Climate and environment glossary – T–Z

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thermal comfort: the level of temperature and humidity that people, on average, find comfortable. This changes depending on numerous factors (eg age, health, activity, clothing). Maintaining thermal comfort is essential for people to live and work effectively, and may involve heating, cooling and (de)humidifying the indoor environment – which often involves the use of energy (and therefore greenhouse gas emissions).

tipping point: the point at which an irreversible chain of events is set in motion. For example, when global temperature rises to a certain level this will trigger a series of catastrophic events, such as the melting of polar ice leading to sea-level rise.

tree hugger: a derogatory term for someone who is concerned about protecting the natural world. The first ‘tree huggers’ were the 363 members of the Bishnoi branch of Hinduism who were killed in 1730 while trying to protect local trees from logging.


UNFCCC: United Nations Framework Convention on Climate Change. See COP.

upcycling: the process of transforming an item instead of throwing it away, changing it into something of greater creative and environmental value. ‘Upcycling’ is relatively recent term for a practice that has existed throughout history, particularly in the developing world. See also downcycling.


waste hierarchy: a tool for controlling and minimising the negative impact of waste, used by businesses and other organisations. It is often represented as a pyramid, from Prevention (Reduce) > Reuse > Recycle > Recovery > Disposal. See also reduce, reuse, recycle, replenish.

Further reading:

wet-bulb temperature (Tw): measured by covering a thermometer bulb with a damp cloth; as the water evaporates from the cloth it cools the thermometer, mimicking the effect of placing a damp cloth on a body to cool it down.

A low wet-bulb temperature means that the air is drier (low humidity), so sweating will do its job of lowering body temperature. When the weather is hot and humidity is high, body temperature cannot be lowered by evaporation of sweat. Severe illness or even death can result from heat stress, and it can trigger other problems with breathing, heart attacks or strokes. At a wet-bulb temperature of over 35°C humans may not survive, even if there is unlimited water and shade, but that can also be true at lower levels (eg in the 2003 European heatwave thousands died although Tw was around 28°C). See thermal comfort.

Further reading:


zero carbon: causing or resulting in no net release of carbon emissions into the atmosphere. See also net zero emissions.