer, > snow crystals lose their sharp facets to duller, rounder shapes as they age > 1<http://www.nature.com/nclimate/journal/v2/n11/full/nclimate1730.html#ref1>, > 9<http://www.nature.com/nclimate/journal/v2/n11/full/nclimate1730.html#ref9>(Fig. > 1<http://www.nature.com/nclimate/journal/v2/n11/full/nclimate1730.html#f1>). > Heat accelerates this metamorphism so that pristine, sharply faceted fresh > crystals quickly grow during summer to become larger, rounder, aged snow, > which absorbs more heat and reflects less > sunlight1<http://www.nature.com/nclimate/journal/v2/n11/full/nclimate1730.html#ref1>, > 5<http://www.nature.com/nclimate/journal/v2/n11/full/nclimate1730.html#ref5>, > 9<http://www.nature.com/nclimate/journal/v2/n11/full/nclimate1730.html#ref9>. > Snow reflectance also changes during wind events (which shatter and > sublimate crystals) and as a result of surface crusts and ripples. The > findings reported by Picard and colleagues suggest that these secondary > contributors explain less than one-third of changes in summer snow > reflectance on the Antarctic Plateau. Temperature and snowfall are the main > players.**** > > > The Antarctic Plateau endures long periods of polar night, during which > its visible reflectance cannot be measured, so Picard and colleagues > focused on the seasonal behaviour of a reflectance proxy — the snow grain > size. First they teased grain-size information from the > wavelength-dependent surface microwave emissions measured daily by > meteorological satellites. A sophisticated model of the microwave signal > travelling from the surface through the atmosphere best matches the > measured signal when the snowpack is modelled as smaller, younger surface > grains atop larger, inactive snow grains deposited in previous seasons.*** > * > > ** ** > > > -- > You received this message because you are subscribed to the Google Groups > "geoengineering" group. > To post to this group, send email to [email protected]. > To unsubscribe from this group, send email to > [email protected]. > For more options, visit this group at > http://groups.google.com/group/geoengineering?hl=en. > -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en.
