Showing papers by "Andrew A. Lacis published in 1997"
Goddard Institute for Space Studies1, City University of New York2, University of Miami3, Columbia University4, Bronx High School of Science5, Massachusetts Institute of Technology6, National Oceanic and Atmospheric Administration7, Goddard Space Flight Center8, Langley Research Center9, United States Naval Research Laboratory10, Harvard University11, Hampton University12, Ames Research Center13, New York University14
TL;DR: This paper investigated the roles of climate forcings and chaos (unforced variability) in climate change via ensembles of climate simulations in which they add forcings one by one, concluding that most interannual climate variability in the period 1979-1996 at middle and high latitudes is chaotic.
Abstract: We investigate the roles of climate forcings and chaos (unforced variability) in climate change via ensembles of climate simulations in which we add forcings one by one. The experiments suggest that most interannual climate variability in the period 1979–1996 at middle and high latitudes is chaotic. But observed SST anomalies, which themselves are partly forced and partly chaotic, account for much of the climate variability at low latitudes and a small portion of the variability at high latitudes. Both a natural radiative forcing (volcanic aerosols) and an anthropogenic forcing (ozone depletion) leave clear signatures in the simulated climate change that are identified in observations. Pinatubo aerosols warm the stratosphere and cool the surface globally, causing a tendency for regional surface cooling. Ozone depletion cools the lower stratosphere, troposphere and surface, steepening the temperature lapse rate in the troposphere. Solar irradiance effects are small, but our model is inadequate to fully explore this forcing. Well-mixed anthropogenic greenhouse gases cause a large surface wanning that, over the 17 years, approximately offsets cooling by the other three mechanisms. Thus the net calculated effect of all measured radiative forcings is approximately zero surface temperature trend and zero heat storage in the ocean for the period 1979–1996. Finally, in addition to the four measured radiative forcings, we add an initial (1979) disequilibrium forcing of +0.65 W/m2. This forcing yields a global surface warming of about 0.2°C over 1979–1996, close to observations, and measurable heat storage in the ocean. We argue that the results represent evidence of a planetary radiative imbalance of at least 0.5° W/m2; this disequilibrium presumably represents unrealized wanning due to changes of atmospheric composition prior to 1979. One implication of the disequilibrium forcing is an expectation of new record global temperatures in the next few years. The best opportunity for observational confirmation of the disequilibrium is measurement of ocean temperatures adequate to define heat storage.
204 citations
TL;DR: The authors argue that aerosol effects on clouds have caused a large negative forcing, at least -1 Wm-2, which has substantially offset greenhouse warming, in the full period since the industrial revolution began, global warming is only half of that expected due to the principal forcing, increasing greenhouse gases.
Abstract: Observed climate change is consistent with radiative forcings on several time-scales for which the dominant forcings are known, ranging from the few years after a large volcanic eruption to glacial-to-interglacial changes. In the period with most detailed data, 1979 to the present, climate observations contain clear signatures of both natural and anthropogenic forcings. But in the full period since the industrial revolution began, global warming is only about half of that expected due to the principal forcing, increasing greenhouse gases. The direct radiative effect of anthropogenic aerosols contributes only little towards resolving this discrepancy. Unforced climate variability is an unlikely explanation. We argue on the basis of several lines of indirect evidence that aerosol effects on clouds have caused a large negative forcing, at least -1 Wm-2, which has substantially offset greenhouse warming. The tasks of observing this forcing and determining the microphysical mechanisms at its basis are exceptionally difficult, but they are essential for the prognosis of future climate change.
137 citations
03 Oct 1997
TL;DR: In this article, an iterative algorithm for retrieving a size distribution and size resolved refractive indices of aerosols from cloud free measurements of polarized sky radiances was developed, based on a parametric analysis of sky radiance and polarization measurements.
Abstract: A parametric analysis of sky radiance and polarization measurements based on a database of calculations indicated that there was information contained in the measurements that was not captured by the data base. We therefore developed an iterative algorithm for retrieving a size distribution and size resolved refractive indices of aerosols from cloud free measurements of polarized sky radiances. Preliminary results indicate that it is possible to retrieve a size resolved refractive index for a wide range of aerosol sizes, as well as an aerosol size distribution.
34 citations
TL;DR: In this paper, the authors obtain a highly efficient global climate model by defining a sector version (120° of longitude) of the coarse resolution Goddard Institute for Space Studies model II, which is chosen such that the amount of land as a function of latitude is the same as on Earth.
Abstract: We obtain a highly efficient global climate model by defining a sector version (120° of longitude) of the coarse resolution Goddard Institute for Space Studies model II. The geography of Wonderland is chosen such that the amount of land as a function of latitude is the same as on Earth. We show that the zonal mean climate of the Wonderland model is very similar to that of the parent model II.
16 citations