CE 401 Climate Change Science and Engineering aerosols, carbon cycle 27 January 2011

any questions from last time? orbital cycles, aerosols HW 4 is due today HW 5 is posted on the web – due Tuesday 2/1 HW 3 which was due Tuesday: - 1 w/m^2 in solar output  0.05°C change in equilibrium temperature - 31  30% change in albedo  0.9 °C change in equilibrium temperature - removing CO 2 from the radiance curve  ~ 8°C change in temperature - + 3% change in solar flux from Earth revolution about sun  ~4°C change

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aerosols and their effects on climate big driver – HUGE driver, both human induced and natural RF not well understood – hardly on the data sheets in 1990 not well measured – satellites and ground networks – short record of data parameters that affect aerosols and their RF not understood global effects not well understood – clouds (height and distribution)

increasing complexity of the modeling world

aerosols: solid particles or liquid particles suspended in the air size: few nanometers to microns in size: x variation in size have major impacts on climate physical properties: shape, size, chemical composition particles at the small end play a large role in cloud physics condensation nuclei for clouds EPA regulates particles in the US PM10 and PM2.5 – CEE 341, 415 key aerosol groups: sulfates organic carbon black carbon nitrates mineral dust sea salt aerosols of clump together to form complex mixtures 90% of aerosols (by mass) are natural in origin about 10% of global aerosols are generated by human activity problems in dealing with aerosol effect: diversity in size, composition and origin; spatial and temporal variability; source; injection height aerosols removed primarily through cloud processing and wet and dry deposition

aerosol RF effects are categorized into direct and indirect effects: direct: mechanism by which aerosols scatter and absorb radiation  change in the radiative balance of the Earth system organic carbon, sulphate, nitrate, black carbon, dust, biomass burning indirect: mechanism by which aerosols modify the microphysical and hence the radiative properties, amount, and lifetimes of clouds size, shape, chemical composition, etc.

volcanic pollensea saltsoot fossil fuel combustion  SO2 which reacts with H2O and gases to  sulfate aerosols biomass burning  organic carbon and black carbon transportation sector  prolific producer of aerosols aerosols are usually modeled as spherical in shape – do they look spherical?????? properties: shape, size, composition, chemistry, polarization, index of refraction, mass,

- aerosol optical depth is the fundamental measure of quantity and distribution of aerosols - absorbance is proportional to exp{-  } where  is the optical depth. AOD is a measure of incident light scattered or absorbed.   is prop to path length and extinction cross section average AOD

global aerosol distribution. Yellow = coarse particles like dust, red = fine particles like smoke or air pollution. How do you compute light attenuation at a location from this picture??? MODIS data

Figure 2.11 MODIS aerosol measurements. Top, circles are AERONET sites, bottom aerosol lidar network

MODIS 9 Oct 2010

volcanic aerosol effects on temperature (anomaly)

from Atmos Aerosol Properties and Climate Impacts, on class website now

primary effect of aerosols is a brightening of the planet when viewed from space primary indirect effect of aerosols on clouds is an increase in cloud brightness, change in precipitation and an increase in lifetime  increased earth albedo  less sunlight at surface in regions with high concentrations of anthropogenic aerosols, aerosol RF is much stronger than the magnitude of the GHG

average tropospheric aerosol lifetime at a week or less  can travel 1000’s of km

different aerosols scatter or absorb sunlight differently depending on physical prop black carbon effects - modeled

indirect effects of aerosols: cloud formation and cooling aerosols play a critical role in cloud formation natural aerosols are most important but human produced aerosols have a significant impact ship tracks – white clouds and map of cloud droplet size  where ship exhaust is mixed with cloud layer, droplets are smaller

modeling results from different groups: direct RF

measurements of aerosols from satellites and networks of instruments AERONET

NASA Global Hawk at Edwards AFB, CA you guys ought to get involved in atmospheric studies – it is one heck of a lot of fun!

outstanding issues in aerosol effects on climate change: composition optical absorption impacts on surface radiation and heating long term trends total RF

global carbon cycle

over millions of years, CO 2 is removed from the atmosphere through weathering of rocks and through burial in marine sediments of carbon fixed by marine plants burning fossil fuels returns carbon captured by plants in geologic history to the atmosphere current levels of CO 2 are nearly 50% higher than in the past 700k yrs during glacial periods, CO 2 removed from the atmosphere was stored in the oceans CO 2 prior to 1750 was about 280 ppm and had been stable for ~ 10k yrs since 1750 the amount of CO 2 in the atmosphere has increased ~ 40% from human activities fossil fuel combustion deforestation land use change biomass burning crop production conversion of grasslands to croplands

CO 2 and CH 4 play major roles in the natural cycle of carbon large flows of carbon among the ocean, terrestrial biosphere and atmosphere stable for past 10k yrs terrestrial plants capture CO 2 from the atmosphere photosynthesis plant, soil, and animal respiration  carbon to atmosphere CO 2 is continuously exchanged between atmosphere and ocean CO 2 entering ocean waters  bicarbonate (HCO 3 - ) and carbonate (CO 3 2- ) ions residence time of dissolved inorganic carbon in surface ~ 10 yrs intermediate depths circulate on decades to centuries time scale abyssal depths mix on millennial time scales what are the fluxes of carbon between the atmosphere, biosphere, hydrosphere

HW 2 – change in annual CO2 in the atmosphere

fraction of fossil fuel emissions remaining in the atmosphere airborne fraction of CO2 has remained constant at 0.55 since 1959  terrestrial biosphere and oceans together have removed 45% of fossil CO2 for 45 yrs

source: IPCC 2007 The Climate System - very complicated

compare these two figures  some idea of the errors involved in the fluxescompare these two figures  some idea of the errors involved in the fluxes