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What is temperature?

Temperature is an indicator of the kinetic energy of matter particles; the higher their kinetic energy, the higher the body's temperature. We may qualitatively express the degree of temperature like hot, cold, warm, etc. based on our physiological senses. The earth’s surface temperatures have increased significantly since the beginning of industrialization. Surface temperature is the key component of the earth’s energy balance, which drives weather and climate (Barrows et al., 20017). The figure below illustrates the global mean surface temperature evolution from pre-industrial times.


Shaded area shows the ensemble of models with more than one simulation, and for models with one simulation are shown as thin lines, multi‐model mean (thick red line) and historical observations from GISTEMP (thick black line), Berkeley Earth (dashed black line), and HadCRUT4 (dotted black line). Anomalies are estimated for the 1951–1980 baseline period. (Simon et al., 2020)

How is temperatures measured?

Surface, satellite and balloons - each of these three types of measurements consists of multiple datasets prepared by different teams of data specialists. The datasets are distinguished from one another by differences in the details in their construction. Each type of measurement system as well as each particular dataset has its own unique strengths and weakness (Karl et al.,2006).


The figure illustrates the temperatures variation with altitude in atmosphere.

Surface measurements:

Temperature data comes from fixed weather observing stations with thermometers (glass thermometers containing mercury or some other liquid) used in special instrument shelters.
Other devises to measure temperatures are thermocouples, thermistors, infrared thermometer, resistance temperature detector (RTD), pyrometer, Langmuir probes (for measuring electron temperature of a plasma)

Satellite measurements

Satellite temperature measurements are conclusions about the temperature of the atmosphere at various altitudes, as well as the temperatures of the sea and land surfaces, derived from radiometric observations by satellites. Temperature is not directly measured by weather satellites. To derive indirect inferences of temperature, they measure radiances in various wavelength bands, which must then be computationally inverted. The specifics of the techniques used to derive temperatures from radiances determine the temperature profiles that are produced. As a result, the temperature records created by various groups that studied the satellite data vary. In general, cloud-free circumstances are needed for satellites that measure thermal infrared and use it to recover surface temperatures. The Visible Infrared Imaging Radiometer Suite (VIIRS), the Atmospheric Infrared Sounder (AIRS), the Advanced Very High Resolution Radiometer (AVHRR), Along Track Scanning Radiometers (AASTR), and the ACE Fourier Transform Spectrometer (ACEFTS) on the Canadian SCISAT-1 satellite are a few of the instruments.

Another method for measuring temperature is the occultation of GPS signals. With the use of this method, which gauges how the Earth's atmosphere bends radio signals from GPS satellites, vertical temperature and moisture profiles can be recorded.


The radiosonde is a compact, disposable instrument package that weighs between 250 and 500 grammes. It is positioned beneath a large balloon that has been filled with helium or hydrogen gas. The radiosonde's sensors send pressure, temperature, relative humidity, and GPS position data once per second as it rises at a rate of around 300 metres per minute (or 1,000 feet per minute). These sensors are connected to a battery-operated, 300 milliwatt-or-less radio transmitter that transmits the sensor readings to a sensitive ground tracking antenna on a frequency that normally ranges from 1676 to 1682 MHz or roughly 403
Readings are radio-transmitted back to the data recorder. Ballons are released once or twice a day (00 and/or 12 Coordinated universal Time or UTC. Useful temperature data can be collected from the near surface through the lower and middle stratosphere (not all balloons survive this height (Karl et al., 2006)

Factors affecting the local and global temperatures

The factors affecting the local and global temperatures are as follows:

1.Latitude: The temperature of the surface water decreases from the equator towards the poles because the sun rays become more and more inclined and hence the amount of insolation minimizes poleward.

2.Unequal Distribution of Land and Water: The oceans in the northern hemisphere receive more heat because of their contact with the larger extent of land than the equivalent parts in the southern hemisphere.

3.Prevailing Winds: The winds blowing from the land towards the ocean drive surface water away from the coasts resulting in an upwelling, in which deep cold water rises into the surface.

4.Ocean Current: Warm ocean current increases the temperature in cold areas whereas the cold current decreases the temperature in the warm ocean. For example: in a gulf stream, a warmer current increases the temperature of the Eastern coast of North America and the west coast of Europe.

5.Other factors affecting the temperature distribution are local weather conditions like storms and cyclones.

What  is thermal comfort?

The state of mind known as thermal comfort reflects happiness with the thermal environment and is measured by subjective assessment. When the heat produced by human metabolism is allowed to disperse, thermal neutrality is maintained, maintaining thermal equilibrium with the environment. Although the meaning of "state of mind" or "satisfaction" is left unclear by the definition of thermal comfort, it properly underlines that comfort judgment is a cognitive process incorporating numerous inputs impacted by physical, physiological, psychological, and other aspects [Djongyang et  al., 2010]

If the core body temperature rises to levels of hyperthermia, which is between 37.5 and 38.3 °C, or hypothermia, which is below 35.0 °C, then the thermal environment could be potentially fatal for people. Due to the fact that the average person spends the majority of their time indoors these days, thermal comfort—the mental state that indicates happiness with the thermal environment—is crucial when designing buildings (Joost et al., 2010)

The most commonly used indicator of thermal comfort is air temperature – it is easy to use and most people can relate to it. However, air temperature alone is not a valid or accurate indicator of thermal comfort or thermal stress. It should always be considered in relation to other environmental and personal factors.

The environmental factors include air temperatures, radiant temperatures, air velocity, and humidity. The personal factors include clothing insulation and work rate/metabolic rate.

It has been observed that heat and cold waves condition cause thermal stress to the human body that may lead to various health problems and even a threat to the life.

What are heat and cold waves ?

Extreme temperature events like heat waves and cold waves have a great potential to have a harmful influence on people's health as well as on natural and socioeconomic systems, depending on their length and intensity. (Roberto et al., 2022)

The World Meteorological Organization defines a heat wave as five or more days of sustained heat in which the daily maximum temperature is 5 degrees Celsius or greater than the usual maximum temperature. In India hot weather is experienced in certain parts of India during the months of March to July. Health impacts are dehydration, heat cramps, heat exhaustion, and heatstroke. It also causes weakness, dizziness, headache nausea, muscle cramps and sweating. People living in the extreme temperatures and resultant atmospheric conditions may cause physiological stress and sometimes result in death.

A cold wave is also referred to as a cold snap or cold spell in some areas. It is a weather occurrence connected to the air cooling. A cold wave is described as a rapid drop in temperature over a 24-hour period, and it necessitates significantly heightened protection for social, economic, and industrial operations, according to the U.S. National Weather Service. The speeds at which the temperature drops and the lowest point to which it drops serve as the criteria or basis for a cold wave. It is important to note that the minimum temperature depends on the location and season. A cold air outbreak is what is known as a cold wave when it lasts long enough (CAO). In India, cold and dry winds blow in the north-west India during the months of November and April. Prolonged exposure to cols wave conditions lowers the temperatures of the body as the body loses heat faster than it can produce by muscle contractions, metabolism and shivering. Illness related to cold waves is frostnip, chilblains, frostbite, etc.

It has been observed that heat and cold waves condition cause thermal stress to the human body that may lead to various health problems and even a threat to the life. These also have an adverse impact on the agriculture and industrial production. In many countries, heat and cold waves account for more deaths than any other natural disaster.

6.      What is global warming?

The figure illustrates the global mean temperature difference from baseline period of 1850 to 1900 from multiple datasets, indicating the warming has been increasing rapidly from 1979.

The term "global warming" describes the impact that human activities have on the climate, particularly the burning of fossil fuels (coal, oil, and gas) and extensive deforestation, which release significant amounts of "greenhouse gases" into the atmosphere, the most significant of which is carbon dioxide (Houghton et al., 2005). The temperatures of Earth’s surface has increased significantly since the beginning of industrialization. Global warming is the rise in average temperatures on Earth as a result of greenhouse gases like carbon dioxide produced by burning fossil fuels or logging, which trap heat that would otherwise exit the planet.
The average global annual temperature has risen by just over 1 degree Celsius since the Industrial Revolution. The causes may be natural or anthropogenic. Setting a high price on carbon, expanding the production of biofuels from organic waste, using renewable energy sources like solar and wind power, protecting forests, and enhancing energy efficiency and vehicle fuel economy can all help to reduce it.

The above figure illustrates the trends in degrees Fahrenheit each decade for the global average surface temperature between 1990 and 2021. The planet is warming overall (yellow, orange, red).

Man made factors are deforestation, use of vehicles, use of chlorofluorocarbons (affects the ozone layer which protects earth from harmful ultraviolet radiation emitted by the sun), industrial development (emission from factories), agriculture (methane and carbon dioxide) and overpopulation.
The natural factors incorporate emissions of ash and smoke from volcanoes and changes in the solar radiation incident on earth’s surface.

What is arctic amplification?

The figure illustrates the annual mean temperature evolution in arctic (Mika Rantanen et al. 2022).

Since 1979, the Arctic has warmed almost four times as quickly as the rest of the world (Mika Rantanen et al. 2022). Arctic amplification is the term for how quickly the Arctic has warmed up recently compared to the rest of the world. During the past 43 years, the Arctic has warmed almost four times as quickly as the rest of the world, a larger ratio than is typically stated in literature (Mika Rantanen et al. 2022).

In 2017, Francis explained her findings to the Scientific American: "A lot more water vapor is being transported northward by big swings in the jet stream. That's important because water vapor is a greenhouse gas just like carbon dioxide and methane. It traps heat in the atmosphere. That vapor also condenses as droplets we know as clouds, which themselves trap more heat. The vapor is a big part of the amplification story—a big reason the Arctic is warming faster than anywhere else."

What is the importance of temperatures in the climate science?

Surface temperature is the key component of the earth’s energy balance, which drives weather and climate ( Barrows et al.,2007). Temperature is one of the most important drivers of our climate system. The sun supplies energy to living things directly or indirectly, and it regulates the weather and climate on our world. As the earth shifts in orientation in space over the year, some areas of the planet experience considerable seasonal variations in sunshine intensity due to which some areas are showing higher temperatures than others. The amount of sunlight has an impact on the world's winds, precipitation patterns, and ocean circulation, all of which are climate-related variables. The amount of sunlight has an impact on the world's winds, precipitation patterns, evaporation and ocean circulation. Ocean currents are driven by a combination of Earth’s rotation and temperature difference between the tropics and poles.
The temperature and the amount of moisture can fluctuate on small geographical scales, which we refer to as microclimates. Seasons occur every year, making small-scale temporal variations in climate more predictable. However, when oceanic currents and the movement of air masses are disturbed, alterations could happen. The El Nino-Southern Oscillation is the most well-known instance of this phenomenon.

9.  What are the projected changes in the temperatures and How that would affect the climate change?

The projected changes in temperatures have shown large increases over Arctic than the rest of the world. The global temperatures is expected to grow by 1.4-5.8 C by the end of the 21st century, which would likely increase the magnitude and frequency of extreme events like heat waves, droughts, increased precipitation and wildfires (Benniston et al., 2007;’ IPCC 20076). The future projections of near surface temperatures over India reveal that by the end of twenty-first century, the annual mean temperature over India is projected to increase by 1.02 to 5 °C with respect to the present climate (1995 to 1024) with respect to  SSP5-8.5. The projected changes in temperature with respect to present climate reveal warming of 1.3 to 3.5 °C in mid-future (2060 to 2079) and 1.1 to 5.1 °C in far-future 2080 to 2100. In the case of the far-future period, the annual mean temperature over India is projected to increase by 1.16 °C, 2.40 °C, and 4.7 °C under SSP1-2.6, SSP2-4.5, and SSP5-8.5, respectively.




General circulation models (GCMs) are the primary tools used in today's climate simulations to predict future climate on the basis of well-known physical principles (Randall et al. 2007).









The figure above shows the geographical areas (hotspots of climate-health risks) identified as especially vulnerable to temperature changes in blue color (The Lancet Planetary Health). A variet of SSPs and RCPs scenarios have been used to generate the future projections of climate associated health burdens which are condensed to generate a map of disease hotspot projected by studies [Martinez-Solanas et al, 2021; Chua et al, 2021; Dasgupta et al, 2021; Zhao et al, 2021]

Numerous studies show that continuing greenhouse gas emissions will result in long-term modifications to the climate system and increase the likelihood of broad repercussions from climatic extremes on societal and biological systems ((IPCC 2014; Easterling et al. 2016; Fischer & Knutti 2016; Giorgi et al. 2018; Oppenheimer et al. 2019)). The enhanced warming in mid (1.5 to 2 °C warming world) and far future (more than 3 to 5 °C warming world) poses a serious threat to the rapid melting of glaciers in the Himalayas, and is also likely to affect the frequency of extreme events like flash floods, heat waves, and wildfires, thereby making the population more vulnerable to climate change. 

On a worldwide basis, it is almost clear that throughout the 21st century, there will be a rise in the frequency and size of warm daily temperature extremes and a decrease in cold extremes. Over most land areas, it is quite expected that the length, frequency, and/or intensity of warm spells or heat waves will rise.

By the middle of the twenty-first century, it is predicted that climate change due to rise in temperature would have an impact on food security, with the majority of those affected living in South Asia (IPCC 2014). The population of South Asia is more susceptible to climate change due to the rapid melting of the Himalayan glaciers, increased variability in monsoon rainfall, and increased frequency of catastrophic weather events due to enhanced warming.

Projections from model simulations show that temperatures would rise significantly throughout India towards the end of the century under all scenarios of SSP1-2.6, SSP2-4.5 and SSP5-8.5. Change in temperatures may negatively affect the population, agriculture, energy demand, water supplies, health, forests, ecosystems and the economy. Therefore, it is crucial to comprehend and evaluate the changes in these patterns of temperature change for improved climate policy decisions in the future.

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Data Availability
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