Agricultural technology has increased so much in the past few decades that any changes that have resulted from rising temperatures and CO2 levels are not easily discernable. Small adjustments that farmers make due to temperature increases have likely been absorbed by all the other changes. Yet some recent adaptations to warmer temperatures have been seen in agriculture.

The number of frost--free nights has increased in the temperate regions, resulting in a one week longer growing season in parts of North America relative to a few decades ago. Crop yields in the temperate regions, where developed nations are largely located, have increased. In Europe, particularly at high latitudes, farmers have adapted to environmental changes by planting their crops earlier. In Germany, for example, the advance has been 2.1 days per decade between 1951 and 2004. However, longer growing seasons are not uniformly good. In the south of France, apricot trees now flower one to three weeks earlier than in past decades, putting them at risk for spring frost and bud necrosis.

Arid regions have tended to become warmer and drier, and wet regions have become even wetter. As a result, crop yields have grown in wet regions but shrunk in arid regions. The loss of crops due to a reduction in rainfall is intensified by the expansion of insect ranges and increased forest fires. Another hazard in the drier areas is desertification, the process by which dry air evaporates moisture from the soil and the land turns to desert. Where possible, farmers in arid lands increase the amount of irrigation, but where this is not possible, land that was once farmable is lost.

More extreme weather events are affecting agriculture, even in the developed nations. In the United Kingdom, drought has caused farm--ers to increase the percentage of crops they irrigate. The European

An extremely dry village in sub-Saharan Africa. (peeterv/ iStockphoto)

heat wave of 2003 decreased crop yields by up to 30% in some nations, including Greece, Portugal, Italy, and especially France.

Little is known about the effects of climate change on subsis--tence agriculture. In the Sahel in sub--Saharan Africa, where farm--ing is extremely marginal, higher temperatures and lower rainfall have reduced the chance that the strains of plants that are currently being grown are able to complete their life cycle. Some rice--growing regions in Southeast Asia appear to be undergoing a slight decrease in productivity.

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