4.6: Accessible Descriptions

Figure 3.1.3 Different Types of Heat Transfers

An educational diagram illustrating four methods of heat transfer: conduction, convection, radiation, and advection. A fire is at the center of the image.

• Convection is shown as upward motion of warm air from the fire toward a pair of hands held above it, indicating heat transfer through the movement of heated air.
• Radiation is shown by wavy lines traveling directly from the fire to another pair of hands held at a distance in front of it, representing direct heat transfer via electromagnetic radiation.
• Conduction is depicted by a person holding a metal rod in their hand, with the opposite end placed in or near the fire. This shows heat traveling through the solid rod from the hot end to the hand.
• Advection is represented by particles or dots moving horizontally away from the heated air, symbolizing horizontal heat transfer through bulk fluid motion.

The diagram is designed to clarify how thermal energy moves in different ways depending on the medium and mechanism.

Figure 3.2.2 The Electromagnetic Spectrum

A labeled diagram of the electromagnetic spectrum focusing on the range of human-visible light. The visible spectrum is positioned between ultraviolet and infrared regions. The top section marks visible wavelengths in nanometers, ranging from 400 to 750 nm. Below it, a horizontal scale shows corresponding electromagnetic categories—such as ultraviolet radiation, infrared radiation, microwaves, and radio waves—with their associated wavelength values (from 1 femtometer to 10 megameters) and frequency values (from 10²⁴ Hz to 10⁴ Hz). Key divisions like cosmic radiation, gamma rays, X-rays, radar, and alternating currents are labeled accordingly.

This diagram illustrates the full electromagnetic spectrum, highlighting the visible portion, which spans wavelengths from approximately 400 to 750 nanometers. The spectrum is organized from left to right by increasing wavelength and decreasing frequency.

To the left of visible light are shorter wavelengths and higher frequencies, representing high-energy radiation. This includes cosmic radiation (starting at about 1 femtometer), gamma rays, and various types of X-rays (hard, medium, and soft). These radiations are mostly invisible and hazardous to biological tissue.

Immediately before the visible spectrum is ultraviolet radiation, divided into UV-C, UV-B, and UV-A types. The visible spectrum lies in the middle of the chart and spans 400 to 750 nanometers. This is the only portion of electromagnetic radiation detectable by the human eye.

To the right of visible light, the wavelengths grow longer, and frequencies drop. This includes infrared radiation, followed by terahertz radiation and microwaves, which are commonly used in communication and cooking appliances.

Beyond these lie radio waves, organized into bands such as ultra-high frequency (UHF), very high frequency (VHF), and others, including shortwave, medium wave, and longwave. At the far right are low-frequency alternating currents with extremely long wavelengths, used in electrical power systems.

The diagram also includes logarithmic scales along the bottom:

• Wavelength, measured in meters, ranges from 10⁻¹⁵ meters to 10⁷ meters.
• Frequency, measured in hertz (Hz), ranges from 10²³ Hz to 10⁻³ Hz.

This spectrum provides a comparative view of how electromagnetic radiation types are distributed by wavelength and frequency, with the visible portion emphasized for reference. More details regarding the exact wavelengths within the spectrum are provided in Table 3.2.1.

Figure 3.3.1: Absorption Spectrum

A scientific diagram titled "Atmospheric Transmission" shows how much electromagnetic radiation is absorbed or scattered by Earth's atmosphere at different wavelengths. The horizontal axis is labeled with wavelength in micrometers and nanometers, ranging logarithmically from approximately 10⁻³ micrometers (gamma rays) to 10⁶ micrometers (radio waves). Major sections along the wavelength axis are labeled as gamma rays, X-rays, ultraviolet, visible, infrared, and radio waves. The vertical axis represents the percentage of atmospheric absorption and/or scattering, from 0% to 100%.

Table \(\PageIndex{1}\): Atmospheric transmission versus wavelength

Wavelength Region	Approx. Wavelength (µm)	Solar Radiation (5525 K)	Earth Thermal Radiation (210–310 K)	Atmospheric Transmission	Dominant Absorbers / Scatterers
Ultraviolet (UV)	0.2–0.4	Present	Negligible	Very low	Ozone, oxygen, Rayleigh scattering
Visible	0.4–0.7	Peak emission	Negligible	Very high (most transmitted)	Minimal absorption
Near Infrared	0.7–3	Moderate	Very low	Variable; many absorption bands	Water vapor, CO₂, O₂, O₃
Mid Infrared	3–8	Very low	Significant	Mostly absorbed except windows	Water vapor, CO₂, CH₄, N₂O
Atmospheric Window	~8–13	Very low	Strong emission	High transmission	Relatively little absorption
Far Infrared	>13–70	Negligible	Declining thermal emission	Mostly absorbed	Water vapor, CO₂

The figure also shows different components such as water vapor, carbon dioxide, oxygen/ozone, methane, and nitrous oxide absorbing different wavelengths of light. A list of the components and their corresponding wavelengths is shown in Table 3.6.2.

Table \(\PageIndex{2}\): Atmospheric absorption components and their contributions

Atmospheric Component	Principal Absorption Regions (Approx. µm)	Relative Contribution
Water Vapor (H₂O)	0.9, 1.1, 1.4, 1.9, 2.7, 5–8, >17	Dominant absorber over much of the infrared
Carbon Dioxide (CO₂)	2.0, 2.7, 4.3, 15	Strong infrared absorption
Oxygen (O₂)	0.76	Narrow absorption band
Ozone (O₃)	UV (<0.35), 9.6	Strong UV absorption and IR band near 9.6 µm
Methane (CH₄)	3.3, 7.7	Moderate infrared absorption
Nitrous Oxide (N₂O)	4.5, 7.8	Moderate infrared absorption
Rayleigh Scattering	Strongest below ~0.5	Scattering decreases rapidly with increasing wavelength

The top panel compares black-body spectra of the Sun (5525 K) and Earth (210–310 K). The peak wavelengths of these curves are shown in Table 3.6.3.

Figure \(\PageIndex{1}\): Blackbody curves and their peak wavelengths.

Temperature	Peak Emission Region	Approximate Peak Wavelength (µm)
5525 K (Sun)	Visible	~0.52
310 K	Infrared	~9.3
260 K	Infrared	~11.1
210 K	Infrared	~13.8

Figure 3.4.1: Carbon Dioxide concentrations in the atmosphere since 1700

A line graph shows the change in atmospheric carbon dioxide (CO₂) concentration over time. The horizontal axis is labeled “Years (C.E.)” and spans from roughly 1700 to the early 2020s. The vertical axis is labeled “CO₂ Concentration (ppm)” and ranges from about 200 to 420 parts per million.

A black line traces the data, with a light blue shaded area beneath it. From 1700 through the mid-1800s, the line is relatively flat, fluctuating slightly around 270–285 ppm. From the late 1800s to about 1950, the line rises gradually to just over 310 ppm. After 1950, the increase becomes steeper and more pronounced, with small, regular up-and-down oscillations visible along the line. The values climb rapidly from around 315 ppm in 1960 to over 410 ppm by the early 2020s.

Text in the upper left reads “Last updated March 26, 2026.”

Key takeaway: CO₂ levels remained fairly stable for about 150 years, then began increasing gradually, followed by a sharp acceleration in the second half of the 20th century through the present.

Figure 3.4.2: The Keeling Curve

This image is a line graph titled “Carbon dioxide concentration at Mauna Loa Observatory.” It shows measurements of atmospheric carbon dioxide (CO₂) concentration over time from approximately 1958 through March 2026. The graph is commonly known as the Keeling Curve, one of the most important long-term records of atmospheric carbon dioxide.

Chart Structure

Horizontal Axis (X-Axis)

• Represents time, beginning around 1958 and extending through 2026.
• Major tick marks are shown at roughly five-year intervals.

Vertical Axis (Y-Axis)

• Represents CO₂ concentration in parts per million (ppm).
• Values range from approximately 310 ppm to 440 ppm.

Data Display

• The data appear as a black line with small points.
• The area beneath the curve is shaded light blue.
• A note indicates that Mauna Kea data are shown in blue when used to supplement the record.
• The graph notes that the record extends through March 26, 2026.

Overall Trend

The graph shows a strong long-term increase in atmospheric carbon dioxide concentration over nearly seven decades.

• In the late 1950s, concentrations were approximately 315 ppm.
• By the mid-1980s, concentrations reached about 345 ppm.
• Around 2000, levels are approximately 370 ppm.
• By 2010, concentrations exceeded 390 ppm.
• Around 2020, values rise above 410 ppm.
• By early 2026, concentrations approach 430 ppm.

The overall pattern is an upward-sloping curve that becomes progressively steeper over time, indicating that atmospheric CO₂ is increasing at an accelerating rate.

Seasonal Oscillations

Superimposed on the long-term rise is a repeating annual zigzag pattern.

Each year:

• CO₂ concentrations rise to a peak.
• Then decline slightly.
• Then rise again the following year.

These seasonal fluctuations typically range from 5 to 10 ppm.

The oscillations occur because:

• Plants in the Northern Hemisphere absorb large amounts of carbon dioxide during the growing season (spring and summer), thereby lowering atmospheric concentrations.
• During fall and winter, plant growth slows and decomposition releases carbon dioxide back into the atmosphere, causing concentrations to increase.

This creates the characteristic sawtooth appearance of the curve.

Key Numerical Changes

Approximate values shown on the graph:

Year	CO₂ Concentration
1958	315 ppm
1970	325 ppm
1980	338 ppm
1990	355 ppm
2000	370 ppm
2010	390 ppm
2020	415 ppm
2026	430 ppm

Overall increase:

• About 115 ppm higher than the initial measurements.
• Represents an increase of roughly 36% compared with 1958 levels.