Legacy of the US Water Conservation Laboratory (USWCL): II. Microclimatic Manipulations Via Free-Air CO2 Enrichment (FACE) and Temperature-Free-Air Controlled Enhancement (T-FACE) Technologies.

Concerns about the effects of the increasing atmospheric CO₂ concentrations and concomitant global warming led USWCL scientists to collaborate with engineers from the Brookhaven National Laboratory to develop free-air CO₂ enrichment technology, whereby the CO₂ concentration above open field could be controlled at elevated levels. Along with other scientists from the USDA-ARS Western Cotton Research Laboratory, the University of Arizona, and several other institutions, the first FACE experiment with publishable results was conducted on cotton at Maricopa, AZ in 1989. Following its success, additional experiments were conducted at Maricopa on cotton, wheat, and sorghum during the 1990s, and many more have been conducted in recent years around the world, with one conclusion being that on average yields of C3 grain crops will increase about 19% with CO₂ enrichment to 550 ppmv. Following on other prior remote sensing work at the USWCL, canopy temperatures were found to increase about 0.7°C, and, using the residual energy balance method, evapotranspiration was found to decrease about 10% under FACE.

Additional research in the 2000s by USWCL scientists led to development of arrays of infrared heaters to simulate global warming of field-grown crops, i.e. T-FACE. More than 20 such T-FACE experiments have been conducted or are underway around the world under several different ecosystems. A major T-FACE and planting date experiment on wheat by USWCL scientists and a University of Arizona collaborator showed rapid decline of wheat yields at temperatures above optimum. This dataset was used in a major AgMIP (Agricultural Model Inter-Comparison and Improvement Project) study with 30 wheat growth models. Extrapolating the ensemble model results from that study suggests that wheat yields are already being slowed at a majority of wheat-growing regions and that future global wheat production will fall by 6% for each °C of further warming.