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Life-cycle Engineering (LCE) is

a sustainability-oriented engineering methodology that takes into account the overall technical, environmental, and economic impacts of decisions within the product life cycle.

SOURCE: Wikipedia 

The product life cycle begins with the raw material extraction stage and ends with disposal, hence the name "cradle-to-grave" approach.

Life-cycle engineering involves applying life-cycle assessment (LCA) to calculate the environmental impacts of a product or process as well as life cycle costing (LCC) to assess the economic effects.

The diagram below shows the main components of a life-cycle assessment. The LCA defines a system boundary and analyses four processes, namely: 

    Raw Materials Acquisition

  Manufacturing

   Operation/Use/Maintenance

    Recycle/Waste Management

The LCA accounts for useful and harmful outputs. 

The overriding objective is to ensure that our human activities do not surpass the carrying capacity of the planet as defined by the nine planetary boundaries. We must operate within these limits to ensure our society does not exploit the Earth beyond its ability to support us.

The 9 Planetary Boundaries

Stratospheric ozone depletion

The use of Ozone-depleting chemical substances allows high-level ultraviolet (UV) radiation to reach ground level. This phenomenon causes higher rates of skin cancer in humans and damages biological systems on land and in the water. Fortunately, because of the Montreal Protocol's actions, we are on track to stay within this boundary.    

Loss of biosphere integrity (biodiversity loss and extinctions)

As the human population grows, the demand for food, water, and natural resources, has caused great losses to biodiversity and significant changes in natural ecosystems. The need for higher agricultural efficiency and the health of the biosphere must be balanced.   

Chemical pollution and the release of novel entities

The release of toxic and long-lived substances into the environment can have potentially irreversible effects on living organisms and our climate. Even when the bioaccumulation of these pollutants (for example, synthetic organic pollutants, heavy metal compounds and radioactive materials) results in sub-lethal levels for organisms, harm to the ecosystem occurs through reduced fertility rates and, possibly, permanent genetic damage. 

Climate Change

According to NASA, the concentration of carbon dioxide in Earth's atmosphere is at nearly 412 parts per million (ppm) and rising. This represents a 47 percent increase since the beginning of the Industrial Age, when the concentration was near 280 ppm, and an 11 percent increase since 2000 when it was near 370 ppm. (Source: NASA, The Atmosphere: Getting a Handle on Carbon Dioxide) 

These levels are higher than the planetary boundary on climate change, damaging the Earth's polar sea-ice, perhaps permanently. Naturally occurring climate feedback loops intensify the Earth's warming, driving it to a warmer state and increasing sea levels by several meters. We will cross another tipping point if we do not stop weakening terrestrial carbon sinks by intentionally destroying the world's rainforests. 

Ocean acidification

Carbon emissions not only affect our air but our oceans as well. Around a quarter of CO2 emissions ultimately end up in the oceans, causing their pH to increase. Surface ocean acidity has increased by 30% compared to pre-industrial times. Under these conditions, corals, some shellfish and plankton have trouble surviving. Like dominoes toppling over, this difficulty rises through the food chain leading to decreased fish stocks.

Freshwater consumption and the global hydrological cycle

By 2050, half a billion people will have difficulty accessing freshwater as a result of our activities, including global-scale changes in river flows and land use. As water becomes scarce, the pressure to intervene further in the natural hydrology will increase, intensifying the problem. The proposed freshwater consumption and environmental flow boundary acts to maintain the overall resilience of the Earth’s water systems.

Land system change

Humans convert the natural landscape of the Earth to live, play and grow food. As our population increases, we convert forests, grassland and wetlands to agricultural land. By doing so, we cause severe reductions in biodiversity, impact water flows, and alter the biogeochemical cycling of carbon, nitrogen, phosphorus, and other vital elements. 

We now know that we must conserve forests to control climate change.  Now we must set a planetary boundary for land systems. In addition to the absolute quantity of land we must also consider its function, quality and geographic distribution.

Nitrogen and phosphorus flows to the biosphere and oceans

The agricultural use of fertilizers has had a dramatic impact on the natural cycles of nitrogen and phosphorus. Surprisingly, most of these elements end up in the atmosphere instead of being taken up by crops. 

Nitrogen-and-phosphorous-laden rain then pollutes water bodies or accumulates in the terrestrial biosphere, destabilizing local ecosystems. Lakes and coastal marine regions become oxygen-starved. 

For example, fertilizer transported by rivers from the US Midwest finds its way to the Gulf of Mexico, forming a 'dead zone' where the decline in the local shrimp catch has been dramatic. 

Atmospheric aerosol loading

Aerosols affect the climate and our healths in many ways. Air pollution affects how clouds form and how air circulates on a global and regional scale. By reflecting or absorbing solar energy, these fine particles in the impact the global climate. Inhaling aerosols affects the healths of living organisms. For example, inhaling highly polluted air causes roughly 800,000 people to die prematurely each year. The toxicological and ecological effects of aerosols are still not well understood. Regardless, a planetary boundary must be defined to limit their impact.

The chart below estimates of how the different control variables for seven planetary boundaries have changed from 1950 to present. The green shaded polygon represents the safe operating space. 

Source: Steffen et al. 2015

The carrying capacity of the Earth is finite. As a result, we must ensure to operate within its limits to ensure our survival.

The IPAT Equation

The IPAT equation is a simple formula expressing the impact of human activity on the environment to the human population, affluence and technology. It is written as,

I = P × A × T

where,

I: human impact on the environment (I), in units of global hectare (gha). This is the ecological footprint of human activities.

P: population (P), in units of number of humans

A: affluence, in units of Gross Domestic Product (GDP) per capita

T: Technology (T)

Let's dive into the details of these terms.

Impact (I)

Ecological footprint calculations can determine I. The ecological footprint per capita indicates how much of the Earth's biologically productive surface is needed to regenerate the resources consumed by the human population.

Affluence (A)

Allfluence refers to the average consumption of each person. As we know, increasing consumption is putting more stress on the environment. Although GDP (Gross Domestic Product) measures production, it can be used as an indication of consumption, or affluence since it stands to reason that as production increases, consumption also increases. 

Technology (T)

T measures how resource-intensive the process of creating, transporting and disposing of the goods and services are. Technology can help mitigate the impact of affluence on the environment by increasing efficiency and using renewable resources. The situation at hand determines what technology indicator to use. For example, to measure the human impact on climate change, greenhouse gas emissions per unit of GDP may be used.

The engineer's role is to analyze the life-cycle of the product or process they are designing from the bottom up using life cycle assessment methods and related tools while being acutely aware of the need to remain with the planetary boundaries. 

Achieving sustainability means reconciling the bottom-up approach of LCA and the top-down approach of the nine planetary boundaries.

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