Nearly 150 million kilometers separate the sun and earth, yet solar radiation drives earth's weather and atmosphere. Most atmospheric gases extend only 30 km above the surface, where most weather occurs within the lower 10-15 km. The greenhouse gases of water vapor and carbon dioxide warm the atmosphere by absorbing and emitting infrared radiation. Human and natural activities release aerosols and pollutants into the atmosphere that impact weather and climate patterns. Meteorologists study weather using both satellite instruments that observe large-scale patterns and ground-based tools that measure local conditions.