Growing season for agricultural crops (CLIM 030) - Assessment published Nov 2012

Key policy question: How is climate change affecting the growing season for agricultural crops?

Change in the number of frost-free days per year

Note: This figure shows the rate of change in the growing season length (defined as the number of frost-free days per year) during the period January 1975 – December 2010.

Data source:

• Rate of change of frost-free period map for Europe provided by Geo network - open source

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Key assessment

Past trends

Increasing air temperatures are significantly affecting the duration of the growing season over large areas of Europe [i]. Many studies report a lengthening of the period between the occurrence of the last spring frost and the first autumn frost. This has occurred in recent decades in several areas in Europe and more generally in the Northern Hemisphere [ii]. Studies of changes in the growing season based on remote sensing show a diverse spatial pattern in Europe [iii]. Across all of Europe, the delay in end of the season of the period 1992–2008 by 8.2 days was more significant than the advanced start of the season by 3.2 days [iv].

An analysis of the frost-free period in Europe between 1975 and 2010 shows a general and clear increasing trend. The trend is not uniformly spread over Europe. The highest rates of change (larger than 0.8 days per year) were recorded along the Atlantic shores, in the British Isles, Denmark, central parts of Europe, central Italy, central and southern Spain, and in Turkey (Figure 1). There are also areas in Europe with an apparent trend for reductions in the frost-free period; however, these trends are not significant.

Projections

A warming of the climate is expected mainly to result in an earlier start of the growing season in spring and a longer duration in autumn [v]. A longer growing season allows the proliferation of species that have optimal conditions for growth and development and can thus increase their productivity or number of generations (e.g. crop yield, insect population). This will in many cases also allow for introduction of new species previously unfavourable due to low temperatures or short growing seasons. This is relevant for introduction of new crops, but will also affect the spreading of weeds, insect pests and diseases [vi].

A further lengthening of the growing season as well as a northward shift of species is projected as a result of the projected further increase in temperature across Europe [vii]. The date of last frost in spring is projected to advance by about 5–10 days by 2030 and by 10–15 days by 2050 throughout most of Europe [viii]. The suitability for growing certain crops will also depend on the total amount of heat received during the growing season expressed as a temperature sum. Projections show the greatest absolute increases in temperature sum in southern Europe, whereas relative changes are much larger in northern than in southern Europe [ix].

The extension of the growing season is expected to be particularly beneficial in northern Europe, where new crops could be cultivated and where water availability is generally not restricting growth [x]. In parts of the Mediterranean area the cultivation of some crops may shift from the summer season to the winter season, which could offset some of the negative impacts of heat waves and droughts during summer [xi]. Other areas of Europe, such as western France and parts of south-eastern Europe, will experience yield reductions from hot and dry summers without the possibility of shifting the crop production into the winter seasons.

[i] H. Scheifinger et al., „Trends of spring time frost events and phenological dates in Central Europe“, Theoretical and Applied Climatology 74 (Januar 1, 2003): 41–51, doi:10.1007/s00704-002-0704-6.

[ii] M Trnka et al., „A 200-year climate record in Central Europe: implications for agriculture“, Agronomy for Sustainable Development 31 (Juni 7, 2011): 631–641, doi:10.1007/s13593-011-0038-9.

[iii] Mark D Schwartz, Rein Ahas, and Anto Aasa, „Onset of Spring Starting Earlier Across the Northern Hemisphere“, Global Change Biology 12, Nr. 2 (Februar 1, 2006): 343–351, doi:10.1111/j.1365-2486.2005.01097.x.

[iv] Su‐jong Jeong et al., „Phenology Shifts at Start Vs. End of Growing Season in Temperate Vegetation over the Northern Hemisphere for the Period 1982–2008“, Global Change Biology 17, Nr. 7 (Juli 1, 2011): 2385–2399, doi:10.1111/j.1365-2486.2011.02397.x.

[v] Jeong et al., „Phenology Shifts at Start Vs. End of Growing Season in Temperate Vegetation over the Northern Hemisphere for the Period 1982–2008“.

[vi] Jonas Roos et al., „The impact of global warming on plant diseases and insect vectors in Sweden“, European Journal of Plant Pathology 129 (Oktober 2, 2010): 9–19, doi:10.1007/s10658-010-9692-z.

[vii] J.E. Olesen et al., „Impacts and adaptation of European crop production systems to climate change“, European Journal of Agronomy 34, Nr. 2 (Februar 2011): 96–112, doi:10.1016/j.eja.2010.11.003.

[viii] M. Trnka et al., „Agroclimatic Conditions in Europe Under Climate Change“, Global Change Biology 17, Nr. 7 (Juli 1, 2011): 2298–2318, doi:10.1111/j.1365-2486.2011.02396.x.

[ix] Trnka et al., „Agroclimatic Conditions in Europe Under Climate Change“.

[x] Olesen et al., „Impacts and adaptation of European crop production systems to climate change“.

[xi] M. I. Minguez et al., „First-order impacts on winter and summer crops assessed with various high-resolution climate models in the Iberian peninsula“, Climatic Change 81, Nr. Supplement 1 (2007): 343–355, doi:10.1007/s10584-006-9223-2.