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Acid tolerance ranges of common freshwater organisms
Aquatic species have varying levels of tolerance for acidification, but few survive below pH values of about 5.0. View image

Adult HIV/AIDS rates in Africa, 2000
Widespread HIV infection in sub-Saharan Africa is changing the region's demographic structure and impinging on its economic performance. View image

Antarctic ozone hole, October 4, 2004
Reactions that produce ozone-destroying free chlorine atoms take place on frozen crystals in polar stratospheric clouds. View image

Arctic marine food web
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

Arctic sea ice coverage, 1979 and 2003
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

Atlantic piping plover recovery trends
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. View image

Atmospheric CO2 concentrations, 1958-2005
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

Atmospheric oxygen levels over geological time
Increases in atmospheric oxygen levels are closely correlated with hypothesized Snowball Earth episodes and with the appearance of increasingly complex life forms. View image

Atmospheric water vapor mean, 1988-1999
Because Earth is warmest near the equator, atmospheric water vapor levels are highest in tropical regions. View image

Average annual precipitation, Washington, 1971-2000
Water supplies can vary widely within a state or country depending on geography, rainfall patterns, and regional uses. View image

Biodiversity hotspots
Biodiversity hotspots cover a small fraction of Earth’s surface but are home to large numbers of living species. View image

Biome type in relation to temperature and rainfall
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

Cenozoic cooling
Sharp cooling during the Cenozoic era promoted the rise of mammals. View image

Change in asthma symptoms among children participating in HPHI before and after intervention
Controlling exposure to environmental triggers produced significant decreases in respiratory symptoms among children with asthma in three Boston public housing developments. View image

Chlorine-catalyzed ozone depletion mechanism
One chlorine atom can destroy more than 100,000 ozone molecules before it is removed from the stratosphere. View image

Circulation of air around regions of high and low pressure in the Northern Hemisphere
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

Climate forcings (W/m2): 1850-2000
Net climate forcing is the product of positive and negative forcing by many greenhouse gases, aerosols, and other contributing factors. View image

Coal formation
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

Cold water masses
Water masses with different temperatures and salinities help to drive ocean circulation. View image

Comparison between modeled and observations of temperature rise since the year 1860
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

Comparison of Venus and Earth
Venus and Earth are roughly the same size, but Venus has a much thicker atmosphere and its surface conditions are inhospitable to life. View image

Components and interactions of the global climate system
Earth's climate is a complex system influenced by sources and processes in the atmosphere, on land, and in the oceans. View image

Components of a typical flood hydrograph
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

Conceptual biogeochemical mercury cycle
Fish consumption is one of the main routes by which humans can be exposed to high levels of environmental mercury. View image

Conceptual PBPK model for hexachlorobenzene exposure
PBPK modeling integrates the physiology and anatomy of the human body with the biochemistry of specific contaminants. View image

Conditional instability
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

Confined and unconfined aquifer
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

Contaminant flow in groundwater
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. View image

Coriolis force
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

Cross-section of a hydrocarbon system
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

Current and projected freshwater stress areas
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

Cycling of carbon and oxygen
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

Dams and diversions along the Rio Grande
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

DDT accumulation in the food chain
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

Distribution of climate and soil/terrain constraints by region
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's energy balance
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's five mass extinctions
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

Earth's major land biomes
Biomes are Earth's major habitat types. They are classified according to the predominant forms of vegetation that they support. View image

Earth's marine and freshwater biomes
Marine and freshwater biomes contain many different types of habitats, from forest bogs to abyssal zones in the deep oceans. View image

Earth-atmosphere energy balance
Energy received from the Sun balances the energy that Earth loses back into space, maintaining a stable average temperature. View image

Eastern U.S. aquifers contaminated with salt water
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

Effects of cirrus and cumulus clouds on Earth's energy balance
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

Effects of groundwater pumping
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. View image

Ekman Spiral (current generated by a 10 meters/second wind at 35 degrees North)
Ekman spirals contribute to ocean current patterns. View image

Energy and nutrient transfer through ecosystems
Nutrients (shown by light arrows) cycle through ecosystems in a closed loop, while energy (shown by dark arrows) is released at each stage. View image

Exposure pathways for radioactive chemicals and materials from a nuclear waste storage facility
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

General circulation of the atmosphere
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

Geographic distribution of potential biomass energy crops
Potential energy crops could be grown in many areas of the United States that are unsuited for agriculture, providing new cash crops. View image

Geologic history of southern California.
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
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

Global circulation and climate
Each hemisphere has a number of distinct climate zones with characteristic weather patterns. View image

Global footprint (hectares/person)
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

Global GDP, 1-2001 A.D.
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

Global sea surface temperatures, July 1-4, 2005
Sunlight warms Earth unevenly, so ocean temperatures vary widely with latitude. View image

Global temperature record
This time series shows the combined global land and marine surface temperature record from 1850 through 2006. 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

Groundwater flow under the Housatonic River, Pittsfield, Massachusetts
Groundwater moves from areas of high hydraulic head to areas of low hydraulic head, so sometimes it can move upward. View image

Gulf of Mexico dead zone, July 2006
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

Hadley Centre GCM projection
Climate scientists constantly update GCMs to reflect new insights into processes that drive climate change, such as cloud formation. View image

How plants grow
Photosynthesis, respiration, and transpiration drive plant growth and development. View image

Hurricane wind patterns
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

Hydrogen fuel cell
Fuel cells use hydrogen’s chemical energy to generate electricity without emitting pollutants. View image

Hydrogen ion concentration, 2005
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

Hydropower system
Bodies of water that flow swiftly or fall rapidly from a very high point are good hydropower sources. View image

Ice sheet advance during the most recent ice age
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

Impact of acid rain on forest nutrient cycles
Long-term exposure to acid rain leaches nutrients from soil and makes plants vulnerable to nutrient deficiencies. View image

Impaired U.S. waters, 2000
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

Importance of human-produced greenhouse gases
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

Infectious diseases are affected by climate change
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

Inner city ER admissions for pediatric asthmatics
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

Label indicating that a product complies with the EU’s Restrictions on Hazardous Substances (RoHS) directive
The Restriction of Hazardous Substances Directive was adopted to reduce generation of toxic waste from discarded electrical and electronic equipment. View image

Lake Michigan food web
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

Layers of the ocean
Oceans are divided into zones that offer a wide range of conditions for life. View image

Life expectancy
Gains in life expectancy are making Social Security and medical care programs more important than ever for the well being of the elderly. View image

Life expectancy at birth, age 65, and age 75, United States, 2000
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

Marine genus biodiversity
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

Mercury in sediment profiles from straits south of Norway
Environmental mercury levels have increased dramatically since the start of the Industrial Revolution. View image

Mid-latitude cyclones along the polar front
Mid-latitude cyclones occur when warm and cold air masses collide around a center of low pressure. View image

Nonattainment and maintenance areas in the U.S. 8-hour ozone standard
Prevailing winds in North America blow from west to east. Many areas downwind of large cities suffer from high ozone pollution. View image

Normal and El Niño conditions
El Niño and La Niña affect weather and climate around the globe. View image

North Atlantic spring bloom, March 28, 2003 (Cape Cod to Newfoundland shown)
The North Atlantic spring plankton bloom starts near Bermuda and spreads north past Iceland. View image

Ocean currents
Ocean currents flow in distinct patterns generated by wind, Earth's rotation, water heat content and salinity, and bottom topography. View image

Ocean net primary productivity, 1997-2002
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

Ocean trenches and the "Ring of Fire"
The "Ring of Fire" is one of the most volcanically and seismically active regions on Earth. View image

Oxidation of iron to form rust
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 Production
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

Passenger pigeons, from John James Audubon’s Birds of America
In 1813, naturalist John James Audubon called passenger pigeons “wonderfully abundant.” A century later the species was extinct. View image

Past world population growth
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

Phenacodus, a sheep-sized herbivore found in the Eocene era
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

Plant species diversity
Many hypotheses have been proposed to explain why species richness is greater in tropical latitudes than near the poles. View image

Pleistocene glacial deposits in Illinois
Thick deposits of various glacial soils cover much of the state of Illinois. View image

Population growth rate
The pace at which population growth rates decline in coming decades will determine the peak size of Earth's population. View image

Pressurized-water reactor
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

Processes related to atmospheric composition
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

Products from a barrel of crude oil
Most petroleum products are used to produce energy, but some are used for other industrial and manufacturing purposes. View image

Profile of domestic natural gas resources
Energy resources are not static because the boundaries between recoverable and unrecoverable reserves shift as technology improves. View image

Profitability of energy efficiency upgrades
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

Ratio of working age to non-working age population
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

Relationship between judged frequency and actual number of deaths per year
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

Relative proportions of inorganic forms of CO2 dissolved in seawater
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

Risk management model
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

Roles played by soil organisms
Soil is one of the most diverse habitats on earth. Many tiny organisms play important roles in maintaining soil quality. View image

Sample geologic cross-section
Geologic cross-sections are vertical slices through rock formations. Earth scientists analyze cross-sections to map an area's geological history. View image

Satellite observations of tropospheric NO2, 2006
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 breeze
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

Sea surface salinity values
Small variations in sea surface salinity can affect ocean circulation and the water cycle. View image

Simplified model of a primary cell wall
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

Size comparisons for aerosol pollution
Some particles are large enough to see with the naked eye, while others can only be viewed under an electron microscope. View image

Snow's original map (shows cases of cholera around water pumps)
Mapping has become a standard technique in epidemiology, using statistical methods to account for variations in population density. View image

Structure of the atmosphere
Atmospheric pressure decreases exponentially as altitude increases, while temperature rises with altitude in some layers and decreases in others. View image

Surface air temperature increase, 1960 to 2060
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

Switchgrass can grow up to 12 feet tall and has deep roots that stabilize soil and sequester large amounts of carbon. View image

Techniques for reducing home radon gas levels
Radon exposure, which kills thousands of Americans annually, can be prevented by testing homes and making repairs where radon is detected. View image

Terrestrial habitat transformation
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

Terrestrial net primary productivity
Many factors influence primary productivity rates, but the most important on land are temperature and water availability. View image

The biological pump
The biological pump transfers carbon from the atmosphere to deep ocean sinks. View image

The breakup of Rodinia
Rodinia was Earth's main land mass from about 1.2 billion to 750 million years ago, surrounded by a single planetary ocean. View image

The demographic transition
The demographic transition is a widely-observed phenomenon, although its onset and duration vary by country. View image

The electromagnetic spectrum
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

The faint, young sun and temperatures on Earth
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

The geochemical carbon cycle
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

The geochemical carbon cycle on a Snowball Earth
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
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

The global carbon cycle
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

The nitrogen cycle
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

The phosphorus cycle
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. View image

The risk assessment/risk management paradigm
Assessing and managing risks are two distinct steps, each of which involves multiple decisions. View image

The universal Tree of Life
As the Tree of Life shows, microbes were the dominant early life forms on Earth. View image

The water cycle
The water cycle is essentially a closed loop, but water can be diverted from one sink to another or contaminated as it cycles. View image

The world's largest cities in 2015
The world's largest cities will increasingly be located in less-developed countries. View image

Thermohaline circulation
The thermohaline circulation is a global current that moves water between ocean basins and from the surface to ocean depths. View image

Three domains of life
Although Earth’s most complex life forms are Eukarya, the microbial world contains much of our planet’s biodiversity. View image

Time table of the evolution of complex life forms on Earth
Complex life forms appeared on Earth relatively late in geologic time, but diversified rapidly. View image

Total fertility rate
In many less-developed countries, declining fertility rates over the past 50 years represent an important population success story. View image

Total ozone mapping spectrometer (TOMS) aerosol index of smoke and dust absorption, 2004
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

Typical forest succession pattern
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

U.S. certified organic acreage
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

U.S. CO2 emissions from fossil fuel (by sector and fuel type)
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

U.S. Economic Growth and Criteria Pollutant Emissions, 1970-2006
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

U.S. geothermal resources (estimated temperature at 6 kilometers depth)
Most geothermal energy production in the United States today is in California, Utah, Nevada, and Hawaii. View image

Vostok ice-core CO2
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

Water in the ground
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

Watercolor painting of Ivory-billed Woodpeckers by John James Audubon
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

Western Hemisphere locations for the Christmas Bird Count
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

Winds around highs and lows
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

World cereal production
Cereals are the primary source of animal feeds and non-meat calories for humans worldwide. View image

World CO2 emissions from fossil fuel use in 2000 (by sector)
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

World energy use by fuel source
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, 1961-1996 (measured as the sum of cereals, coarse grains, and root crops)
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

World freshwater supplies
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

World marketed energy consumption, 1980-2030
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

World population
World population is rising, but the rate of increase is declining as less-developed countries pass through the demographic transition. View image

X-ray fluorescence intensity from Pb in hair
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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