Background
Monoterpenes, which constitute a major fraction of volatile organic compounds given off by plants, have been described by Peñuelas and Llusia (2003) as helping to protect plants against high temperatures by acting as scavengers of reactive oxygen species produced within plants experiencing significant warming. In addition, they say that monoterpenes generate large quantities of organic aerosols that could affect climate by producing cloud condensation nuclei that lead to a net cooling of the earth's surface during the day via an enhanced reflection of incoming solar radiation.

What was done
In an experiment designed to see to what extent a doubling of the air's CO2 content and a 2-6°C increase in air temperature might impact the emission of monoterpenes from 20-year-old Scots pine (Pinus sylvestris L.) seedlings, Raisanen et al. (2008) studied the two phenomena (and their interaction) within closed-top chambers built on a naturally-seeded stand of the trees in eastern Finland that had been exposed to the four treatments -- ambient CO2 and ambient temperature, ambient temperature and elevated CO2, ambient CO2 and elevated temperature, elevated temperature and elevated CO2 -- for the prior five years.

What was learned
Over the five-month growing season of May-September, the three Finnish researchers found that total monoterpene emissions in the elevated-CO2-only treatment were 5% greater than those in the ambient CO2, ambient temperature treatment, and that emissions in the elevated-temperature-only treatment were 9% less than those in ambient air. In the presence of both elevated CO2 and elevated temperature, however, there was an increase of fully 126% in the total amount of monoterpenes emitted over the growing season.

What it means
On the basis of their dramatic combined (elevated CO2, elevated temperature) treatment results, Raisanen et al. conclude that "the amount of monoterpenes released by Scots pines into the atmosphere during a growing season will increase substantially in the predicted future climate." Hence, it can be appreciated that the positive impacts of this phenomenon, as described in the Background material for this review, should be equally dramatically increased, if both atmospheric CO2 concentration and air temperature rise as predicted by climate alarmists..

Reference
Peñuelas, J. and Llusia, J. 2003. BVOCs: plant defense against climate warming? Trends in Plant Science 8: 105-109.