Our Home Planet
Earth is an ever-changing place. How much do you know about your home planet?
The Landsat satellite, a joint mission between NASA and the U.S. Geological Survey, can detect both visible and infrared light that are reflected off the surface of the Earth. This light allows us to measure the heat radiating from land that has been burned, assess how much plants are photosynthesizing to make food and distinguish coral reefs from other landforms across the globe.
The Northern Hemisphere contains more than twice the amount of land. While the Northern Hemisphere is almost 40 percent land and 60 percent water, the Southern Hemisphere is about 20 percent land and 80 percent water.
Phytoplankton thrive on sunlight and nutrients. Winds over the ocean help bring up nutrient-rich water from the deep ocean by driving currents away from the coast and equator. The warmer the surface waters become, the less mixing there is between those waters and deeper, more nutrient-rich water. As nutrients become scarce at the surface, where phytoplankton grow, productivity declines. El Niño reduces the amount of nutrient-rich water brought to the surface and therefore the amount of phytoplankton, while La Niña does the opposite and is characterized by more phytoplankton than normal.
Gravity is determined by mass. Earth’s mass – for example, mountain ranges, ice caps and water stored underground – is not distributed equally and changes over time. The Gravity Recovery and Climate Experiment (GRACE) satellites, a collaborative mission involving NASA, are tracking Earth’s gravitational field in unprecedented detail and tell us that the Earth’s ice sheets are melting at an alarming rate of 300 billion tons per year.
Earth's ice sheets and glaciers are made up of thousands of years of accumulated snowfall tightly compacted into ice. Snow located on top of sea ice offers important habitats for animals such as seals that use the snow to hide their young from predators. Snowfall on mountains and its subsequent melt increases stream flow and provides people all around the world with vital freshwater.
Today, over half of the world’s population lives in cities and urban areas and this is predicted to grow to 67 percent by 2050 (United Nations 2012). However, urban regions still cover only about 3 percent of the Earth’s total land area. Ever since their emergence, cities have been important hubs of economic, social and political activity, but such activity can come at a price for the environment, for example through pollution and the loss of natural ecosystems. Scientists are working to better understand the impacts of future climate change on city dwellers.
Although most aerosols reflect sunlight, some also absorb it. An aerosol’s effect on light depends primarily on the composition and color of the particles. Broadly speaking, bright-colored or translucent particles tend to reflect radiation in all directions and back towards space, cooling the atmosphere. Examples are sulfates, nitrates and salt particles. Darker aerosols – like soot particles, or “black carbon” – can absorb significant amounts of light, warming the atmosphere but also shading the surface.
As the planet warms up, the world’s average sea level is rising. Since 1993, when the satellite data record began, average sea level has risen by over 3 mm per year. This is the result of both the global warming-related expansion of ocean waters as well as the melting of land ice around the world. Although all of Earth's oceans are interconnected, sea level and sea level rise can vary significantly from one place to another. In Greenland, for example, as the ice sheet melts the ground will actually rise somewhat when the weight of ice on top of it is reduced.
The vast majority of tropical glaciers — over 99 percent – are found in the Andes nations of Bolivia, Colombia, Ecuador and Peru. Even though glaciers are normally associated with cold regions of the world, tropical glaciers also exist in Earth’s equatorial mountain ranges where the elevation is high enough and it is cold enough for ice to accumulate. Tropical glaciers are also found at the tops of mountains in Indonesia, Venezuela, Peru, Mexico, Iran as well as the Alps, Himalayas and Rocky Mountains.
Some of the fastest-warming regions on the planet include Alaska, Greenland and Siberia. These Arctic environments are highly sensitive to even small temperature increases, which can melt sea ice, ice sheet and permafrost, and lead to changes in Earth’s reflectance (or “albedo”).