flash cards Global temperatures PGs 119-134 week 3

Temperature Concepts and Measurement

In Chapter 4, we previously discussed various types of heat and the mechanisms of heat transfer, such as conduction, convection, and radiation. In this chapter, we will delve into the concept of temperature, which, although related to heat, is fundamentally different. It is essential to understand that heat is a form of energy that is transferred among particles within a substance or system through the kinetic energy, or energy of motion, of individual molecules. For instance, in a substance that is relatively hotter, the molecules are moving with greater energy. When more heat is added, it increases the energy of these molecules, resulting in higher kinetic energy and increased molecular motion.

Unlike heat, temperature is not a form of energy. However, it is closely related to the energy present in a substance. Specifically, temperature is a measurement of the average kinetic energy of individual molecules in matter. To clarify, matter can be defined as anything that has mass, occupies space, and assumes a physical shape. Consequently, temperature can be seen as an indicator of heat. It is crucial to remember that heat always flows from regions of higher temperature to those of lower temperature, and this transfer usually causes a change in temperature. For example, when an individual jumps into a cool lake, the kinetic energy leaves their body, transferring heat to the water, thereby lowering the temperature of their skin. It is also noteworthy that heat transfer can occur without a temperature change when a substance changes state, a concept further elaborated in Chapter 7 regarding latent heat transfer.

Temperature Scales

The lowest possible temperature, where atomic and molecular motion ceases entirely, is known as absolute zero, which is equivalent to 0 in absolute temperature terms. This critical point corresponds to 273 degrees Celsius (C), 459.67 degrees Fahrenheit (F), and 0 Kelvin (K). These values are instrumental in understanding the commonly used temperature scales (see Figure 5.3). The Fahrenheit scale, named after its inventor, Daniel G. Fahrenheit, a German physicist, assigns the melting point of ice a value of 32 degrees Fahrenheit, separated by 180 subdivisions from the boiling point of water, which is at 212 degrees Fahrenheit. It's important to note that ice has a distinct melting point, while water can have multiple freezing points that vary based on factors such as purity, volume, and atmospheric conditions.

In contrast, the Celsius scale, developed by the Swedish astronomer Anders Celsius, uses a different approach. He established the melting point of ice as 0 degrees Celsius and defined the boiling temperature of water at sea level as 100 degrees Celsius, dividing his scale into 100 degrees using a decimal system. Consequently, both the Fahrenheit and Celsius scales serve as pivotal tools for measuring temperature, each reflecting the principles of thermal dynamics in their own unique ways.

The Kelvin scale, which was proposed by British physicist Lord Kelvin in 1848, is particularly significant in scientific contexts. It begins at absolute zero, making temperature readings directly proportional to the actual kinetic energy within a material. The melting point for ice on the Kelvin scale is 273 K, while the boiling point of water is represented as 373 K, which is 100 units higher on this scale. It is worth noting that most countries prefer using the Celsius scale for temperature measurement, whereas the United States remains an exception. Nevertheless, continuous pressure from the international scientific community and other organizations indicates that the adoption of the Celsius scale and SI units in the United States is becoming increasingly inevitable.

Measuring Temperature

One of the most familiar instruments for measuring temperature is the thermometer. This device typically comprises a sealed glass tube filled with a fluid that expands and contracts depending on heat changes. For instance, both mercury thermometers and alcohol thermometers are commonly used to measure outdoor temperatures. However, mercury thermometers have their limitations, particularly since mercury freezes at -39°C. Consequently, in colder climates, alcohol thermometers are preferred as alcohol freezes at a significantly lower temperature of -112°C. These thermometers operate on a simple principle: they contain fluid in a small reservoir and are calibrated to measure the expansion or contraction of that fluid, effectively reflecting the temperature of the surrounding environment.

Standardized temperature readings are typically taken from devices placed outdoors within small white shelters, designed for high albedo and proper ventilation to avoid overheating. These shelters are generally positioned at least 1.2 to 1.8 meters above the ground surface, with a common practice being to place them on turf to ensure accuracy. Measures are recorded in the shade to negate the effects of direct sunlight. Inside these instrument shelters, a thermistor is often utilized, which measures temperature by assessing the electrical resistance of a semiconducting material. Since this resistance alters at a rate of approximately 4% per degree Celsius, it enables the conversion of resistance to temperature readings that can then be reported electronically to weather stations.

Daily temperature measurements are conducted at over 16,000 weather stations across the globe, with some stations also tracking the duration of temperature exposure, rates of temperature rise or fall, and temperature variations over the course of the day and night. In 1992, both the World Meteorological Organization and various international climate organizations launched the Global Climate Observing System, which aims to harmonize the reading and recording of temperature and other climate factors among countries. One of its primary objectives is to establish a uniform network of one station per 250,000 square kilometers worldwide, ensuring consistent and accurate climate data collection.

To maintain the integrity of temperature data, organizations like NASA's Goddard Institute for Space Studies continuously refine their methodologies in collecting average temperature measurements. These organizations assess each station to identify potential human activity influences, such as urban heat island effects that may skew data. For locations subjected to human-altered temperature regimes, the long-term temperature trends are adjusted to match average conditions found in surrounding rural areas, where such impacts are negligible. On the other hand, when working with absolute temperature readings, these adjustments are not typically performed. Satellites, too, contribute to temperature data collection, although they do so differently, as they measure land-surface temperature (LST). This differs from air temperature readings, as land-surface temperature can often be much hotter due to the heating effects of solar radiation that land surfaces absorb. Understanding these variations, along with the vital role of thermometers and satellite measurements, helps us appreciate the intricacies involved in accurately monitoring Earth's temperature and climate dynamics.