Wood fireplaces may seem like a charming way to warm your house, but they might also have negative environmental effects. Scientists have recently been studying the smoke and other small particles ("aerosols") released into the atmosphere by human activities to determine their effects on climate. Depending on their properties and in what part of the atmosphere they are found, aerosols (dust, droplets, and other matter floating in the atmosphere) can reflect sunlight back into space and cause cooling in two ways. Directly, they reflect sunlight back into space, thus reducing the amount of energy reaching the surface. Indirectly, they act as condensation nuclei that form clouds. Large concentrations of small droplets make these clouds more reflective, and inhibit rainfall and prolong cloud lifetimes. The indirect effect--more clouds and increased cloud life-- appears to have a greater impact on global climate. Aerosols can also absorb sunlight and cause increased local heating, and can affect the way heat is radiated back into space by the Earth. This all carries implications for national and international policies on industrial emissions and on the burning of forests and grasslands.
First, though, we must measure the effects of aerosols. While we know many
details of how aerosols act, we know neither the extent of their influence
nor the relative contribution of manmade aerosols as compared to naturally
occurring aerosols. GHCC scientists are now using data from sensors aboard
existing weather satellites to develop computer tools to measure
atmospheric aerosols and their effects in many areas of the globe.
Already, we have observed decreased changes in day/night temperature differences, cooler temperatures in regions of large aerosol emissions, and a gap between global temperature changes and what computer models predict when aerosols are not included. Using the Advanced Very High Resolution Radiometer (AVHRR) aboard operational weather satellites, we are measuring populations of sulfate (SO3) particles. (Particles in this range also are excellent nuclei for cloud formation.) Studies of the satellite data show marked differences in clouds over land and ocean, and over the northern and southern hemispheres (larger amounts over more industrially developed lands). Cloud droplets formed over land are about 4 to 6 micrometers smaller than over water. Marine cloud droplets are about 2 microns smaller in the Northern Hemisphere than in the Southern Hemisphere. They have also seen significant variations in droplet size during times such as dry seasons, when forests and croplands burn. Knowing such variations in droplet size is important in understanding the potential effects on climate, since smaller droplets (with larger number concentrations) tend to make the clouds more reflective to sunlight.
Using the AVHRR, GHCC scientists monitored more than five million square
kilometers of the forest and cerrado (grassland) regions over South
America during the 1985, 1986, and 1995 biomass burning seasons. We also
developed a new fire and smoke detection scheme. Using measurements from
the Earth Radiation Budget Experiment satellite, we computed the direct
regional radiative forcing of biomass burning aerosols. We found that more
than 70 percent of the fires occur in the grass and shrub land and in
savanna/grass and seasonal woodlands, largely due to agricultural
practices. We also found that the regional instantaneous net radiative
impact of biomass burning is one of cooling. These results have important
applications for future instruments aboard the Earth Observing System
[EOS] program. Instruments on the EOS-AM platform (that will cross the
dayside equator at local morning) could provide reliable estimates of the
direct radiative forcing of aerosols on a global scale, thereby reducing
the uncertainties in current global aerosol radiative forcing values.
Information provided by: http://wwwghcc.msfc.nasa.gov