Chapter 4 Section 1: ClimateWhen you think about climate, you might think of dramatic headlines: “Hurricane Katrina floods New Orleans!” or “Drought parches the Southeast!”But big storms and seasonal droughts are better described as weather rather than climate.What is climate, and how does it differ from weather? How do climate and weather affect organisms and ecosystems?What is climate?
What factors determine global climate?Global climate is shaped by many factors, including solar energy trapped in the biosphere, latitude, and the transport of heat by winds and ocean currents.The main force that shapes our climate is solar energy that arrives as sunlight that strikes Earth’s surface.Some of that energy is reflected back into space, and some is absorbed and converted into heat. Some of the heat also radiates back into space, and some is trapped in the biosphere.The balance between heat that stays in the biosphere and heat lost to space determines Earth’s average temperature. Earth’s temperature is largely controlled by concentrations of three atmospheric gases—carbon dioxide, methane, and water vapor.These “greenhouse gases” function like glass in a greenhouse, allowing visible light to enter but trapping heat through a phenomenon called the greenhouse effect. If greenhouse gas concentrations rise, they trap more heat, so Earth warms. If their concentrations fall, more heat escapes, and Earth cools.Without the greenhouse effect, Earth would be about 30°C cooler than it is today. Near the equator, solar energy is intense, as the sun is almost directly overhead at noon all year. That’s why equatorial regions are generally so warm.The curvature of Earth causes the same amount of solar energy to spread out over a much larger area near the poles than near the equator. Earth’s polar areas annually receive less intense solar energy, and therefore heat, from the sun.The difference in heat distribution creates three different climate zones: tropical, temperate, and polar.