Population

In the last few generations it has become obvious that human beings are one of the major factors in modifying the surface of the Earth.

• The numbers of people have increased. In 1939 the population was about 2,166,231,000. Now it is 6,054,680,530. This is an increase of about 180%. At this rate there will be 12 billion in 40 years, 24 billion in 80 years, and 48 billion in 120 years.
• One view of population increase is that it is exponential - which means that the rate of increase is a function of the amount present. Another is logistic - in which population increases until it reaches some carrying capacity limit and then it stabilizes. Carrying capacity depends on the technology - tools, agriculture, industry. Each has provided an increase in capacity but then a limit was reached.

 Figure 2 shows population increase by region.

Human induced changes in Earth's environment include alterations in climate, land productivity, water resources, ocean and atmospheric chemistry, and ecological systems.

With the start of agriculture (~10,000 years ago), with the discovery of metal and metalworking about 7,500 years ago, and with the development of the plow and irrigation about 5,500 years ago, people were poised to begin role as agents geologic change.

More than half the carbon put into the atmosphere as carbon dioxide (CO2) and methane (CH4) is absorbed by the ocean, plants and soils as organic compounds, fossil fuels and carbonate rocks (Fig. 3). The rest lingers in the atmosphere where it traps heat leading to warming.  

• Some of the carbon is stored for a medium term in soils and for the long term in the Earth as carbonate (CO₃^-) rock such a limestone or as fossil fuels (gas, oil and coal).
• Other amounts of carbon are in the short term carbon cycle that involves plant removal of carbon gases from the atmosphere by photosynthesis, transfer of the carbon to predators, and return of the carbon by respiration.

Human beings contribute to the addition of carbon into the atmosphere by destroying forests and other plant communities that extract carbon from the atmosphere

• by burning fossil fuels and
• by making cement and lime from limestone.

These effects result in an increase in the carbon content of the atmosphere because they add to the natural carbon cycling. Also the rate at which human beings transfer carbon stored in the Earth into the atmosphere is much faster than would occur without human intervention.

Current patterns of energy use have destructive impacts on land and natural resources, climate, air quality, rural and urban settlements, and human health and well-being. Among these are carbon emissions, and oxides of nitrogen and of sulfur (Fig. 7). The latter are major components of acid rain.

The need for ever higher levels of energy to fuel economic development in all regions of the world and the absence of significant world-wide advances in the development and application of alternative energy sources and increased energy efficiency will exacerbate environmental degradation. Alternative energy sources are being developed but have not made great inroads into worldwide energy production.

The increase in carbon gases in the atmosphere have helped increase the 'greenhouse effect' by which heat radiated from the surface of the Earth is trapped by molecules in the atmosphere. This heat is then radiated back by these molecules, thereby increasing the temperature of Earth's surface. It is thought this will lead to global warming. Nitrogen oxide gases also contribute to the greenhouse effect. In contrast, sulfur dioxide mostly resides in the atmosphere as aerosol droplets that reflect solar energy and thus cool the atmosphere.

Studies of past conditions using gases trapped in glacier ice and isotopic chemistry of ice and of shells precipitated from sea water have helped determine the content of CO₂ in past atmospheres. Direct and proxy temperature records have helped reconstruct ancient climates. From these we are beginning to be able to determine past Earth temperatures. Recent records have also tracked changes in rainfall. An understanding of these patterns and modeling the greenhouse effect permits us to predict future temperature changes and, from them and an understanding of the controls of climate, we are also beginning to predict other climate changes such as rainfall patterns.

One of the consequences of warming is sea level rise. This is due in part to melting ice but also to expansion of the ocean as volume increases with temperature. Rising sea levels lead to erosion of the coastline. This is particularly problematical for areas with heavily built up coastlines, especially where houses and/or hotels have been built right behind the beach.

 What would happen to the world's coastlines if the West Antarctic Ice Sheet melted, raising global sea levels by as much as 20 feet? Some scientists say a collapse is inevitable, possibly even imminent. Click here to get a look at selected coasts in the aftermath of such a melting. You can also have a look at what would be lost if the East Antarctic Ice Sheet were to melt. No one believes this will disintegrate soon. But if it did, it would raise seas around the world by as much as 200 feet. (To play it safe, these images depict a conservative rise of 170 feet.)

• Disruption of soil and release of carbon
• Replacement of vegetation
• Soil exposure for large parts of the year by readying for planting, cultivation, harvesting. Removal of protective cover makes it liable to erosion by water and wind. As agriculture has spread and become increasingly intense it has increased the rate of land erosion to ten times that of the rate in pre-agricultural times.

Since the development of agriculture soil erosion is estimated to have destroyed an area equivalent to a little more than one-third of the present croplands. Construction, urbanization, mining and other such activities are often significant in accelerating the problem of soil removal and thus destruction of agricultural productivity. Nevertheless, the prime causes of soil erosion are deforestation and agriculture. Today the amount agricultural land being lost through soil erosion and other forms of degradation can be put at a minimum of 200,000 km² per year. This site provides data and analysis on land use, soil erosion and soil quality, water quality, wetlands, and other issues regarding the conservation and use of natural resources.

One can estimate the rates of erosion in various ways

• In Colorado Studies of tree rings date time of root exposure. Rates over the last 100 years have been about 1.8 mm per year whereas in previous 300 years rates were between 0.2 and 0.5 mm/year. The six-fold increase in rate has been attributed to the introduction of large numbers of cattle.
• Rates of sedimentation on continental shelves and lake floors can be measured. In the delta of the Yellow River in China rates of sediment accumulation over the last 2,300 years have been ten times higher than those between 10,000 and 2,300 BP
• In the Kuk Swamp in Papua New Guinea there were low rates until 9000 BP. Then came the first phase of forest clearance. Erosion rates increased from 0.15 cm per thousand years to about 1.2 cm per thousand years. In the last few decades , following European contact, extended grasslands, gardens and coffee plantations ® a rate of 34 cm per thousand years.

There has also been erosion by forest removal.

• In the United States the rate of sediment yield per unit area appears to double for every 20% loss in forest cover. Substantial effects due to clear cutting and construction of forest roads. The latter particularly often lead to mass movements such as mudflows, landslides, debris avalanches. Most of this soil eventually finds its way either into reservoirs on the rivers or to the ocean.

Also there are significant effects due to dust storms. The most famous case was the Dust Bowl of the 1930's in central United States. The prime cause was rapid expansion of wheat cultivation in the Great Plains and drought. In 1977 in the San Joaquin valley of CA a dust storm due to drought, very high wind, overgrazing and general lack of windbreaks caused erosion over an area of about 2,000 km². It stripped 25 million metric tons soil from grazing land within a 24 hour period.

Some of China's deforestation problems

- How to transform the eroded red hills of southern China into productive cropland could be the key to managing one of the world's largest scale environmental problems. Because of deforestation, around 480,000 square kilometers of land (an area the size of Spain) across the country's southern region is now considered to be eroded wasteland. In a region that must support 300 million people, heavy storms have left behind acidic red soils that are low in nutrients.

• The increase in sediment due to erosion clogs small streams making drainage less effective and fills reservoirs and lakes. This is particularly an issue when planning large dam projects, such as the Three Gorges Dam on the Yangtze River. One of the purposes of this dam is flood control. Silting would reduce the capacity of the reservoir and thus increase the chance of flooding on cities at the reservoir head.

In order to feed the ever-growing population fertilizers are extensively used in agriculture. Soil and water chemistry has changed due to fertilizer use.

Consequences

• The rise in nutrients starts a chain of events that include a rich growth of algae and other plant life at and near the surface of water bodies. Nutrients are naturally occurring and critical to support plant life in marine ecosystems. But they also contribute to nutrient excess. This in turn leads to an overabundance of phytoplankton. These use up available oxygen and destroy or drive away other marine life. Algal blooms such as red tides that contaminate shellfish, kill fish and coastal wildlife such as manatees, and destroy sea grass and coral reefs.
• At depth get oxygen depletion (hypoxia) due to accumulation of dead organic matter. This oxygen deficiency reduces bottom dwelling life. Problems are particularly bad along the Atlantic coast and Gulf of Mexico. In latter a "dead zone" forms along LA and TX coasts adjacent to the outflows of the Mississippi and Atchafalaya Rivers. This zone rivals those of the Black and Baltic seas. Hypoxia occurs from late February through early October but is most widespread and severe June-August. Evidence suggests increased eutrophication is primarily due to changes in nitrogen content of the rivers.

Nutrients are required by all plant and animal life. Sources of nutrients to streams are both natural and human-derived, and include decaying organic material; fertilizers applied to crops, lawns, and golf courses; manure from fields or feedlots; atmospheric deposition in the form of precipitation or dry deposition; ground-water discharge; and municipal wastewater discharge.

The earliest fertilizers were nitrogen and phosphorous. Much later potassic fertilizers came into use. These have greatly increased agricultural production but have also contaminated surface and ground water and even the atmosphere.

Human activities have more than doubled the amount of N in the environment globally from 1960 to 1990.

• N - comes from atmosphere especially due to burning fossil fuels, mainly from automobile emissions. This is a major contributor to atmospheric pollution. Nitric oxide is a precursor of ground-level ozone, the component of smog that is most dangerous to human health and to crop productivity. It can also be transformed into nitric acid and, together with sulfuric acid resulting from sulfur emissions, be washed out of the atmosphere as acid rain.
• from upstream watersheds due to agricultural runoff (fertilizer and animal waste),
• from waste water treatment.
• more than half of the increase in N is due to synthetic fertilizers. Typically plants take up less than half of the nitrogen applied. The rest is lost into the air, dissolved in surface waters or absorbed into groundwater. In United States about 20% of the N in fertilizers seeps into ground water, rivers, streams and gradually to ocean.

In Chesapeake Bay the Susquehanna accounts for 50% or the fresh water inflow, 70% of the nitrogen load and 60% of the phosphorous.

What has been done to reduce nutrients?

In the Chesapeake Bay Basin the major nutrient control strategies that have been used include the following: (from Chesapeake Bay web page).

• Upgrades to wastewater treatment plants. Municipal and industrial wastewater treatment plants are the principal point sources of nutrients to streams. In response to the Federal Water Pollution Control Act of 1972 and the Water Quality Act of 1987, State and local governments have increasingly supported consolidation of treatment plants and the use of more effective technology in treatment of wastewater, including biological nutrient removal.
• The ban of phosphate detergents. As replacements to phosphorus in detergents were found, detergents containing phosphate were taken off the market. By the late 1980’s, phosphate detergents were banned in all the States that surround Chesapeake Bay.
• The implementation of practices designed to minimize surface runoff of nutrients and suspended material reaching streams from nonpoint sources such as highways, construction sites, farms, and urban areas. Some of these practices, however, can increase nutrient concentrations reaching streams through ground water. This may happened when runoff is diverted away from streams, instead allowing nutrient-rich water to infiltrate to ground water that will eventually discharge to a stream. Because ground water moves slowly, this process may take many years, making the effect difficult to assess. These practices are voluntary for landowners and are not easily monitored.

However there is danger lurking. Three consecutive hydroelectric dams on the Lower Susquehanna form a major reservoir system. Since construction the reservoirs have been filling with sediment and sediment-associated nutrients. The upper two reservoirs have reached their capacity and no longer trap nutrients and sediments. However the lower one, Conowingo Reservoir is currently trapping about 70% of the suspended sediment load, 2% of the nitrogen load and 40% of the phosphorous load that would otherwise be discharged to the Chesapeake Bay. When the reservoirs are all full there will be a 250% average annual increase in the suspended sediment load, a 2% average annual increase in nitrogen and a 70% increase in phosphorus.

Water needs

It is estimated that in 1996 humans used over half the accessible fresh water. Between 1950 and 1990 global water demand tripled and it is still rising. If current trends persist the demand might exceed the total available supply by around 2030. A typical citizen of the US uses about 100 times as much water as a citizen of Uganda.

By far the biggest use for water is agriculture. Between 70 and 80% of the water withdrawn globally is used for irrigation.

6000 years ago settlers in Mesopotamia embarked on new way growing food. They migrated to dry plains between Tigris and Euphrates Rivers (southern Iraq). Crops would sprout and grow but wither from dryness before harvest. Remedy - irrigation. This created food surpluses that had to be stored and distributed which, in turn, led to new forms centralized management and freed many to pursue nonfarm activities. This in turn led to writing, the wheel, sailboats, water-lifting devices, yokes for harnessing animals and cities.

Other early irrigation societies in Nile, Indus of Pakistan and Yellow River, north-central China. This was a new foundation from which civilizations blossomed. But history also tells that the irrigation base requires constant care. Problems include salinization (due to salts carried to the surface that accumulate as the water evaporates), dams canals and levees fall into disrepair, and competition over irrigated land and water.

Irrigation underpins our modern society. It is a key driver in this century's rise in food production. Many nations including China, Egypt, India, Indonesia and Pakistan rely on irrigated land for more than half of their domestic food output. 40% of world food comes from the 17% of cropland that is irrigated. India, China, United States and Pakistan together account for over 1/2 of world's irrigated lands.

After significant growth, irrigated area now diminishing. This is due to the fact that the best and easiest sites already developed. Also there is worsening soil salinization (1/5 of irrigated land is damaged by salt) and shortages of irrigation water. As rivers run dry for parts of year, agriculture is vulnerable to reallocation of water.

A major vulnerability is the depletion of aquifers. Groundwater is being pumped faster than it can be replenished. This leads to a steady drop in water tables. Locally salt water intrusion can occur, especially in coastal areas. This is a wide-spread problem in central, northern China, NW and southern India, parts of Pakistan, much of the western United States, N Africa, Middle East, and the Arabian peninsula.

Example N China. - China is world's largest grain producer, 40% of its grain is produced in the north. Here groundwater over-pumping amounts to 30 billion cubic meters per year. The water table is dropping 1 -1.5 meters a year. How will they respond?

• take land out of irrigated agriculture
• switch to less thirsty crops
• irrigate more efficiently?

Projected 2025 water deficit for the Hai and Yellow River basins is roughly equal to the volume of water needed to grow 55 million tons of grain - 14% of China's current annual grain consumption and more than a quarter of current global grain exports.

China's water use is heavily dominated by irrigation requirements. Nearly half of cropped land is irrigated. But, on a significant share of irrigated land, water is wasted due to the low water charges. The cost of 1000 m³ of water is equivalent to a bottle of mineral water in the market. In Inner Mongolia 6 m³ of water are used per kg of grain, whereas in the Henan province 1 m³ is used to produce the same amount.

Northern China, with only 20 percent of water resources, supports 64 percent of the prime farming land. About 33 percent of China's territory, occupied by 40 percent of its population, receives only about 25 percent of the country's total precipitation. In the North the water for irrigation comes from underground water reserves. In the Loess Plateau the underground water for irrigation is drawn from depths of over 70-100 m, with increasing energy costs.

The excessive water use without adequate drainage leads to waterlogging, salinization and then soil erosion. Salinization and alkalinization affects almost 16 percent of irrigated farmland. In the north-east, cropping activities have increased soil alkalinity to high levels so that their putting back into pasture is difficult. In the sandy soils of the north-west, where the irrigation water seeps away quickly, strong winds and high evaporation contribute to easy alkalization of the soil.

There is also a qualitative aspect of irrigation waters. Water, in general, has been increasingly contaminated by industrial and urban wastes and by leached fertilizers and pesticides.

In the US, by far the most serious is the Ogallala aquifer. This aquifer underlies parts of 8 states and supplies water to 1/5 of United States irrigated land. There is very little replenishment of this aquifer. It is now so costly to pump that many farmers have abandoned irrigated agriculture.

For the area supplied by the Ogallala - Great Plains aquifer:

Area-weighted water-level change in the Great Plains aquifer, in feet.

Like the United States high plains, the Arabian Peninsula and North Africa also rely heavily on fossil aquifers.

The vast majority of fresh water is used to irrigate grain. If so much of irrigated agriculture is operating under water deficits now, where are farmers going to find the additional water needed to feed the more than 2 billion people projected to join humanity's ranks by 2030?

As water becomes more scarce, competition for this resource increases.

• Between cities and industries and agriculture. China had 130 cities in 1949, now 600. Half are already short of water. One cubic meter of water used in China's industries generates more jobs and about 70 times more economic value than the same amount used in agriculture. United States - cities are buying water, water rights, or land that comes with water rights.
• Also there is pressure in many places to return water to the natural environments for fish and wildlife habitat. This is happening in parts of Arizona, California, Colorado, Nevada and elsewhere.
• Between countries. World's hot spots of water dispute:

When a county's renewable water supplies drop below about 1,700 cubic meters per capita it becomes difficult for that country to mobilize enough water to satisfy all the food, household and industrial needs of its population. Countries in this situation typically begin to import grain, reserving their water for household and industrial uses. Each ton of grain represents about 1,000 tons of water. 34 countries in Africa, Asia, Middle East are classified as water-stressed. All but South Africa and Syria are net importers of grain. Collectively these import nearly 1/4 of all grain traded internationally. By 2025 number of people living in water-stressed countries projected to climb from 470 million to 3 billion. This is a > 6 fold increase. Will there be enough grain?

Other consequences of excessive water pumping include significant subsidence of the land and collapse of aquifers that then precludes recharge. In China, the constant and excessive extraction of groundwater has led to the drop in the water table and subsidence. The water table has been reported to drop by 1 to 3 m annually, in some cases as much as 6 m. In Beijing the water table dropped from just 5 m below the surface in the 1950s to around 50 m in the 1980s. The area of subsidence around Beijing is reported to be 1000 km², and that in Tianjin more than 500 km². Around Tianjin in an area of 7000 km² the water table is now 60 m. lower than in the surrounding areas. In the coastal areas of Hebei and Shandong, the excessive drop of groundwater level has led to intrusion of saline water into the freshwater aquifers.

Subsidence in coastal areas is particularly hazardous as it permits salt water intrusion and flooding.

Water will be the major impediment for further development in several regions. Not only is the scarcity of water, together with insufficient arable land, increasingly posing a threat to food self-sufficiency in several regions and forcing a dependence on food trade, but also unsafe water is having a negative impact on human and ecosystem health.

In sum environmental problems, many triggered by human adaptation of the Earth to our needs, result in serious consequences for our future. These problems are more severe in heavily populated and economically challenged countries. Natural processes are interconnected on all scales. "Policy decisions that directly impact civilization today and Earth for generations yet to come too often make the mistake of assuming that we can independently alter or modify one element of a natural system and expect no or few changes elsewhere." (From Palmer, A.R. and Zen, E. - Toward a Stewardship of the Global Commons, Part V. GSA Today - a publication of the Geological Society of America - v. 10, no. 5, p. 10)

Some interesting web sites. Many are the sources of figures on this page.

http://www.climatenews.com/ - Interesting information on climate.

http://earthobservatory.nasa.gov/ - The purpose of NASA's Earth Observatory is to provide a freely-accessible publication on the Internet where the public can obtain new satellite imagery and scientific information about our home planet. The focus is on Earth's climate and environmental change.

http://www.nasm.si.edu/earthtoday/start.htm - A Digital View of our Dynamic Planet

http://www.swcs.org/ - The Soil and water conservation society.

http://grid2.cr.usgs.gov/geo1/ - UN Environment Programme - Global Environment Outlook 1 - 1997

http://grid2.cr.usgs.gov/geo2000/ - UN Environment Programme - Global Environment Outlook 2000

http://webserver.cr.usgs.gov/nawqa/hpgw/HPGW_home.html - US Geological Survey. National Water-Quality Assessment (NAWQA) Program, High Plains Regional Ground Water Study

http://state-of-coast.noaa.gov/

What would happen to the world's coastlines if the West Antarctic Ice Sheet melted, raising global sea levels by as much as 20 feet? Some scientists say a collapse is inevitable, possibly even imminent. Click here to get a look at selected coasts in the aftermath of such a melting. You can also have a look at what would be lost if the East Antarctic Ice Sheet were to melt. No one believes this will disintegrate soon. But if it did, it would raise seas around the world by as much as 200 feet. (To play it safe, these images depict a conservative rise of 170 feet.)

http://www.epa.gov/globalwarming/index.html - The EPA web site on global warming.

http://www.climatehotmap.org/index.html - A map that shows that the Earth is heating up. The early warning signs are in.

Some resources for those interested in reading more about the interactions of humans with the Earth.

• Against the Tide: The Battle for America's Beaches. Cornelia Dean. Columbia University Press, NY (1999) $24.95 ISBN 0231084188
• The Human Impact on the Natural Environment. Andrew Goudie. 5^th edition. MIT Press, MA (2000) $29.95
• Is the Temperature Rising? The Uncertain Science of Global Warming. S. George Philander. Princeton University Press, NJ (1998)
• Planet Under Stress. C. Mungall and D.J. McLaren, Eds. Oxford University Press (1991)