Global estimate of aerosol direct radiative forcing from satellite measurements

Atmospheric aerosols cause scattering and absorption of incoming solar radiation. Additional anthropogenic aerosols released into the atmosphere thus exert a direct radiative forcing on the climate system. The degree of present-day aerosol forcing is estimated from global models that incorporate a representation of the aerosol cycles. Although the models are compared and validated against observations, these estimates remain uncertain. Previous satellite measurements of the direct effect of aerosols contained limited information about aerosol type, and were confined to oceans only. Here we use state-of-the-art satellite-based measurements of aerosols and surface wind speed to estimate the clear-sky direct radiative forcing for 2002, incorporating measurements over land and ocean. We use a Monte Carlo approach to account for uncertainties in aerosol measurements and in the algorithm used. Probability density functions obtained for the direct radiative forcing at the top of the atmosphere give a clear-sky, global, annual average of -1.9 W m(-2) with standard deviation, +/- 0.3 W m(-2). These results suggest that present-day direct radiative forcing is stronger than present model estimates, implying future atmospheric warming greater than is presently predicted, as aerosol emissions continue to decline.     

A region of the Drosophila genome necessary for CNS development.

Mutations in genes involved in essential aspects of central nervous system development in Drosophila melanogaster are expected to be lethal. Thus, when searching for neurogenic mutants attention should be focused on embryonic lethal point mutants, for many of these might affect neural development. However, this approach can be very time consuming, for the location of neurogenic genes is unknown. A more convenient approach, which allows a faster screening of the genome, is to use relatively small chromosome deletions to determine whether the lack of a definite part of the genome affects neurogenesis. Once any region producing an interesting neural phenotype is found, it can be further analysed by the use of smaller deletions or point lethal mutants mapping within it, until the gene(s) responsible can be more precisely localised. We report here on a region of the Drosophila genome which has been found necessary for normal neurogenesis.