Transcript Aerosols
Anthropogenic Influences on Climate Snow/Ice Report Greenhouse Gases Aerosols Land Use and Land Cover Change For Next Class: Read pp. 3-23 of Snow Booklet Driving Question How do human activities affect global climate and how significant are those influences compared to natural causes of climate change? © AMS 2 Human Activity and Climate Change In 2013, the Intergovernmental Panel on Climate Change (IPCC) concluded that global warming since the mid-20th century very likely (estimated probability greater than 90%) was caused mostly (>50%) by human activities © AMS 3 Anthropogenic Forcings on Climate Greenhouse gases Aerosols Land use/land cover change Human Activity and Climate Change Trends in Greenhouse Gases “Most of the increase in globally-averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic GHG (greenhouse gas) concentrations.” (IPCC 2007) Fossil fuel combustion accounts for 75% of the increase in atmospheric carbon dioxide • deforestation is likely responsible for the balance © AMS Rising levels of other infrared-absorbing gases associated with human activity (e.g., methane, nitrous oxide, halocarbons, and ozone) enhance the greenhouse effect 5 Earth–Atmosphere Radiation Balance Figure 4.12 Atmospheric Absorption in the EM Spectrum Why are Greenhouse Gases Important? Absorb long-wave terrestrial radiation, heating the atmosphere, and radiating this energy back to the surface. Critical for life on Earth. Without greenhouse effect, surface temperatures would be extremely cold at night. Too much of a good thing, however, is a concern. A rectangular piece of coal in a wagon is on display in the middle of Pacific Avenue In Tacoma before the arrival of President Harrison in May, 1891. Life Magazine (1962) CO2 at Mauna Loa and South Pole (Red) and NOAA (Blue) IPCC AR5 CH4 at UCI (Green), AGAGE (Red) and NOAA (Blue) IPCC AR5 N2O at AGAGE (Red) and NOAA (Blue) IPCC AR5 What is Radiative Forcing? “The change in net (down minus up) irradiance (solar plus longwave; in W m-2) at the tropopause” (IPCC AR5 Ch. 2) Abbreviated RF Positive RF implies warming Negative RF implies cooling +3.0 w m-2 IPCC AR5 +3.0 w m-2 1000 Years of CO2 and Temperatures Figure 10.29 CO2 and Temperature Does correlation equate to causation? Why or why not? No denying that the anthropogenic greenhouse effect is playing a role: Question is how much? Atmospheric Aerosols Aerosols: solid or liquid particles suspended in the air Naturally occurring aerosols: particles from trees, sea salt, dust, and volcanic dust Anthropogenic aerosols: particles from the burning of fossil fuels and biomass, smoke, and agricultural dust Aerosols can influence weather and climate by directly and indirectly affecting the amount of solar radiation reaching the earth’s surface, which can lead to warming and cooling in different regions of the world. Overall RF is negative, however. Aerosol Optical Depth (AOD): variable used by scientists to describe the amount of solar radiation scattered or absorbed by aerosols (Instrument: sun photometer) Human Activity and Climate Change Aerosols 90% of anthropogenic aerosols are byproducts of fossil fuel burning in the Northern Hemisphere • cause either cooling (sulfurous aerosols) or warming (black carbon) of the atmosphere © AMS Aerosols can alter the number, mean size, and size distribution of cloud droplets 24 Human Activity and Climate Change Aerosols © AMS The direct radiative forcing of aerosols is estimated to offset the CO2 warming by almost one-third. (IPCC 2007) 25 Global Aerosol Optical Depth Trends in Global Aerosol Optical Depth IPCC AR5 Direct and Indirect Effects of Aerosols Aerosols scatter and absorb incoming solar radiation and impact cloud microphysics Direct and Indirect Effects of Aerosols Small black dots = aerosol particles Larger open circles = cloud droplets Straight lines = incident and reflected solar radiation Fig. 2.10 IPCC AR4 The Cloud Albedo Effect results in Negative RF. -0.82 w m-2 IPCC AR5 Reciprocal Relationship Aerosols Climate Appalachian Atmospheric Interdisciplinary Research an air quality/climate research and public outreach facility for exploring air pollution formation and transport and the relationship of pollution to a changing climate and its effects on regional ecosystems Participants: Howie Neufeld – Biology Brett Taubman – Chemistry Barkley Sive – Chemistry Rahman Tashakkori – Computer Science Baker Perry – Geography Jim Sherman – Physics Ryan Emanuel – NC State Doug Miller – UNCA Collaborating member of the NOAA-ESRL Global Aerosol Network (http://www.esrl.noaa.gov/gmd/aero/net/app/) and the NASA AErosol RObotic NETwork (AERONET, http://aeronet.gsfc.nasa.gov/) Changes in Surface Albedo What is surface albedo and why is it important in the context of climate change? How have humans changed surface albedo? Changes in Surface Albedo Anthropogenic changes to the physical properties of the land surface can perturb the climate Directly exerting a radiative forcing Modifying other processes such as latent and sensible heat fluxes Large-scale character of vegetation can affect surface albedo Albedo of agricultural land can be very different from that of a natural landscape, especially forest Particular important when snow is present, as open land can be highly reflective with snow cover, while a forest is not Albedo Figure 4.5 Human Activity and Climate Change Changes in land use and land cover Human development has transformed an estimated one-third to one-half of Earth’s land surfaces • Changes can affect the vertical flux of heat and moisture influences where and when thunderstorms occur may modify atmospheric and oceanic circulation • At middle latitudes, clearing of forests for agriculture and reforestation of abandoned farm land has caused regional climate change © AMS 39 Changes in Land Cover Since 1750 Cropland area expanded from 1750 to 1950 across Europe, Gangetic Plain, and in North America Since that time, croplands have been abandoned in Europe, North America and China, with an increase in forested areas Deforestation is occurring quite rapidly in the tropics How does deforestation (conversion of forest to grass) affect albedo, the surface energy balance, and RF? Radiative Forcing of Land Cover Change Land cover change since 1850 has generally led to higher surface albedo and a slight negative radiative forcing Best estimate is -0.24 w m-2 However, spatial variability is quite high, with some areas showing no change in RF and other areas more negative than -5 w m-2 With tropical deforestation becoming more significant in recent decades, warming due to reduced evaporation may become more significant globally than increased albedo. Black Carbon on Snow Presence of soot particles in snow causes a decrease of albedo and can affect snowmelt Best estimate of RF is +0.10 w m-2 http://www.arcticpeoples.org/ -0.15 w m-2 IPCC AR5 Anthropogenic Forcings on Climate Greenhouse gases Aerosols Land use/land cover change No denying that the anthropogenic activity is playing a role: Question is how much?