Review & InterpretationAgronomy Journal • Volume 103, Issue 2 • 2011 351Climate Impacts on Agriculture: Implications for Crop ProductionJ. L. Hatfi eld,* K. J. Boote, B. A. Kimball, L. H. Ziska, R. C. Izaurralde, D. Ort, A. M. Thomson, and D. WolfePublished in Agron. J. 103:351–370 (2011)Published online 30 Dec 2010doi:10.2134/agronj2010.0303Copyright © 2011 by the American Society of Agronomy, 5585 Guilford Road, Madison, WI 53711. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher.There is mounting evidence the current changes in climate across the Northern Hemisphere will continue into the future and aff ect temperature, precipitation, and atmospheric CO2 concentration. Karl et al. (2009) presented an analysis of the recent changes in the climate of the United States and projected changes over the next century. Temperature and precipitation pat-terns across the United States for the next 30 yr show a warming trend of 1.5 to 2ºC and a slight increase in precipitation over most of the country (e.g., Tebaldi et al., 2006; Karl et al., 2009). Th ey projected an increase in the number of days when the temperature will be higher than the climatic normals by 5ºC (heat-waves), which will impact agricultural systems. Th ese authors also project an increase in warm nights, defi ned as occurring when the mini-mum temperature is above the 90th percentile of the climato-logical distribution for the day (Tebaldi et al., 2006; Karl et al., 2009). Coupled with these changes is the decrease in a number of frost days by 10% in the eastern half of the United States and an increase in the length of the growing season by more than 10 d. Karl et al. (2009) showed that precipitation events would change in frequency and intensity with a projected increase in spring precipitation, particularly in the Northeast and Midwest United States, and a decline in the southwestern United States. Th e increase in extreme temperature events, warm nights, and more variable precipitation will impact agriculture and agricul-tural production. A trend for warmer winters will aff ect perennial crops and weeds, and also expand the potential habitable range of some insect and disease pests. Although there is uncertainty about the absolute magnitude of the changes over the next 50yr, there is general agreement that CO2 levels will increase to near 450 μmol mol–1 (ppm), temperatures will increase by 0.8 to 1.0ºC, and precipitation will become more variable as defi ned in the IPCC AR4 analysis (IPCC, 2007). Changes in temperature have already caused longer growing seasons and begun to impact phenological phases (Schwartz et al., 2006; Wolfe et al., 2005, Xiao et al., 2008; Karl et al., 2009).An example of the potential of climate change impacts on agriculture is illustrated in a recent study by Ortiz et al. (2008) in which they assessed the potential impact on India wheat (Triticum aestivum L.) production if air temperature increased 0.8ºC over the next 50 yr. Th eir analysis showed that as much as 51% of the area in India currently classifi ed as high potential, irrigated, low rainfall mega-environment would be reclassifi ed to a heat-stressed, irrigated, short-season production mega-envi-ronment. Th is area currently accounts for 15% of the world’s wheat production and would undergo signifi cant reduction in yield unless cultivars and management practices adapted to the projected climate regime (e.g., higher levels of heat and water ABSTRACTChanges in temperature, CO2, and precipitation under the scenarios of climate change for the next 30 yr present a challenge to crop production. Th is review focuses on the impact of temperature, CO2, and ozone on agronomic crops and the implications for crop production. Understanding these implications for agricultural crops is critical for developing cropping systems resilient to stresses induced by climate change. Th ere is variation among crops in their response to CO2, temperature, and precipitation changes and, with the regional diff erences in predicted climate, a situation is created in which the responses will be further compli-cated. For example, the temperature eff ects on soybean [Glycine max (L.) Merr.] could potentially cause yield reductions of 2.4% in the South but an increase of 1.7% in the Midwest. Th e frequency of years when temperatures exceed thresholds for damage during critical growth stages is likely to increase for some crops and regions. Th e increase in CO2 contributes signifi cantly to enhanced plant growth and improved water use effi ciency (WUE); however, there may be a downscaling of these positive impacts due to higher temperatures plants will experience during their growth cycle. A challenge is to understand the interactions of the chang-ing climatic parameters because of the interactions among temperature, CO2, and precipitation on plant growth and development and also on the biotic stresses of weeds, insects, and diseases. Agronomists will have to consider the variations in temperature and precipitation as part of the production system if they are to ensure the food security required by an ever increasing population.J.L. Hatfi eld, Laboratory Director, National Laboratory for Agriculture and the Environment, Ames, IA 50011; K.J. Boote, Agronomy Dep., Univ. of Florida, Gainesville, FL 32611; B.A. Kimball, USDA-ARS, U.S. Arid-Land Agricultural Research Center, Maricopa, AZ 85138; L.H. Ziska, USDA Crop Systems and Global Change Lab., Beltsville, MD 20705; R.C. Izaurralde, Joint Global Change Research Institute, Pacifi c Northwest National Lab., Univ. of Maryland, College Park, MD 20740; D.R. Ort, USDA/ARS, Photosynthesis Research Unit, Univ. of Illinois, Urbana, IL 61801; A. M. Th omson, Joint Global Change Research Institute, Pacifi c Northwest National Lab., Univ. of Maryland, College Park, MD 20740; David W. Wolfe, Dep. of Horticulture, Cornell Univ., Ithaca, NY 14853. Received 9July 2010. *Corresponding author (jerry.hatfi [email protected]).Abbreviations: ET, evapotranspiration ; FACE, free-air carbon dioxide enrichment; HI, harvest index; LAI, leaf area index; VPD, vapor pressure defi cit; WUE, water use effi ciency.352 Agronomy Journal • Volume 103, Issue 2 • 2011stress) were