Background
The authors report that isoprene emissions from forests in the vicinity of NOX pollution sources such as cities can contribute considerably to tropospheric ozone (O3) formation, especially during hot summer weather; and because increasing warmth and atmospheric CO2 concentrations are known to enhance leaf growth and forest productivity, they note that many people believe O3 formation will be increased in a warmer and CO2-enriched world of the future, due to higher forest isoprene emission rates. However, they say that most such projections "do not include the possible CO2-inhibition of leaf isoprene metabolism," as described by a number of experimental studies we have reviewed on our website (see Isoprene in our Subject Index).

What was done
Arneth et al. used a mechanistic isoprene-dynamic vegetation model of European woody vegetation to "investigate the interactive effects of climate and CO2 concentration on forest productivity, species composition, and isoprene emissions for the periods 1981-2000 and 2081-2100," which included a parameterization of the now-well-established direct CO2-isoprene inhibition phenomenon.

What was learned
"Across the model domain," as the four Swedish researchers describe it, the CO2-isoprene inhibition effect "has the potential to offset the stimulation of [isoprene] emissions that could be expected from warmer temperatures and from the increased productivity and leaf area of emitting vegetation."

What it means
Because ozone "is toxic for humans, animals, and plants even at relatively low concentrations," according to Arneth et al., their findings should be reassuring to people living in Europe -- and elsewhere -- for it would appear that a CO2-enriched and warmer world will provide a doubly beneficial future for them, with greater forest productivity and less associated ozone pollution.