||Sage RF, Sage TL, Kocacinar F. Photorespiration and the evolution of C4 photosynthesis. Annu Rev Plant Biol. 2012 63: 19-47. doi: 10.1146/annurev-arplant-042811-105511. p.28 right column 2nd paragraphPubMed ID22404472
||Rowan F. Sage, The evolution of C4 photosynthesis, New Phytologist Volume 161, Issue 2, pages 341–370, February 2004 DOI: 10.1111/j.1469-8137.2004.00974.x
||p.28 right column 2nd paragraph:"Models of photorespiration illustrate the impact of CO2 variation, elevated temperature, and low humidity on the photorespiratory potential of C3 vegetation (Figure 4). At elevated CO2 (>1,000 ppm), photorespiration is minor at all temperatures. At chloroplast CO2 levels corresponding to current atmospheres, photorespiration exceeds 25% of the photosynthesis rate above 30°C–35°C, assuming stomatal conductance is regulated to give Ci/Ca (intercellular CO2 partial pressure to ambient CO2 partial pressure) values of 0.7–0.8, which are typical in nonstressed C3 vegetation (primary source)."