A number of different physical variables impact agriculture. These include temperature, precipitation, humidity, wind speed, and radiation. The absolute levels of these variables and their variability on a daily, monthly, and annual basis, affect crop yields as well as livestock health.
Crops are particularly sensitive to absolute temperature variation even over short time scales, in some cases a few hours (for extreme cold) and days (for warmth). Likewise, extreme events such as floods, and inter-annual variations in rainfall connected with cycles such as ENSO can also impact crops significantly. For example, the major drought in Australia from 1998-2010 led to significantly lower crop yields. Major cold snaps in Florida in 1983 and 1985 killed a third of all citrus trees with an accompanying loss of $2 billion. At the other end of the spectrum, the North Atlantic Oscillation has caused sunnier summers in Britain, leading to increased wheat yields.
As it turns out, anthropogenic impacts can greatly magnify the effects of climate change on crops, livestock, and fisheries. For example, soil erosion, overgrazing, air pollution, salinization of groundwater, and pests and overuse of pesticides tend to exacerbate the impacts of changing climate such as droughts and heat waves. Here, we describe the forecasts and impacts of changes in climate variables, followed by anthropogenic changes.