The communities that form the base of Arctic marine food chains are uniquely adapted to conditions under the ice, including wide fluctuations in light, temperature, and salinity levels, and constant change in the extent and thickness of ice cover. View image
According to NASA, Arctic perennial sea ice has been shrinking by 9 percent per decade since the 1970s. This process creates a positive climate feedback by reducing the amount of solar radiation that is reflected back into space from Earth's surface. View image
Piping plovers nest and feed on outer beaches along the Atlantic coast. Coastal development, human disturbance, and harassment from pets are major threats to plovers.
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Charles David Keeling measured CO2 concentrations at Mauna Loa Observatory in Hawaii, more than 11,000 feet above sea level, to obtain data that did not include emissions from nearby vegetation or human activities. His measurements show a steady rise in atmospheric CO2 concentrations over 47 years. View image
Increases in atmospheric oxygen levels are closely correlated with hypothesized Snowball Earth episodes and with the appearance of increasingly complex life forms. View image
Biome distribution is closely associated with climate. Each of the biomes shown in this figure represents a different combination of temperature and precipitation ranges. View image
Controlling exposure to environmental triggers produced significant decreases in respiratory symptoms among children with asthma in three Boston public housing developments. View image
Air moves toward low-pressure regions and away from high-pressure regions. The Coriolis force deflects these air masses in opposite directions around high and lows. View image
During the Carboniferous Period, from about 354 to 290 million years ago, Earth's climate was tropical and humid. Plant material buried in swamps formed rich coal deposits in what are now Europe, Asia, and North America. View image
Climate models produce the best match for current trends when they are programmed to simulate both natural and manmade factors that drive climate change. View image
Perennial streams that flow year-round have a high baseflow component, but quickflow (runoff over land after storms) can substantially increase their flow patterns. View image
When conditional instability exists, air parcels are stable if they are dry and unstable if they are saturated. Conditional instability can help to generate storms by causing parcels of moist air to rise and form towering clouds. View image
Unconfined aquifers receive recharge directly from rainfall and surface water infiltrating downward. Confined aquifers are connected to unconfined areas where water can flow in. View image
Mapping how a contaminant plume will migrate once it reaches groundwater requires understanding of the pollutant's chemical properties, local soil characteristics, and how permeable the aquifer is.
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The Coriolis force is created by Earth's rotation, which deflects air masses as they move over long distances. It is strongest near the poles and nonexistent at the equator. View image
Predicting the location, type, and quality of hydrocarbon systems is critical to successful oil and gas development. Technology, such as seismic imaging and computer modeling, has improved the process in recent decades. View image
Areas with good freshwater endowments are still vulnerable to freshwater stress if they withdraw water from reserves more quickly than it is replenished. View image
Photosynthesis removes CO2 from the air and adds oxygen, while cellular respiration removes oxygen from the air and adds CO2. The processes generally balance each other out. View image
The Rio Grande River is heavily managed for irrigation, flood control, power generation, and recreation. Low water levels have concentrated pollutants in river water, and the lower Rio Grande has become increasingly saline. View image
Use of DDT was banned in the United States in 1972 because of its persistence, its tendency to bioaccumulate, and its adverse impacts on reproduction, especially in birds. View image
Climate, soil quality, and terrain significantly limit where crops can be grown productively. Some of these constraints can be mitigated with inputs like irrigation and fertilizer, and with techniques that manage land resources on a sustainable basis. View image
Earth constantly absorbs energy from the sun and radiates energy back to space. Normally these processes balance each other, but human-driven emissions of greenhouse gases are altering the balance by retaining more heat in the atmosphere. View image
Earth has experienced five major mass extinctions in the past half-billion years. Although it is not reflected on this graph, scientists think a sixth mass extinction may be under way. View image
Withdrawing freshwater from coastal aquifers can cause saltwater to intrude into the aquifers. This problem is likely to increase in areas where coastal development is expanding. View image
Cirrus clouds permit most of the sunlight that reaches them to pass through to Earth's surface, while thicker cumulus clouds reflect much of the sunlight that strikes them back into space. Both types block some of the heat radiating from Earth, warming the planet's surface. View image
Excessive groundwater pumping can lower the water table, deplete nearby rivers and streams, and cause land to subside as water is pulled from soil and the soil collapses and compacts.
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Humans can be exposed to environmental pollutants by many routes, so researchers need to know how contaminants move through various media such as air, water, and soil. View image
Differential heating of Earth produces distinct patterns of rising and descending air masses, winds, and storms in well-defined cells around the globe. View image
Scientists study characteristics of a geologic stratum such as color and mineral type so that they can match up portions of that stratum that are exposed in separate regions. Strata can extend for many miles, although they may only be exposed in a few places. View image
Geostrophic flow is more common in the upper atmosphere than at the surface, where friction between air and land slows the movement of air parcels. View image
The amount of biocapacity available per person is the amount of bioproductive land and sea divided by the total human population (6.6 billion in 2007) - 1.7 ha per person. View image
One measure of economic output is GDP, or gross domestic product - the market value of goods and services produced in a given region in a year. View image
Gondwanaland started to fragment and drift apart during the Mesozoic era, eventually creating the modern continents. This process changed ocean circulation patterns and altered Earth's climate. View image
The Gulf of Mexico hypoxic zone, which occurs in an important commercial fishing region, forces fishermen to travel farther to find live fish and shellfish. View image
Hurricane wind speeds range from 74 miles per hour (the minimum for a Category 1 storm on the Saffir/Simpson scale) to more than 155 miles per hour for Category 5 storms. View image
Acid rain is most severe in the midwestern and northeastern United States because the Midwest has a large number of coal-burning power plants that send SO2 and NOx emissions eastward. View image
As recently as 15,000 years ago, during the Wisconsin Glaciation, ice sheets extended south into what are now the Midwestern states. Many North American landscape features, including Cape Cod, Long Island, and the Great Lakes, were shaped by this series of glacial advances and retreats. View image
U.S. waters are considered impaired if they cannot fully support their aquatic biological communities or other designated uses or conform to guidelines set by states, territories, or tribal governments defining fishable and swimmable water quality. View image
CO2 is the most important anthropogenic greenhouse gas, but other gases also make significant contributions to climate change. Other pollutants, such as fine particulates, also affect how much solar radiation is retained in Earth's atmosphere. View image
Infective agents and their vector organisms are sensitive to factors such as temperature, surface water, humidity, wind, soil moisture, and changes in forest distribution. View image
Children living in poor sections of inner cities are 5 times more likely to be hospitalized for asthma than children living in wealthier sections. View image
The Restriction of Hazardous Substances Directive was adopted to reduce generation of toxic waste from discarded electrical and electronic equipment. View image
Food webs illustrate the complicated feeding patterns within ecosystems, in which a single species may consume a variety of other creatures and in turn serve as prey for multiple predators. View image
Life expectancy for a female born in the United States in 2004 was about 80 years, but a woman who already lived to age 75 at that point would have survived vulnerable phases in her earlier life and could be expected to live well into her 80s. View image
This graph shows the fraction of marine genera that were present in an interval of time but did not exist in the following interval. It includes a selection of marine organisms that were easily preserved as fossils, not the entire inventory of living species. View image
In contrast to land, where vascular plants carry out most primary production, most primary production in the oceans is done by microscopic algae. View image
In oxidation reactions such as rust formation, a molecule or atom loses electrons and becomes more positively charged. Although it can also take place with other chemicals, oxidation is so named because the first such reactions to be thoroughly studied were reactions with oxygen. View image
Ozone is produced in the upper stratosphere by intense ultraviolet radiation, which breaks oxygen molecules into oxygen atoms that react with oxygen molecules to form ozone molecules. View image
Before the 19th century, world population grew very slowly because high fertility was offset by high mortality. Improvements in population health, triggered partly by the industrial revolution, ushered in a period of rapid population growth. View image
Warm temperatures during the Eocene era favored smaller mammals, whose bodies were better able to manage heat than those of larger mammals that preceded them. View image
Pressurized-water reactors, so named because the water in the primary coolant loop is circulated under pressure to keep from boiling, are widely used around the world. View image
A range of gases and particulate materials are constantly mixing and interacting in the atmosphere. Some effects from these pollutants are felt at the local level, while others are regional or global. View image
Owners have many options for making their homes more energy-efficient. Home energy audits, which some energy suppliers offer to customers at no charge, can help owners set priorities for improvements. View image
Many developing countries have an opportunity to reap a demographic dividend in the coming decades if they can provide education and job opportunities for young workers. View image
Many people overestimate risks from high visible and sensational threats like tornadoes and underestimate risks from common illnesses such as cancer and heart disease. View image
Under current conditions bicarbonate is the most abundant form of CO2. All three forms are important for biological processes carried out by marine organisms. The green arrows in this diagram show the range of pH (7.5 to 8.5) that is likely to be found in the oceans now and in the future. View image
Judging risks in terms of both their probability and their likely consequences can make risk management more systematic and can help regulators focus time and resources on the most urgent risks. View image
Geologic cross-sections are vertical slices through rock formations. Earth scientists analyze cross-sections to map an area's geological history. View image
Global NOx emissions are increasing, driven by rising demand for energy and transportation. NOx contributes to many air pollution problems, including ground-level ozone, smog, acid rain, and climate change. View image
Sea breezes are caused by temperature differences between land at the surface and adjoining water, which cause air to flow in opposite directions during the day and at night. View image
Cellulose, hemicellulose, and lignin (not shown) are closely associated in plant cell walls. This structure makes it difficult for glucose molecules to be fermented into fuel. View image
Atmospheric pressure decreases exponentially as altitude increases, while temperature rises with altitude in some layers and decreases in others. View image
Global climate models calculate many variables that affect Earth's climate, such as air and ocean temperatures, cloud distribution, the size of polar ice caps, and the amount of solar radiation that the atmosphere absorbs and reflects. As the figure shows, climate change is projected to affect all regions of Earth, with the most extreme impacts near the poles. View image
Between 40 to 80 percent of many habitat types may be converted for human use by 2050. The projected gain in temperate forest lands is due to reforestation on land formerly cleared for farms. View image
The Sun is much hotter than Earth, so it emits radiation at shorter wavelengths. The solar spectrum x 10-6 applies at the surface of the Sun, not at Earth's orbit. Solar energy flux is lower by a factor of 50,000 at Earth's orbit. View image
Based on the strength of the young sun, the early Earth should have been frozen over. However, greenhouse gases in Earth's atmosphere retained enough heat to provide liquid water on Earth's surface. View image
A silicate weathering feedback adjusts atmospheric CO2 sources and sinks. Plate tectonics recycle sedimentary carbon (carbonate and organic matter) as volcanic and metamorphic CO2. View image
On a Snowball Earth, volcanic and metamorphic CO2 sources are unaffected, but the absence of rainfall reduces CO2 removal from the atmosphere. Ice cover and cold ground temperatures reduce silicate weathering. View image
The geologic time scale divides Earth's history into blocks of time that are ordered sequentially and read from bottom to top, like the rock records on which it is based. View image
Carbon cycles constantly between land, oceans, and the atmosphere, although its residence time in various reservoirs can vary greatly. Black arrows in this image show natural fluxes and red arrows show anthropogenic contributions. View image
Nitrogen is abundant in the atmosphere but occurs in an inert form that living organisms cannot use directly. In the nitrogen cycle, some of this supply is converted to biologically useful forms. View image
Phosphorus is found in water, soil, and sediments. Like nitrogen, it must be converted to biologically useful forms before plants and animals can take it up.
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Major fine aerosol sources include fossil fuel and biomass combustion and high-temperature industrial processes. Industrialization in Asia is producing high levels of aerosol pollution. View image
Left undisturbed, an abandoned field will regrow from a meadow into a scrub community, then become populated by pines and ultimately by hardwood trees. View image
Organic farming accounts for a small fraction of land under cultivation worldwide, but interest in organic methods is rising. Organically grown products typically earn significant market premiums over conventional crops. View image
Electricity is extensively used in the U.S. because the industry is organized to provide reliable energy across long distances from many energy sources. Many of these energy sources produce carbon dioxide emissions. View image
Major pollutant emissions have trended downward on the whole in most industrialized nations since national governments began to adopt controls in the 1970s. View image
This ice core data from Russia's Vostok research station at the center of the East Antarctic Ice Sheet shows atmospheric CO2 concentrations dating back more than 400,000 years. View image
Groundwater is water flowing through the saturated zone underground where all pores, cracks, and spaces between rocks and soil particles are filled with water. View image
Reported sightings of Ivory-billed Woodpeckers over the past several years have raised hopes that habitat conservation measures could still preserve the species. View image
The annual Audubon Christmas Bird Count started in 1900 as an alternative to traditional Christmas Day hunting contests. Today more than 50,000 volunteers take part yearly. View image
Sinking air near high-pressure systems inhibits the formation of clouds, so highs are associated with clear, dry weather. Rising air near low-pressure systems produces clouds and rain. View image
The emissions of the majority of electricity production, of all refining, and of 80% of industry are caused by a restricted number of intensive sources, and therefore eligible for a capture and sequestration process. View image
Most of the energy used worldwide today comes from fossil fuels. Other sources include non-hydropower renewable energy such as solar, geothermal, and wind power. View image
World food production grew at unprecedented rates in the second half of the 20th century, increasing available food supplies in most regions except for sub-Saharan Africa. View image
Some countries receive enormous amounts of rainfall, while others receive virtually none or get most of it during a brief rainy season. These imbalances contribute to the unequal distribution of world water supplies. View image
This is EIA’s “reference case” scenario, which assumes that current laws and policies remain unchanged. Many factors, including economic growth rates, world oil prices, and energy intensity (the ratio of energy use to gross domestic product) could alter these projections. View image
Composer Ludwig von Beethoven suffered from lifelong symptoms that included abdominal pain, irritability, and depression. Lead poisoning could account for these symptoms, and may have contributed to his early death at 57. View image
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