the vegetation in Earth’s ecosystems. Commercial farmers may also use land surface temperature maps like these to evaluate water requirements for their crops during the summer, when they are prone to heat stress. Conversely, in winter, these maps can help citrus farmers to determine where and when orange groves could have been exposed to damaging frost. NDVI July 2011: July 2011: Satellites observe global-scale patterns of vegetation that scientists use to study changes in plant growth as a result of climate and environmental changes as well as human activity. Photosynthesis plays a big role in removing carbon dioxide from the atmosphere and storing it in wood and soils, so mapping vegetation is a key part of studying the carbon cycle. Farmers and resource managers also use satellite-based vegetation maps to help them monitor the health of our forests and croplands. On this map, vegetation is pictured as a scale, or index, of greenness. Greenness is based on several factors: the number and type of plants, how leafy they are, and how healthy they are. In places where foliage is dense and plants are growing quickly, the index is high, represented in dark green. Regions where few plants grow have a low vegetation index, shown in tan. The index is based on measurements taken by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite. Ocean Temp AVHRR: Temp AVHRR: Sea surface temperature is the temperature of the top millimeter of the ocean's surface, which scientists call the "skin temperature." Like Earth's land surface, sea surface temperatures are warmer near the equator and colder near the poles. Currents like giant rivers move warm and cold water around the world's oceans. Some of these currents flow on the surface, and they are obvious in sea surface temperature images. Ocean temperatures influence weather, including hurricanes, the productivity of marine plant and animal life, and the rate at which carbon dioxide in the air dissolves in the waters of the ocean. Over long periods of time, changes in sea surface temperature are indicators of natural and human-caused climate change. Changes in ocean surface temperatures have a huge impact on weather and land. For example, when the full width of the Pacific heats up along the equator, an El Niño develops. El Niño alters rainfall patterns around the globe, causing heavy rainfall in the southern United States and severe drought in Australia, Indonesia, and southern Asia. On a smaller scale, ocean temperatures influence the development of tropical cyclones (hurricanes and typhoons), which need warm ocean waters to form and grow. Ocean temperatures also influence how quickly tiny ocean plants can grow. Since the plants absorb carbon dioxide as they turn sunlight into energy, they influence how much carbon dioxide the oceans can soak up. Scientists who want to measure how much carbon dioxide is in the atmosphere and how much is absorbed by plants are interested in the connection between sea surface temperatures and ocean plant growth. These data have been collected since 1981 by a series of National Oceanic and Atmospheric Administration (NOAA) satellites. Ocean Temp MODIS: Temp MODIS: Sea surface temperatures have a large influence on climate and weather. For example, every 3 to 7 years a wide swath of the Pacific Ocean along the equator warms by 2 to 3 degrees C. This warming is a hallmark of the climate pattern El Niño, which changes rainfall patterns around the globe, causing heavy rainfall in the southern United States and severe