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Monday, November 21, 2022

Environmental impact of concrete

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Environmental_impact_of_concrete

The environmental impact of concrete, its manufacture and applications, are complex, driven in part by direct impacts of construction and infrastructure, as well as by CO₂ emissions; between 4-8% of total global CO₂ emissions come from concrete. Many depend on circumstances. A major component is cement, which has its own environmental and social impacts and contributes largely to those of concrete.

The cement industry is one of the main producers of carbon dioxide, a potent greenhouse gas. Concrete causes damage to the most fertile layer of the earth, the topsoil. Concrete is used to create hard surfaces which contribute to surface runoff that may cause soil erosion, water pollution and flooding. Conversely, concrete is one of the most powerful tools for proper flood control, by means of damming, diversion, and deflection of flood waters, mud flows, and the like. Light-colored concrete can reduce the urban heat island effect, due to its higher albedo. However, original vegetation results in even greater benefit. Concrete dust released by building demolition and natural disasters can be a major source of dangerous air pollution. The presence of some substances in concrete, including useful and unwanted additives, can cause health concerns due to toxicity and (usually naturally occurring) radioactivity. Wet concrete is highly alkaline and should always be handled with proper protective equipment. Concrete recycling is increasing in response to improved environmental awareness, legislation, and economic considerations. Conversely, the use of concrete mitigates the use of alternative building materials such as wood, which is a natural form of carbon sequestering.

Carbon dioxide emissions and climate change

The cement industry is one of the two largest producers of carbon dioxide (CO₂), creating up to 5% of worldwide man-made emissions of this gas, of which 50% is from the chemical process and 40% from burning fuel. The CO₂ produced for the manufacture of structural concrete (using ~14% cement) is estimated at 410 kg/m³ (~180 kg/tonne @ density of 2.3 g/cm³) (reduced to 290 kg/m³ with 30% fly ash replacement of cement). The CO₂ emission from the concrete production is directly proportional to the cement content used in the concrete mix; 900 kg of CO₂ are emitted for the fabrication of every ton of cement, accounting for 88% of the emissions associated with the average concrete mix. Cement manufacture contributes greenhouse gases both directly through the production of carbon dioxide when calcium carbonate is thermally decomposed, producing lime and carbon dioxide, and also through the use of energy, particularly from the combustion of fossil fuels.

One area of the concrete life cycle worth noting is the fact that concrete has a very low embodied energy per unit mass. This is primarily the result of the fact that the materials used in concrete construction, such as aggregates, pozzolans, and water, are relatively plentiful and can often be drawn from local sources. This means that transportation only accounts for 7% of the embodied energy of concrete, while the cement production accounts for 70%. With a total embodied energy of 1.69 GJ/tonne concrete has a lower embodied energy per unit mass than most common building material besides wood. However, concrete structures have high mass, so this comparison is not always directly relevant to decision making. It is worth noting that this value is based on mix proportions for concrete of no more than 20% fly ash. It is estimated that one percent replacement of cement with fly ash represents a 0.7% reduction in energy consumption. With some proposed mixes containing as much as 80% fly ash, this would represent a considerable energy saving.

A 2022 report from the Boston Consulting Group found that, investments in developing greener forms of cement lead to bigger greenhouse gas reductions compared with investments in electricity and aviation.

Mitigation

Design improvements

There is a growing interest in reducing carbon emissions related to concrete from both the academic and industrial sectors, especially with the possibility of future carbon tax implementation. Several approaches to reducing emissions have been suggested.

Cement production and use

One reason why the carbon emissions are so high is because cement has to be heated to very high temperatures in order for clinker to form. A major culprit of this is alite (Ca₃SiO₅), a mineral in concrete that cures within hours of pouring and is therefore responsible for much of its initial strength. However, alite also has to be heated to 1,500 °C in the clinker-forming process. Some research suggests that alite can be replaced by a different mineral, such as belite (Ca₂SiO₄). Belite is also a mineral already used in concrete. It has a roasting temperature of 1,200 °C, which is significantly lower than that of alite. Furthermore, belite is actually stronger once concrete cures. However, belite takes on the order of days or months to set completely, which leaves concrete weak for longer. Current research is focusing on finding possible impurity additives, like magnesium, that might speed up the curing process. It is also worthwhile to consider that belite takes more energy to grind, which may make its full life of impact similar to or even higher than alite.

Another approach has been the partial replacement of conventional clinker with such alternatives as fly ash, bottom ash, and slag, all of which are by-products of other industries that would otherwise end up in landfills. Fly ash and bottom ash come from thermoelectric power plants, while slag is a waste from blast furnaces in the ironworks industry. These materials are slowly gaining popularity as additives, especially since they can potentially increase strength, decrease density, and prolong durability of concrete.

The main obstacle to wider implementation of fly ash and slag may be largely due to the risk of construction with new technology that has not been exposed to long field testing. Until a carbon tax is implemented, companies are unwilling to take the chance with new concrete mix recipes even if this reduces carbon emissions. However, there are some examples of "green" concrete and its implementation. One instance is a concrete company called Ceratech that has started manufacturing concrete with 95% fly ash and 5% liquid additives. Another is the I-35W Saint Anthony Falls Bridge, which was constructed with a novel mixture of concrete that included different compositions of Portland cement, fly ash, and slag depending on the portion of the bridge and its material properties requirements.

Furthermore, the production of concrete requires large amounts of water, and global production accounts for almost a tenth of worldwide industrial water use. This amounts to 1.7 percent of total global water withdrawal. A study that appeared in Nature Sustainability in 2018 predicts that concrete production will in the future increase pressure on water resources in regions susceptible to drought conditions: "In 2050, 75% of the water demand for concrete production will likely occur in regions that are expected to experience water stress."

Carbon concrete

Carbonatation in concrete is the formation of calcium carbonate (CaCO₃) by chemical reaction. The speed of carbonation depends primarily on the porosity of the concrete and the moisture content. Carbonation in concrete pores happens only at a relative humidity (RH) of 40-90%, when RH is higher than 90% carbon dioxide cannot enter the concrete pores, and also when RH is lower than 40% CO₂ cannot be dissolved in water

Pore structures in fresh concrete and air entrained concrete

Concrete can be subjected for the most part by two types of carbonation: weathering carbonation and early age carbonation.

Weathering carbonation, occurs in concrete when calcium compounds react with carbon dioxide CO₂ from the atmosphere and water $H_{2}^{} O$ in the concrete pores. The reaction is as follows:

First, through chemical weathering CO₂ reacts with water in the concrete pores to form carbonic acid:

{CO}_{2}^{} + H_{2}^{} O \overset{- ⇀}{↽ -} H_{2}^{} {CO}_{3}^{}

carbon dioxide + water → carbonic acid

Carbonic acid then reacts with calcium carbonate:

Ca(OH)₂ + H₂CO₃ → CaCO₃ + 2H₂O

carbonic acid + calcium carbonate → calcium bicarbonate

Third Once the calcium hydroxide (Ca(OH)₂) has carbonated, the main component of Cement calcium silicate hydrate gel (also shown as C-S-H) can be decalcified, allowing the liberated CaO to carbonate:

H₂CO₃ + CaO → CaCO₃ + H₂O

Early age carbonation is when we introduce CO₂ to the early stages of fresh premix concrete or upon initial curing, it can be both natural through exposure or accelerated by augmenting a direct intake of CO₂. Gaseous carbon dioxide is converted to solid carbonates and can be permanently stored in concrete for emission reduction, the general reaction of CO₂ and calcium silicate hydrate in cement was described in 1974 as:

C3S + 3 CO₂ + H₂O → C-S-H + 3CaCO₃ + 347 kJ/mol

C2S + 2 CO₂ + H₂O → C-S-H + 2CaCO₃ + 184 KJ/mol

A Canadian company patented and commercialized a novel technology that uses the early age type of carbonation to sequester CO₂. This is achieved by directly injecting recycled liquid carbon dioxide from third party industrial emitters, into the concrete wet mix stage during the manufacturing process. Whereby a chemical reaction CO₂ becomes a mineral, sequestering the greenhouse gas pollutant in concrete infrastructures, buildings, roads, etc for long periods of time. Moreover in a study published in the journal of Cleaner Production authors performed a model where they proved that CO₂ improved the compressive strength of the concrete while reducing CO₂ emissions as a result, in so allowing for a cement loading reduction while at the same time having a "4.6% reduction in the carbon footprint."

Another proposed method of capturing emissions is to absorb CO₂ in the curing process, by the use of an admixture (a dicalcium silicate y phase) as the concrete cures. The use of coal ash or another suitable substitute, could theoretically have CO₂ emissions below 0 kg/m³, compared to portland cement concrete at 400 kg/m³. The most effective method of production of this concrete would use the exhaust gas of a power plant, where an isolated chamber could control temperature and humidity.

In August 2019, reduced CO₂ cement was announced which "reduces the overall carbon footprint in precast concrete by 70%.". The base of these cement being primarily of wollastonite (Ca Si O₃) and rankinite (3CaO·2SiO₂) in contrast to traditional Portland cement alite (3CaO·SiO₂) belite (2 CaO · SiO₂).

The patented process of concrete making begins with the bonding of particles through liquid phase sintering also referred to as hydrothermal liquid phase densification (rHLPD). A solution mixed of H
₂O and CO₂ penetrates the particles, in reaction with ambient conditions to create a bond which creates the reduced-lime, non-hydraulic calcium silicate cement (CSC). Moreover the difference between traditional portland concrete and these carbonated calcium silicate concrete (CSC-C) lies in the final curing process reaction between a water-CO₂ solution and a family of calcium-silicate: "CSC-C curing is a mildly exothermic reaction in which the low-lime calcium silicates in the CSC react with carbon dioxide in the presence of water to produce calcite (CaCO₃) and silica (SiO₂) as shown in Reactions II and III. II. CaO.SiO₂ + CO₂ → H₂O CaCO₃ + SiO₂

III: 3CaO.2SiO₂ + 3CO₂ → H₂O 3CaCO₃ + 2SiO₂" However as early age carbonation methods have gained recognition due to its substantial carbon sequestration proficiencies, some authors argue the effect of early-age carbonation curing under weathering carbonation for precast concrete "Experimental results suggest that early-age carbonated concretes with high w/c ratios (>0.65>0.65) are more likely to be affected by weathering carbonation", and advise this may weaken its strength abilities in the corrosion stages during life service.

Italian company Italcementi designed a kind of cement that is supposedly alleviating air pollution by breaking down pollutants that come in contact with the concrete, through the use of titanium dioxide absorbing ultraviolet light. Some environmental experts nevertheless remain skeptical and wonder if the special material can 'eat' enough pollutants to make it financially viable. Jubilee Church in Rome is built from this kind of concrete.

Another aspect to consider in carbon concrete is surface scaling due to cold climatic conditions and exposure to de-icing salt and freeze-thaw cycle (frost weathering). Concrete produced by carbonation curing also shows superior performance when subject to physical degradations, e.g., freeze-thaw damage, particularly due to the pore densification effect enabled by the precipitation of carbonation products.

Some studies link a reduction of CO₂ to concrete production, but they are mostly written by authors associated with the proposed solution or the concrete industry. This should give concern that these solutions are greenwashing. The CO₂ emissions from concrete come from the cement in the mixture, methods to reduce the amount of the cement are the only proven methods to reduce the emissions.

Photocatalysis to reduce smog

TiO₂, a semiconductor material shown to exhibit photocatalytic behavior, has been used to remove NOx from the atmosphere. NO_x species, or nitrogen oxide and nitrogen dioxide (x = 1 and 2 respectively), are atmospheric gases that contribute to acid rain and smog formation, both of which are the result of urban pollution. Since NO_x formation only occurs at high temperatures, nitrogen oxides are typically produced as a byproduct of hydrocarbon combustion. In addition to contributing to urban pollution events, NO_x has also been demonstrated to cause a wide variety of adverse health and environmental effects; these effects include triggering respiratory distress, reacting with other atmospheric chemicals to form harmful products such as ozone, nitroarenes, and nitrate radicals, and contributing to the greenhouse effect. The World Health Organization (WHO) has recommended a maximum NO_x concentration of 40ug/m³. One proposed route of decreasing NO_x concentrations, especially in urban settings is to use a photocatalytic TiO₂ mixed into concrete to oxidize NO and NO₂ to form nitrate. In the presence of light, TiO₂ generates electrons and holes that allows for NO to oxidize into NO₂ and NO₂ to then form HNO₃ via a hydroxyl radical attack. Molecule adsorption:

O₂ + site → O_ads

H₂O + site → H₂O_ads

NO + site → NO_ads

NO₂ + site → NO_2ads

Generation of holes and electrons via TiO₂ activation:

TiO₂ + hν → e⁻ + h⁺

Trapping of electron/hole:

h⁺ + H₂O_ads → OH· + H⁺

e⁻ + O_2ads → O₂⁻

Hydroxyl radical attack:

NO_ads + OH· → HNO₂

HNO₂ + OH· → NO_2ads + H₂O

NO_2ads + OH· → NO₃⁻ + H⁺

Electron and hole recombination:

e⁻ + h⁺ → heat

Another pathway for the oxidation of nitrogen uses UV irradiation to form NO₃.

Embedded solar cells

Dye-sensitized solar cells embedded in concrete has been proposed as a method of reducing the carbon and energy footprints of buildings. The usage of embedded solar cells allows for on-site energy generation, which when coupled with batteries, would provide constant power throughout the day. The top layer of the concrete would be a thin layer of dye-sensitized solar cells. Dye-sensitized solar cells are particularly attractive due to its ease of mass production, either via roll-printing or painting, and a reasonably high efficiency of 10%. One example of the commercialization of this concept is the German company Discrete, which produces a dye-sensitized solar cell embedded concrete product. Their process uses a spray-coating method to apply organic dyes that generate electricity onto concrete.

Energy storage

Energy storage has become an important consideration for many renewable energy generation methods, especially for popular methods such as solar or wind energy, both of which are intermittent energy producers that require storage for constant use. Currently, 96% of the world’s energy storage comes from pumped hydro, which uses excess generated electricity to pump water up a dam and then allowed to fall and turn turbines that produce electricity when the demand exceeds generation. The problem with pumped hydro, however, is that the setup requires specific geographies that can be difficult to find. A similar concept that uses cement instead of water has been realized by Energy Vault, a Swiss startup. They created a setup that uses an electric crane surrounded by stacks of 35-ton concrete blocks, which can be produced using waste products, to store energy by using excess energy generation to power the crane to lift and stack the concrete blocks. When energy is needed, the blocks are allowed to fall and the rotated motor would send energy back to the grid. The setup would have a storage capacity of 25-80 MWh.

Other improvements

There are many other improvements to concrete that do not deal directly with emissions. Recently, much research has gone into "smart" concretes: concretes that use electrical and mechanical signals to respond to changes in loading conditions. One variety uses carbon fiber reinforcement which provides an electrical response that can be used to measure strain. This allows for monitoring the structural integrity of the concrete without installing sensors.

The road construction and maintenance industry consumes tons of carbon-intensive concrete every day to secure road-side and urban infrastructure. As populations grow this infrastructure is becoming increasingly vulnerable to impact from vehicles, creating an ever increasing cycle of damage and waste and ever increasing consumption of concrete for repairs (roadworks are now seen around our cities on almost a daily basis). A major development in the infrastructure industry involves the use of recycled petroleum waste to protect the concrete from damage and enable infrastructure to become dynamic, able to be easily maintained and updated without disturbance to the existing foundations. This simple innovation preserves the foundations for the entire lifespan of a development.

Another area of concrete research involves the creation of certain “waterless” concretes for use in extraplanetary colonization. Most commonly, these concretes use sulfur to act as a non-reactive binder, allowing for construction of concrete structures in environments with no or very little water. These concretes are in many ways in distinguishable from normal hydraulic concrete: they have similar densities, can be used with currently existing metal reinforcement, and they actually gain strength faster than normal concrete This application has yet to be explored on Earth, but with concrete production representing as much as two-thirds of the total energy usage of some developing countries, any improvement is worth considering.

Changes in use

Concrete is one of the world's oldest man-made building materials. Over the years, significant environmental limitations have been placed on the creation and use of concrete due to its carbon footprint. Manufacturers responded to these limitations by altering concrete's production processes, and recycling old concrete rubble to use as aggregate in new concrete mixtures to reduce these emissions. Concrete has immersed from natural resources into man-made processes; evidence of the use of concrete dates back over 8,000 years ago. Today, many construction companies and concrete manufacturers have cut the use of Portland cement in their mixtures due to its production process emitting significant amounts of greenhouse gases into the atmosphere.

Alternatives to concrete

There are in fact many alternatives to concrete. One being Green concrete that is produced by recycled waste materials from various industries , another being Ashcrete, a material made from a mix of lime and water that acts similar to cement. Black furnace slag is also a strong alternative made from molten iron slag into water, along with Micro Silica, Papercrete, composite cement, and post-consumer glass.

Depending on the amounts required or used overall and the amounts needed, in combination with other materials, for structural stability per building, many other materials also have a substantial negative impact on the environment. For instance, while research and development to reduce these emissions are ongoing, steel accounted for ~8 % of the world's total greenhouse gas emissions as of 2021.

Clay

The Tecla eco-house as of 2021

Mixtures of clay are an alternative construction material to concrete that have a lower environmental footprint. In 2021, the first prototype 3D printed house, Tecla, printed from locally-sourced soil and water as well as fibers from rice husks and a binder was completed. Such buildings could be very inexpensive, well-insulated, stable and weatherproof, climate-adaptable, customizable, get produced rapidly, require only very little easily-learnable manual labor, require less energy, produce very little waste and reduce carbon emissions from concrete.

Surface runoff

Surface runoff, when water runs off impervious surfaces, such as non-porous concrete, can cause severe soil erosion and flooding. Urban runoff tends to pick up gasoline, motor oil, heavy metals, trash and other pollutants from sidewalks, roadways and parking lots. Without attenuation, the impervious cover in a typical urban area limits groundwater percolation and causes five times the amount of runoff generated by a typical woodland of the same size. A 2008 report by the United States National Research Council identified urban runoff as a leading source of water quality problems.

In an attempt to counteract the negative effects of impervious concrete, many new paving projects have begun to use pervious concrete, which provides a level of automatic stormwater management. Pervious concrete is created by careful laying of concrete with specifically designed aggregate proportions, which allows for surface runoff to seep through and return to the groundwater. This both prevents flooding and contributes to groundwater replenishment. If designed and layered properly, pervious concrete and other discreetly paved areas can also function as an automatic water filter by preventing certain harmful substances like oils and other chemicals from passing through. Unfortunately there are still downsides to large scale applications of pervious concrete: its reduced strength relative to conventional concrete limits use to low-load areas, and it must be laid properly to reduce susceptibility to freeze-thaw damage and sediment buildup.

Urban heat

Both concrete and asphalt are the primary contributors to what is known as the urban heat island effect. According to the United Nations Department of Economic and Social Affairs 55% of the world’s population reside in urban areas and 68% of the world’s population is projected to be urban by 2050; also, "the world is projected to add 230 billion m2 (2.5 trillion ft2) of buildings by 2060, or an area equal to the entire current global building stock. This is the equivalent of adding an entire New York City to the planet every 34 days for the next 40 years". As a result, paved surfaces represent a major concern because of the additional energy consumption and air pollution they cause.

The potential of energy saving within an area is also high. With lower temperatures, the demand for air conditioning theoretically decreases, saving energy. However, research into the interaction between reflective pavements and buildings has found that, unless the nearby buildings are fitted with reflective glass, solar radiation reflected off pavements can increase building temperatures, increasing air conditioning demands.

Moreover, heat transfer from pavements, which cover about one-third of a typical U.S. city, can also influence local temperatures and air quality. Hot surfaces warm the city air through convection, so using materials that absorb less solar energy, such as high-albedo pavements, can reduce the flow of heat into the urban environment and moderate the UHIE. Albedos range from about 0.05 to about 0.35 for currently used pavement material surfaces. Over a typical life service, pavement materials that begin with high albedo tend to lose reflectance, while those with low initial albedo may gain reflectance

The Design Trust for Public Space found that by slightly raising the albedo value in New York City, beneficial effects such as energy savings could be achieved., by replacement of black asphalt with light-colored concrete. However, in winter this may be a disadvantage as ice will form more easily and remain longer on light colored surfaces as they will be colder due to less energy absorbed from the reduced amount of sunlight in winter.

Another aspect to consider is thermal comfort effect, as well as the need for more mitigation strategies, which don’t threat the health and wellbeing of pedestrians particularly during heat waves. A study that appeared in Building and Environment in 2019 performed experiments to project the impact of heat waves and high albedo materials interactions in the northern Italian city of Milan. By calculating the "Mediterranean Outdoor Comfort Index" (MOCI) in presence of a heat wave, where high albedo materials was used in all surfaces. The study identified a deterioration of the microclimate where high amounts of high albedo materials were located. The use of the high albedo materials was found to "lead to the establishment of multiple inter-reflections and a consequent increase in micrometeorological variables such as average radiant temperatures and air temperatures. To be more detailed, these changes lead to an increase in the MOCI that in the afternoon hours can even reach 0.45 units".

Overall urban configurations should remain of concern when making decisions as people are exposed to weather and thermal confort conditions. The use of high albedo materials within an urban environment can be of positive effect with proper combination of other technologies and strategies such as: vegetation, reflective materials, etc. Urban heat mitigation measures could minimize impacts on microclimate as well as human and wildlife habitats.

Concrete dust

Building demolition and natural disasters such as earthquakes often release a large amount of concrete dust into the local atmosphere. Concrete dust was concluded to be the major source of dangerous air pollution following the Great Hanshin earthquake.

Toxic and radioactive contamination

The presence of some substances in concrete, including useful and unwanted additives, can cause health concerns. Natural radioactive elements (K, U, Th, and Rn) can be present in various concentration in concrete dwellings, depending on the source of the raw materials used. For example, some stones naturally emit Radon, and Uranium was once common in mine refuse. Toxic substances may also be unintentionally used as the result of contamination from a nuclear accident. Dust from rubble or broken concrete upon demolition or crumbling may cause serious health concerns depending also on what had been incorporated in the concrete. However, embedding harmful materials in concrete is not always dangerous and may in fact be beneficial. In some cases, incorporating certain compounds such as metals in the hydration process of cement immobilizes them in a harmless state and prevents them from being released freely elsewhere.

Handling precautions

Handling of wet concrete must always be done with proper protective equipment. Contact with wet concrete can cause skin chemical burns due to the caustic nature of the mixture of cement and water. Indeed, the pH of fresh cement water is highly alkaline due to the presence of free potassium and sodium hydroxides in solution (pH ~ 13.5). Eyes, hands and feet must be correctly protected to avoid any direct contact with wet concrete and washed without delay if necessary.

Concrete recycling

Recycled crushed concrete being loaded into a semi-dump truck to be used as granular fill

Concrete recycling is an increasingly common method of disposing of concrete structures. Concrete debris was once routinely shipped to landfills for disposal, but recycling is increasing due to improved environmental awareness, governmental laws and economic benefits.

Concrete, which must be free of trash, wood, paper and other such materials, is collected from demolition sites and put through a crushing machine, often along with asphalt, bricks and rocks.

Reinforced concrete contains rebar and other metallic reinforcements, which are removed with magnets and recycled elsewhere. The remaining aggregate chunks are sorted by size. Larger chunks may go through the crusher again. Smaller pieces of concrete are used as gravel for new construction projects. Aggregate base gravel is laid down as the lowest layer in a road, with fresh concrete or asphalt placed over it. Crushed recycled concrete can sometimes be used as the dry aggregate for brand new concrete if it is free of contaminants, though the use of recycled concrete limits strength and is not allowed in many jurisdictions. On 3 March 1983, a government-funded research team (the VIRL research.codep) approximated that almost 17% of worldwide landfill was by-products of concrete-based waste.

Environmental issues in the United States

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Environmental_issues_in_the_United_States

Of the major greenhouse gas emitting nations, the U.S. is among the highest per person emitters.

Annual CO₂ emissions, total by country (2017 data) shows the U.S. trails China in total annual emissions (not per capita.

Environmental issues in the United States include climate change, energy, species conservation, invasive species, deforestation, mining, nuclear accidents, pesticides, pollution, waste and over-population. Despite taking hundreds of measures, the rate of environmental issues is increasing rapidly instead of reducing. The United States is among the most significant emitters of greenhouse gasses in the world. In terms of both total and per capita emissions, it is among the largest contributors. The climate policy of the United States has big influence on the world.

Movements and ideas

20th century

Both conservationism and environmentalism appeared in political debate in forests about the Progressive Era in the early 20th century. There were three main positions. The laissez-faire position held that owners of private property—including lumber and mining companies, should be allowed to do anything they wished for their property.

The Conservationists, led by President Theodore Roosevelt and his close ally Gifford Pinchot, said that the laissez-faire approach was too wasteful and inefficient. In any case, they noted, most of the natural resources in the western states were already owned by the federal government. The best course of action, they argued, was a long-term plan devised by national experts to maximize the long-term economic benefits of natural resources.

Environmentalism was the third position, led by John Muir (1838–1914). Muir's passion for nature made him the most influential American environmentalist. Muir preached that nature was sacred and humans are intruders who should look but not develop. He founded the Sierra Club and remains an icon of the environmentalist movement. He was primarily responsible for defining the environmentalist position, in the debate between Conservation and environmentalism.

Environmentalism preached that nature was almost sacred, and that man was an intruder. It allowed for limited tourism (such as hiking), but opposed automobiles in national parks. It strenuously opposed timber cutting on most public lands, and vehemently denounced the dams that Roosevelt supported for water supplies, electricity and flood control. Especially controversial was the Hetch Hetchy dam in Yosemite National Park, which Roosevelt approved, and which supplies the water supply of San Francisco.

Climate change

Geographic extent of warming: Average temperatures in almost all regions in the U.S. have increased in the last 120 years.

Warming over time: Annual temperatures averaged across the U.S. have exceeded the 1971–2000 average almost every year in the 21st century.

Climate change in the United States has led to the country warming by 2.6 °F (1.4 °C) since 1970. Due to climate change, the climate of the United States is shifting in ways that are widespread and varied between regions. From 2010 to 2019, the United States experienced its hottest decade on record. Extreme weather events, invasive species, floods and droughts are increasing. Climate change's impacts on tropical cyclones and sea level rise also affects regions of the country.

Cumulatively since 1850, the U.S. has emitted a larger share than any country of the greenhouse gases causing current climate change, with some 20% of the global total of carbon dioxide alone. Current US emissions per person are among the largest in the world. Various state and federal climate change policies have been introduced, and the US has ratified the Paris Agreement despite temporarily withdrawing. In 2021, the country set a target of halving its annual greenhouse gas emissions by 2030.

Climate change is having considerable impacts on the environment and society of the United States. This includes implications for agriculture, the economy, human health and indigenous peoples, and it is seen as a national security threat. States that emit more carbon dioxide per person and introduce policies to oppose climate action are generally experiencing greater impacts. 2020 was a historic year for billion-dollar weather and climate disasters in U.S.

Although historically a non-partisan issue, climate change has become controversial and politically divisive in the country in recent decades. Oil companies have known since the 1970s that burning oil and gas could cause global warming but nevertheless funded deniers for years. Despite the support of a clear scientific consensus, as of 2021 one third of Americans deny that human-caused climate change exists although the majority are concerned or alarmed about the issue.

NOAA's National Centers for Environmental Information (NCEI) has reported growing numbers of weather and climate-related events costing at least a billion dollars, exceeding the 1980–2019 inflation-adjusted average of 6.6 such events.

Energy

Since about 26% of all types of energy used in the United States are derived from fossil fuel consumption it is closely linked to greenhouse gas emissions. The energy policy of the United States is determined by federal, state and local public entities, which address issues of energy production, distribution, and consumption, such as building codes and gas mileage advancements. The production and transport of fossil fuels are also tied to significant environmental issues.

Species conservation

Many plant and animal species became extinct in North America soon after first human arrival, including the North American megafauna; others have become nearly extinct since European settlement, among them the American bison and California condor.

The last of the passenger pigeons died in 1914 after being the most common bird in North America. They were killed as both a source of food and because they were a threat to farming. Saving the bald eagle, the national bird of the U.S., from extinction was a notable conservation success.

As of 13 December 2016, the International Union for the Conservation of Nature's Red List shows the United States has 1,514 species on its threatened list (critically endangered, endangered and vulnerable categories).

Invasive species

The brown tree snake (Boiga irregularis), an invasive species in the United States.

Invasive species are a significant threat to many native habitats and species of the United States and a significant cost to agriculture, forestry, and recreation. The term "invasive species" can refer to introduced/naturalized species, feral species, or introduced diseases. Some introduced species, such as the dandelion, do not cause significant economic or ecologic damage and are not widely considered as invasive. Economic damages associated with invasive species' effects and control costs are estimated at $120 billion per year.

Kudzu, a Japanese vine species invasive in the southeast United States, growing in Atlanta, Georgia

Deforestation

Virgin forest in the U.S.

In 1620

In 1850

In 1926

Deforestation in the United States was an ongoing process until recently. Between 2010 and 2020, the US forests increased 0.03% annually, according to FAO (Food and Agriculture Organization of the United Nations).

Native Americans cleared millions of acres of forest for many reasons, including hunting, farming, berry production, and building materials. Prior to the arrival of European-Americans, about one half of the United States land area was forest, about 1,023,000,000 acres (4,140,000 km²) estimated in 1630. Forest cover in the Eastern United States reached its lowest point in roughly 1872 with about 48 percent compared to the amount of forest cover in 1620. The majority of deforestation took place prior to 1910 with the Forest Service reporting the minimum forestation as 721,000,000 acres (2,920,000 km²) around 1920. The forest resources of the United States remained relatively constant through the 20th century. The Forest Service reported total forestation as 766,000,000 acres (3,100,000 km²) in 2012. A 2017 study estimated 3 percent loss of forest between 1992 and 2001.

The 2005 (FAO) Global Forest Resources Assessment ranked the United States as seventh highest country losing its old growth forests, a vast majority of which were removed prior to the 20th century.

Mining

Mining in the United States has been active since the beginning of colonial times, but became a major industry in the 19th century with a number of new mineral discoveries causing a series of mining rushes. In 2015, the value of coal, metals, and industrial minerals mined in the United States was US $109.6 billion. 158,000 workers were directly employed by the mining industry.

The mining industry has a number of impacts on communities, individuals and the environment. Mine safety incidents have been important parts of American occupational safety and health history. Mining has a number of environmental impacts. In the United States, issues like mountaintop removal, and acid mine drainage have widespread impacts on all parts of the environment. As of January 2020. the EPA lists 142 mines in the Superfund program.

In 2019, the country was the 4th world producer of gold; 5th largest world producer of copper; 5th worldwide producer of platinum; 10th worldwide producer of silver; 2nd largest world producer of rhenium; 2nd largest world producer of sulfur; 3rd largest world producer of phosphate; 3rd largest world producer of molybdenum; 4th largest world producer of lead; 4th largest world producer of zinc; 5th worldwide producer of vanadium; 9th largest world producer of iron ore; 9th largest world producer of potash; 12th largest world producer of cobalt; 13th largest world producer of titanium; world's largest producer of gypsum; 2nd largest world producer of kyanite; 2nd largest world producer of limestone; in addition to being the 2nd largest world producer of salt. It was the world's 10th largest producer of uranium in 2018.

Abandoned fossil fuel wells

Abandoned gas well pump

Though different jurisdictions have varying criteria for what exactly qualifies as an orphaned or abandoned oil well, generally speaking, an oil well is considered abandoned when it has been permanently taken out of production. Similarly, orphaned wells may have different legal definitions across different jurisdictions, but can be thought of as wells whose legal owner it is not possible to determine.

Once a well is abandoned, it can be a source of toxic emissions and pollution contaminating groundwater and releases methane, making orphan wells a significant contributor to national greenhouse gas emissions. For this reason, several state and federal programs have been initiated to plug wells; however, many of these programs are under capacity. In states like Texas and New Mexico, these programs do not have enough funding or staff to fully evaluate and implement mitigation programs.

North Dakota dedicated $66 million of its CARES Act pandemic relief funds for plugging and reclaiming abandoned and orphaned wells.

According to the Government Accountability Office, the 2.1 million unplugged abandoned wells in the United States could cost as much as $300 billion. A joint Grist and The Texas Observer investigation in 2021 highlighted how government estimates of abandoned wells in Texas and New Mexico were likely underestimated and that market forces might have reduced prices so much creating peak oil conditions that would lead to more abandonment. Advocates of programs like the Green New Deal and broader climate change mitigation policy in the United States have advocated for funding plugging programs that would address stranded assets and provide a Just Transition for skilled oil and gas workers.

The REGROW Act, which is part of the Infrastructure Investment and Jobs Act, includes $4.7 billion in funds for plugging and maintaining orphaned wells. The Interior Department has documented the existence of 130,000 orphaned wells nationwide. An EPA study estimated that there are as many as two to three million wells across the nation. New York State is expecting to receive $70 million from the Act in 2022 which will be used to plug orphaned wells. The state has 6,809 orphaned wells, and the NYSDEC estimates it will cost $248 million to plug them all. The NYSDEC uses a fleet of drones carrying magnetometers to find orphaned wells.

Nuclear

The locations across the U.S. where nuclear waste is stored

The most notable accident involving nuclear power in the United States was Three Mile Island accident in 1979. Davis-Besse Nuclear Power Station has been the source of two of the top five most dangerous nuclear incidents in the United States since 1979.

Nuclear safety in the United States is governed by federal regulations and continues to be studied by the Nuclear Regulatory Commission (NRC). The safety of nuclear plants and materials controlled by the U.S. government for research and weapons production, as well those powering naval vessels, is not governed by the NRC.

The anti-nuclear movement in the United States consists of more than eighty anti-nuclear groups which have acted to oppose nuclear power and/or nuclear weapons in the USA. The movement has delayed construction or halted commitments to build some new nuclear plants, and has pressured the Nuclear Regulatory Commission to enforce and strengthen the safety regulations for nuclear power plants. Anti-nuclear campaigns that captured national public attention in the 1970s and 1980s involved the Calvert Cliffs Nuclear Power Plant, Seabrook Station Nuclear Power Plant, Diablo Canyon Power Plant, Shoreham Nuclear Power Plant, and Three Mile Island.

Pesticides

Pesticide use in the United States is predominately by the agricultural sector, which in 2012 comprised 89% of conventional pesticide usage in the United States.

The Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) was first passed in 1947, giving the United States Department of Agriculture responsibility for regulating pesticides. In 1972, FIFRA underwent a major revision and transferred responsibility of pesticide regulation to the Environmental Protection Agency and shifted emphasis to protection of the environment and public health.

Pollution

Pollution from the Exxon Valdez oil spill.

As with many countries, pollution in the United States is a concern for environmental organizations, government agencies and individuals.

Pollution from U.S. manufacturing has declined massively since 1990 (despite an increase in production). A 2018 study in the American Economic Review found that environmental regulation is the primary driver of the reduction in pollution.

Air pollution

Looking down from the Hollywood Hills, with Griffith Observatory on the hill in the foreground, air pollution is visible in downtown Los Angeles on a late afternoon.

Air pollution is the introduction of chemicals, particulate matter, or biological materials into the atmosphere, causing harm or discomfort to humans or other living organisms, or damaging ecosystems. Air pollution can cause health problems including, but not limited to, infections, behavioral changes, cancer, organ failure, and premature death. These health effects are not equally distributed across the U.S population; there are demographic disparities by race, ethnicity, socioeconomic status, and education. Air pollution has affected the United States since the beginning of the Industrial Revolution.

According to a 2009 report, around "60 percent of Americans live in areas where air pollution has reached unhealthy levels that can make people sick." Analyzing data from 2016–2018, the American Lung Association found major declines in air quality, including increases in ground-level ozone.

In 2016, a study found that levels of nitrogen oxides had plummeted over the previous decade, due to better regulations, economic shifts, and technological innovations. NASA reported a 32% decrease of nitrogen dioxide in New York City and a 42% decrease in Atlanta between the periods of 2005–2007 and 2009–2011.

Water pollution

Topsoil runoff from farm, central Iowa (2011).

Water pollution in the United States is a growing problem that became critical in the 19th century with the development of mechanized agriculture, mining, and industry, although laws and regulations introduced in the late 20th century have improved water quality in many water bodies. Extensive industrialization and rapid urban growth exacerbated water pollution as a lack of regulation allowed for discharges of sewage, toxic chemicals, nutrients and other pollutants into surface water.

In the early 20th century, communities began to install drinking water treatment systems, but control of the principal pollution sources—domestic sewage, industry, and agriculture—was not effectively addressed in the US until the later 20th century. These pollution sources can affect both groundwater and surface water. Multiple pollution incidents such as the Kingston Fossil Plant coal fly ash slurry spill (2008) and the Deepwater Horizon oil spill (2010) have left lasting impacts on water quality, ecosystems, and public health in the United States.

Many solutions to water pollution in the United States can be implemented to curtail water pollution. This includes municipal wastewater treatment, agricultural and industrial wastewater treatment, erosion and sediment control, and the control of urban runoff. The continued implementation of pollution prevention, control and treatment measures are used to pursue the goal of maintaining water quality within levels specified in federal and state regulations. However, many water bodies across the country continue to violate water quality standards in the 21st century.

Marine pollution

Plastic pollution

The United States is the biggest creator of plastic waste and the third largest source of ocean plastic pollution, e.g. plastic waste that gets into the oceans. Much of the plastic waste generated in the United States is shipped to other countries.

Solid waste

At 760 kg per person the United States generates the greatest amount of municipal waste. In 2018 municipal waste totaled 292.4 million short tons (265.3×10⁶ t), or 4.9 pounds (2.2 kg) per person per day.

Policy

Solid waste policy in the United States is aimed at developing and implementing proper mechanisms to effectively manage solid waste. For solid waste policy to be effective, inputs should come from stakeholders, including citizens, businesses, community-based organizations, non-governmental organizations, government agencies, universities, and other research organizations. These inputs form the basis of policy frameworks that influence solid waste management decisions. In the United States, the Environmental Protection Agency (EPA) regulates household, industrial, manufacturing, and commercial solid and hazardous wastes under the 1976 Resource Conservation and Recovery Act (RCRA). Effective solid waste management is a cooperative effort involving federal, state, regional, and local entities. Thus, the RCRA's Solid Waste program section D encourages the environmental departments of each state to develop comprehensive plans to manage nonhazardous industrial and municipal solid waste.

Electronic waste

Cathode ray tube monitors being packed for shipping.

Electronic waste or e-waste in the United States refers to electronic products that have reached the end of their operable lives, and the United States is beginning to address its waste problems with regulations at a state and federal level. Used electronics are the quickest-growing source of waste and can have serious health impacts. The United States is the world leader in producing the most e-waste, followed closely by China; both countries domestically recycle and export e-waste. Only recently has the United States begun to make an effort to start regulating where e-waste goes and how it is disposed of. There is also an economic factor that has an effect on where and how e-waste is disposed of. Electronics are the primary users of precious and special metals, retrieving those metals from electronics can be viewed as important as raw metals may become more scarce

The United States does not have an official federal e-waste regulation system, yet certain states have implemented state regulatory systems. The National Strategy for Electronic Stewardship was co-founded by the Environmental Protection Agency (EPA), the Council on Environmental Quality (CEQ), and the General Services Administration (GSA), and was introduced in 2011 to focus on federal action to establish electronic stewardship in the United States. E-waste management is critical due to the toxic chemicals present in electronic devices. According to the United States EPA, toxic substances such as lead, mercury, arsenic, and cadmium are often released into the environment and endanger whole communities; these toxic contaminants can have detrimental effects on the health of ecosystems and living organisms. United States e-waste management includes recycling and reuse programs, domestic landfill dumping, and international shipments of domestically produced e-waste. The EPA estimates that in 2009, the United States disposed of 2.37 million tons of e-waste, 25% of which was recycled domestically.

Lack of awareness for e-waste issues is also a problem in the U.S., especially among young people. In a 2020 survey of people between the ages of 18 and 38, 60% did not know what the term "e-waste" is, and 57% did not consider electronic waste to be "a significant contributor to toxic waste." With electronic recycling options readily available in most states, the issue seems to be awareness, not availability. In 2018, an association of European electronic recyclers based in Brussels called the WEEE Forum, created International E-Waste Day on October 13, with the support of 19 e-waste companies globally, in order to raise awareness about how large of an issue e-waste has become.

Hazardous waste

A household hazardous waste collection center in Seattle, Washington, U.S.

Under United States environmental policy, hazardous waste is a waste (usually a solid waste) that has the potential to:

cause, or significantly contribute to an increase in mortality or an increase in serious irreversible, or incapacitating reversible illness; or
pose a substantial present or potential hazard to human health or the environment when improperly treated, stored, transported, or disposed of, or otherwise managed.

Under the 1976 Resource Conservation and Recovery Act (RCRA), a facility that treats, stores or disposes of hazardous waste must obtain a permit for doing so. Generators of and transporters of hazardous waste must meet specific requirements for handling, managing, and tracking waste. Through RCRA, Congress directed EPA to issue regulations for the management of hazardous waste. EPA developed strict requirements for all aspects of hazardous waste management including the treatment, storage, and disposal of hazardous waste. In addition to these federal requirements, states may develop more stringent requirements or requirements that are broader in scope than the federal regulations.

EPA authorizes states to implement the RCRA hazardous waste program. Authorized states must maintain standards that are equivalent to and at least as stringent as the federal program. Implementation of the authorized program usually includes activities such as permitting, corrective action, inspections, monitoring and enforcement.

Population

The total U.S. population crossed the 100 million mark around 1915, the 200 million mark in 1967, and the 300 million mark in 2006 (estimated on Tuesday, October 17). The U.S. population more than tripled during the 20th century — a growth rate of about 1.3 percent a year — from about 76 million in 1900 to 281 million in 2000. This is unlike most European countries, especially Germany, Russia, Italy and Greece, whose populations are slowly declining, and whose fertility rates are below replacement.

Population growth is fastest among minorities, and according to the United States Census Bureau's estimation for 2005, 45% of American children under the age of 5 are minorities. In 2007, the nation's minority population reached 102.5 million. A year before, the minority population totaled 100.7 million. Hispanic and Latino Americans accounted for almost half (1.4 million) of the national population growth of 2.9 million between July 1, 2005, and July 1, 2006.

Based on a population clock maintained by the U.S. Census Bureau, the current U.S. population, as of July 2021 is about 332 million. A 2004 U.S. Census Bureau report predicted an increase of one third by the year 2050. A subsequent 2008 report projects a population of 439 million, which is a 44% increase from 2008.

Conservation and environmental movement

Today, the organized environmental movement is represented by a wide range of organizations sometimes called non-governmental organizations or NGOs. These organizations exist on local national and international scales. Environmental NGOs vary widely in political views and in the amount they seek to influence the government. The environmental movement today consists of both large national groups and also many smaller local groups with local concerns. Some resemble the old U.S. conservation movement - whose modern expression is the Nature Conservancy, Audubon Society and National Geographic Society - American organizations with a worldwide influence.

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