|
Climate Monitoring and
Diagnostics Laboratory
Summary Report No. 25
TABLE
OF CONTENTS
|
Three-dimensional representation of the latitudinal distributions
of atmospheric carbon dioxide (top) and methane (bottom) in the marine
boundary layer during the period 1990-1999 based on measurements from
the NOAA CMDL cooperative air sampling network. Each surface represents
data smoothed in time and latitude and highlights significant features
of the atmospheric variation of each trace gas. Carbon Dioxide:
The global abundance of CO2 in the atmosphere (measured as moles CO2
per 106 moles air, "ppm") continues to increase at an average rate
of 1.5 ppm yr-1. Annual mean CO2 mixing ratios are 3-4 ppm higher
in the northern hemisphere where anthropogenic emissions are greatest.
Strong seasonality in the northern hemisphere is due to photosynthesis
and respiration of the terrestrial biosphere. Seasonality in the southern
hemisphere is much smaller and opposite in phase. Interannual variability
in the seasonal cycle is due to variation in the balance between photosynthesis
and respiration, and ocean uptake and release. Methane: The
global abundance of atmospheric CH4 (measured as moles CH4 per 109
moles air, "ppb") also continues to increase. Unlike CO2, the rate
of increase has been slowing. CH4 mixing ratios are ~150 ppb higher
in the northern hemisphere where anthropogenic and natural sources
of atmospheric methane are predominantly located. Seasonal patterns
in the northern hemisphere are caused by the interaction of seasonally
varying sources, sinks, and atmospheric transport. Seasonality in
the southern hemisphere is opposite in phase and driven mostly by
chemical destruction by OH radical. These smoothed surfaces are derived
from thousands of CO2 and CH4 observations and provide powerful constraints
on the global carbon cycle.
|
U.S. Department of Commerce
National Oceanic and Atmospheric Administration
Oceanic and Atmospheric Research
|
|