The impact of climate change on sugarbeet yield in the UK: 1976–2004 K.W. JAGGARD 1 *, A. QI 1 AND M.A. SEMENOV 2 1 Broom’s Barn Research, Higham, Bury St Edmunds, Suffolk IP28 6NP, UK 2 Biomathematics & Bioinformatics, Rothamsted Research, Harpenden, Herts AL5 2JQ, UK (Revised MS received 27 November 2006; First published online 28 February 2007) SUMMARY Since the 1970s, the delivered sugar yield per hectare has risen at an average annual rate of 0 . 111 t/ha, while the sugar yield in the official variety trials has increased at an average annual rate of 0 . 204 t/ha. These increases are usually considered to be the result of improvements in varieties and in beet agronomy. The present paper considers the possible impact of recent changes in climate on UK sugar yields by using the Broom’s Barn Crop Growth Model and daily weather data collected over the last 30 years. Simulations of sugar yield using weather in eastern England since 1976 increased by an average annual rate of 0 . 139 t/ha, which accounted for about two thirds of the rate in the official variety trials. This increase was not an artefact of the accuracy of weather recording but it was, in part, accounted for by the trend to earlier sowing. Although it was not statistically significant, the earlier sowing trend was associated with an increase of 0 . 025 t/ha per year and was an indirect effect of the climate change. The annual deviations from these trends have not tended to become signifi- cantly bigger or smaller over the three decades. The model is not variety-specific, so it makes no allowance for variety improvements during the last 30 years. Clearly, varieties have improved so the implication must be that some of the changes in agronomy have tended to decrease the yields sig- nificantly. The changes in agronomic practice most likely to be responsible are the extension of the crop processing campaign, leading to greater post-harvest storage losses, and a decrease in the irri- gated area. INTRODUCTION Sugar yields have risen by 0 . 11 t/ha per year in recent years in the UK (Bruhns et al. 2005). Similar increases over the last 30 years are being reported in France (0 . 17 t/ha per year ; ITB 2003) and in trials in Germany (0 . 14 t/ha per year; Ma¨rla¨ nder et al. 2003). It is usually assumed that these increases result from a combination of the use of improved varieties and improved agronomic practice (ITB 2003; Ma¨ rla¨ nder et al. 2003). These assumptions are justified only if changes in the weather, over a period of a few years, have had no impact on yield. However, our climate has been changing over recent decades probably in response to increasing atmospheric concentrations of CO 2 and other ‘ greenhouse ’ gases (Long et al. 2004). Much attention has been given to the likely impacts of the large climate changes that are expected during the rest of this century, to sugarbeet (Jones et al. 2003 ; Richter et al. 2006) and to other crops (Richter & Semenov 2005). Some of the changes to the climate are likely to have positive impacts on beet yields ; Scott & Jaggard (2000) attempted to analyse these changes. The present paper describes a more formal analysis of the climate change effects by using yield simulations made with a simulation model and with the UK daily weather records to assess the impact of climate on yield over the last three decades and compares these simulations with the UK national harvested yield and official variety trial results. The study used the Broom’s Barn Crop Growth Model (Qi et al. 2005), which has been validated and tested under different environmental conditions and for a number of cultivars. The model runs on a daily time step and is not variety-specific. It simulates : the effects of temperature on seedling emergence, the growth of foliage cover and the development of the root system down through the soil profile ; the effects of solar radiation, as intercepted by the foliage, on * To whom all correspondence should be addressed. Email: keith.jaggard@bbsrc.ac.uk Journal of Agricultural Science (2007), 145, 367–375. f 2007 Cambridge University Press 367 doi:10.1017/S0021859607006922 Printed in the United Kingdom