Why do plants produce their own food

Scientists have noted that at present the earth is closest to the sun in january and farthest from the sun in july. the reverse will be true in 13,000 years and theearth will then be closer to the sun in july than january. how does earth's current proximity to the sun affect the climate in the northern hemisphere? winters are cooler and summers warmer because of the closer proximity of the earth to the sun.winters are warmer and summers cooler because of the closer proximity of the earth to the sun.winters are shorter and summers longer because of the closer proximity of the earth to the sun.winters are longer and summers shorter because of the closer proximity of the earth to the sun