The relationship between near-surface air temperature over land and the annual amplitude of the atmosphere's seasonal CO2 cycle

The seasonal growth and decay of Northern Hemispheric terrestrial vegetatio n creates a seasonal oscillation in the atmospheric CO2 concentration in th e Northern Hemisphere. Over the past several decades, the amplitude of this seasonal cycle has risen substantially. Many potential causes of this phen omenon have been suggested; but the one that seems currently to be of most concern is global warming. This study thus seeks to determine if the rise i n the near-surface air temperature of the past 35 years has been the major factor in driving the contemporaneous increase in the amplitude of the Nort hern Hemisphere's seasonal CO2 cycle. Annual CO2 amplitude data from ten No rthern Hemispheric stations of the NOAA/CMDL continuous monitoring network were regressed against mean near-surface air temperatures over land areas l ocated within each 5 degrees latitude band stretching from the equator to 8 5 degrees N. Temperature effects were non-existent when the CO2 amplitude a nd temperature data were contemporaneous, whereas they were maximal when th e CO2 amplitude data lagged the temperature data by 2 years, declining slow ly thereafter to become non-existent again between a lag time of 6-7 years. For the peak-impact 2-year lag situation, low-latitude temperatures were m uch more strongly correlated with the CO2 amplitude data than were mid- or high-latitude temperatures. The 2-year-lag results for Mauna Loa and Point Barrow indicate that Northern Hemispheric warming may have been responsible for about a fifth of the annual CO2 amplitude increase observed at Mauna L oa from 1960 to 1995 and approximately a tenth of the amplitude increase re corded at Point Barrow over this period. Consequently, the majority of the Northern Hemispheric CO2 amplitude increase appears to be due to the influe nce of some other factor or combination of factors, a number of which have been suggested in the literature. (C) 1999 Elsevier Science B.V. All rights reserved.