extreme weather events also have a negative impact on agricultural production recent food price spikes and supply shortages caused by exceptional conditions of drought in the russian federation ukraine and countries in east africa as well as floods in pakistan australia and the united states are prima facie evidence of the catastrophic impacts of adverse climatic conditions possibly related to climate change for instance it is estimated that in africa and south asia average crop yields could fall by percent and fisheries by percent by knox et al while yields may increase in some high latitude areas such as china and the uk overall decreases are predicted to offset any increases even with only moderate warming knox et al