What was done
The authors evaluated several climatic trends and their impacts on agriculture in Bulgaria during the 20th century.  Then, using model output from several GCM simulations, they estimated the potential impact of predicted climate change on maize and wheat production in Bulgaria in the 21st century.

What was learned
Real-world data indicated there was "no significant change in the mean annual air temperature in Bulgaria during the 20th century."  Mean annual precipitation was found to have decreased slightly over that period, however, and several drought episodes, most notably in the 1940s and 1980s, were noted in the record.

Future climate, as simulated by several GCMs, predicted higher temperatures and a precipitation deficit in the 21st century.  Under such conditions and without accounting for the growth-enhancing benefits of atmospheric CO2 enrichment, maize and winter wheat yields in Bulgaria were predicted to decrease.  However, when the growth-enhancing effects of atmospheric CO2 enrichment were included in the model, "all GCM scenarios resulted in an increase in winter wheat yield."

What it means
First of all, it is apparent from the instrumental temperature record that it has not warmed in Bulgaria over the course of the past century.  Second, it is predicted that a doubling of the atmospheric CO2 concentration will enhance wheat yield between 12 and 49% in spite of a predicted 2.9 to 4.1°C increase in air temperature.  The authors predicted no increase in maize yield, however, as they thought atmospheric CO2 enrichment does not stimulate the growth of C4 crops; but this assumption is a misconception, as may be readily appreciated from a perusal of the numerous journal reviews of this topic that are listed in our Subject Index under the heading C4 Plants.  Hence, it is likely that all crops will likely experience increased yields in Bulgaria as the air's CO2 content continues to rise, irrespective of what the climate may do.