HR: 17:45h
AN: B24A-08 [Abstracts]
TI: The Role of the Nitrogen Cycle in the Climate System
AU: * Holland, E A
EM: eholland@ucar.edu
AF: TIIMES and ACD, NCAR
PO BOX 3000, Boulder, CO 80307-3000, United States
AB:
The Fourth Assessment Report of Intergovernmental Panel on Climate Change was released earlier this year
and has generated world-wide attention This was the first Working Group 1 report to take an explicit look at the
global nitrogen cycle and how changes in the N cycle have impacted the climate system. The Working Group 1
report states the following: "Global atmospheric concentrations of carbon dioxide, methane and nitrous oxide
have increased markedly as a result of human activities since 1750 and now far exceed pre-industrial values
determined from ice cores spanning many thousands of years. It is very likely that the increase in the combined
radiative forcing from carbon dioxide, methane and nitrous oxide has been at least six times faster between1960
to 1999 than over any 40 year period during the two 50 millennia prior to the year 1800. "
Changes to the cycling of reactive nitrogen, not the stable atmospheric N2, play an important role in the
climate system. The most obvious is the rise in the atmospheric abundance of nitrous oxide since 1750. Nitrous
oxide is an important atmospheric tracer that allows us to track global changes to the nitrogen cycle. Nitrogen
plays a role in many other aspects of the climate system that are not immediately obvious. Biologically available
nitrogen is required for carbon uptake which helps fuel both oceanic and terrestrial carbon uptake. Without the
nitrogen fueled carbon uptake, the air-borne fraction of the carbon dioxide released from fossil fuel combustion
will increase according to the first coupled climate, carbon and nitrogen simulations done with the NCAR
Community Climate System Model (CCSM). NOx (NO+NO2) is one of the necessary precursors for
ozone formation that has increased more than thirty eight percent since the pre-industrial era. Understanding the
role of sources other than fossil fuel emissions, including soil NOx emissions and lightning formation of
NOx are important to understanding ozone formation. Recent European Space Agency satellite
observations of NO2 from the GOME and SCHIAMACHY satellites and CCSM simulations underscore the
importance of soil emissions of NOx. Nitrogen availability can play an important role in soil methane
oxidation and consumption which helps regulate atmospheric methane concentrations. Nitrogen, as ammonia,
ammonium and nitrate are important in the formation of aerosols that reflect incoming solar radiation and provide
a net cooling to the Earth's surface. Reactive nitrogen, e.g. N2O, NOx, NOy and NHx plays a
key role in the regulating the abundance of four of the top five greenhouses gases.
DE: 0315 Biosphere/atmosphere interactions (0426, 1610)
DE: 0365 Troposphere: composition and chemistry
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0469 Nitrogen cycling
SC: Biogeosciences [B]
MN: 2007 Fall Meeting