Farmers observe climate change first hand. They see spring warmth arrive earlier or the autumnal frost arrive later. They see how plants bud, leaves open and vegetation grows earlier. Thus, flowers bloom nine days earlier than they did thirty years ago in Europe, North America and Japan. On certain French farms, corn can now be sown 20 days earlier than 30 years ago.
How does this affect yields? Global warming makes people like wine-growers happy. In Alsace, for example, the number of days that favour vine growth – days on which the average temperature is higher than 10°C – increased from 170 in 1970 to 210 in 2000. And, globally, in Europe and in the United States, wine has become more stable and its quality has improved. For forestry, the growth of forests seems to have increased between +6 and +12 % over the past two decades, depending on the region. This is because the temperature is increasing but also because the increase in CO2 concentration has a direct positive effect on the growth of vegetation.
This is not the case of all crops. Sometimes, a one degree increase is enough to reduce the yield of paddy fields by 15% as has been observed in the Philippines. In countries that are already affected by droughts, the increase in temperature combined with a decrease in rain no longer makes it possible for local varieties to finish growing. This is the case of the peanut. It is grown in Sahelian countries where it is a staple food but its production is decreasing.
To this day, the effects of global warming are slight and difficult to pinpoint in regards to the significant changes the agricultural field has experienced over the past decades. These changes have been driven by mechanisation, chemistry and biotechnologies. However, as the increase in yields is slowing down and global warming is increasing, the situation could change.