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Dictionary definition of define

We will start by looking at some key definitions commonly used in the field of environmental sustainability. We will be using these definitions throughout the three weeks of the course.

What is climate change and global warming and why is it a problem?

Why are greenhouse gases (GHG) a problem?

The greenhouse effect is a natural process that warms the Earth's surface, to create conditions that are just right to life to thrive. Greenhouse gases are part of Earth's atmosphere. When the Sun's energy reaches the Earth's atmosphere, some of it is reflected back to space and some is absorbed and re-radiated by greenhouse gases. The anthropogenic greenhouse effect is due to greenhouse gases emitted by humans, which amplify the natural greenhouse effect. This leads to global warming. Alt text!

This graphic describes the mechanism of the greenhouse gas effect and global warming. The greenhouse effect is a process that occurs when gases in Earth’s atmosphere trap the Sun’s heat. This process makes Earth much warmer than it would be without an atmosphere.

Global warming

  • Global warming is the long-term heating of Earth’s surface observed since the pre-industrial period (between 1850 and 1900) due to human activities. (United Nations)
  • Not only does it impact health, but it can lead to poor air quality, food and water insecurity, and transmission of climate-sensitive infectious disease.

Climate change

  • Climate is different from weather. Weather describes the atmosphere over a short period of time. Climate is how the atmosphere “behaves” over long periods of time. The National Aeronautics and Space Administration (NASA) describes climate change as the long-term shifts in temperatures and weather patterns on any planet.

The Royal Society have produced a short video called “Climate Change in 60 seconds” which nicely summarises climate change in 60 seconds.

What is sustainability and what is sustainable healthcare?


  • The avoidance of the depletion of natural resources in order to maintain an ecological balance.(Oxford Languages)
  • The idea that goods and services should be produced in ways that do not use resources that cannot be replaced and that do not damage the environment. (Cambridge Dictionary)

Sustainable healthcare

  • The UK Medical Schools Council curriculum provides the best definition of sustainable healthcare.
  • It describes it as “the focus on the improvement of health and better delivery of healthcare, rather than late intervention in disease, with resulting benefits to patients and to the environment on which human health depends, thus serving to provide high-quality healthcare now without compromising the ability to meet the health needs of the future.”

What is planetary health?

  • Described by the Planetary Health Alliance as a “solutions-oriented, transdisciplinary field and social movement.”
  • It assesses and considers the impacts of human activity to the Earth’s natural systems and their impact on human health and all life on Earth.

What is net zero and carbon zero and real zero/true zero?

Net zero

  • Net zero describes the balance between the amount of greenhouse gases (GHG) that are produced and the amount that are removed from the atmosphere. Net zero can be achieved through a combination of reduced emissions and emission removal 1.

Reduced emissions

  • Emission reduction refers to lowering GHG emissions generated by an individual, organisation or country.
  • Emission Reductions (ER) are the measurable reduction of release of GHG into the atmosphere from a specified activity or over a specified area, and a specified period of time measured in a standardised unit of metric ton carbon dioxide equivalent (CO2e).


  • Whatever emissions cannot be reduced are removed or “offset”.
  • Emission removal refers to technologies such as direct air capture and storage (DACS). Direct air capture and storage, DACS, is a technology that uses chemical reactions to pull carbon dioxide out of air. It is currently a very expensive and energy intensive process.
  • Offsetting refers to countries and companies claiming to actively preserve and expand natural carbon sinks such as restoring forests, and conserving wetlands and grasslands in order to “offset” their emission production.
  • Carbon offsetting is a potential loophole which allows for countries, companies and individuals to compensate for their carbon dioxide emissions, by participating in schemes designed to make equivalent reductions of carbon dioxide in the atmosphere. It allows them to still technically meet their emissions targets.

Unfortunately the term net zero is fraught with potential loopholes and pitfalls. We will find out more about this in week 2.

Carbon zero and net zero are often used interchangeably. However, net zero relates to all emissions globally and carbon zero, or ‘neutral’, relates specifically to carbon dioxide.

Real zero/True zero

  • Real zero/True zero means that zero emissions are created or released from a product or service.
  • True zero or real zero will require a near complete transformation of how society currently produces, consumes, and lives. Everything will need to be more efficient, environmentally conscious and less wasteful.

Ecological footprint and carbon footprint

Ecological Footprint

  • Ecological Footprint measures human demand on the natural environment. It compares the total resources people consume with the land and water area that is needed to replace those resources.
  • Carbon footprint also deals with resource usage, but focuses strictly on the GHG released due to burning of fossil fuels.

Carbon footprint

  • Carbon footprint is a measure of the amount of carbon dioxide released into the atmosphere as a result of the activities of a particular individual, organisation, or country.
  • Globally, the average person has a carbon footprint of 4.8 tons of CO2e per year. In contrast, the average American carbon footprint is roughly 20 tons of CO2e per year.
  • To reduce the impact of climate change effects, the average global footprint must drop to 1.87 tons of CO2e before 2050.

The difference between carbon foot and ecological footprint is summarised in the figure below:

This table looks at carbon footprint versus ecological footprint: Carbon footprint measures carbon dioxide generated by activities; only includes carbon emission numbers, Can be used for carbon credit marketplace and directly impacts climate change. Ecological footprint measures renewable and non-renewable resources used; includes both carbon emissions and environmental impact; is used to gauge global consumption and directly impacts continuing life on Earth. Alt text

In step 1.7 we will revisit the definition of carbon footprint in more details.


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How to Drive Sustainable Healthcare: Educate, Engage, and Empower

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