5.5: Accessible Descriptions

Figure 4.1.1: Energy Balance and Temperature

Two related graphs show how daily energy balance connects to changes in air temperature over a 24-hour period.

The first graph presents radiation intensity over time. It compares incoming solar radiation, which increases during the day and is absent at night, with outgoing terrestrial radiation, which occurs continuously. Periods when incoming energy is greater than outgoing correspond to warming, while periods when outgoing energy exceeds incoming correspond to cooling.

The second graph shows air temperature over the same time period. Temperature decreases during the night to a minimum in the early morning, rises during the day to a peak later in the day, and then decreases again at night.

The combined message is that changes in temperature follow the balance between incoming and outgoing energy, with a delay between peak energy input and peak temperature.

Figure 4.1.2: Warmest day of the year

Map of North America showing the average timing of the hottest day of the year based on 1991–2020 data. It includes the United States, Canada, Alaska, and Hawaii, with land areas categorized by date. In most regions, the hottest day occurs after the summer solstice, reflecting a seasonal lag between peak solar energy and peak temperature. Many inland areas reach maximum heat in mid-summer, while coastal, higher latitude, and some southern regions peak later, extending into late summer or early fall. Alaska generally shows earlier peak dates than much of the contiguous United States. A legend indicates dates ranging from early June through late October, and the title asks when the hottest day typically occurs under normal conditions.

Figure 4.2.1: Incoming vs. Outgoing radiation with Latitude

Line graph titled “Incoming vs. Outgoing Radiation with Latitude” showing how absorbed solar energy and outgoing terrestrial radiation vary from high southern latitudes through the equator to high northern latitudes. Absorbed solar energy increases from low values at high latitudes to a maximum near the equator, then decreases again toward the opposite pole. Outgoing terrestrial radiation changes more gradually, with values that are relatively higher than absorbed energy at high latitudes and closer to or slightly lower than absorbed energy in low latitudes. The graph identifies an energy surplus in tropical regions where absorbed energy exceeds outgoing radiation, and an energy deficit in higher latitudes where outgoing radiation exceeds absorbed energy. The two values are equal to each other at approximately 38 degrees N/S. Axes are labeled latitude in degrees and radiation intensity in watts per square meter, and a legend distinguishes the two variables.

Figure 4.3.1: Earth's Energy Budget

Infographic titled “Earth’s energy budget” showing the flows and balance of energy entering, moving through, and leaving the Earth system, with values in watts per square meter based on multi-year averages. Incoming solar radiation is about 340.4 W/m². Of this, roughly 99.9 W/m² is reflected back to space, including about 77.0 by clouds and the atmosphere and 22.9 by the surface. The remaining energy is absorbed, with about 77.1 W/m² absorbed by the atmosphere and 163.3 W/m² absorbed by the surface.

The surface releases energy upward primarily as infrared radiation, about 398.2 W/m². The atmosphere absorbs a large portion of this energy, about 358.2 W/m², and re-emits it both upward and downward. Upward emissions include about 169.9 W/m² from the atmosphere and 29.9 W/m² from clouds, with about 40.1 W/m² escaping directly to space through an atmospheric window, contributing to a total outgoing infrared radiation of about 239.9 W/m². Downward emission from the atmosphere back to the surface, often associated with greenhouse gases, is about 340.3 W/m².

Additional energy transfers from the surface to the atmosphere occur through latent heat from evaporation and transpiration, about 86.4 W/m², and through thermals (conduction and convection), about 18.4 W/m². The diagram indicates a small net energy gain of about 0.6 W/m², showing that incoming and outgoing energy are nearly balanced over time. A text box explains that the energy budget includes both radiative processes and non-radiative processes such as conduction, convection, and evaporation, and that, on average, energy entering the system is approximately equal to energy leaving it.

Figure 4.4.4: Albedo and Greenhouse effects of clouds.

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Diagram comparing how clouds affect Earth’s energy during daytime and nighttime.

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In the daytime, incoming sunlight interacts with a cloud, with part of the energy reflected away and part passing through to the surface. This reflection reduces the amount of energy reaching the surface and contributes to cooling, illustrating the albedo effect.

In the nighttime portion, energy emitted from Earth’s surface as longwave radiation rises toward the cloud. The cloud absorbs some of this energy and then emits energy both away from Earth and back toward the surface. The energy returned toward the surface reduces heat loss and contributes to warming, illustrating the greenhouse effect.

Text in the diagram explains that reflection of incoming sunlight leads to cooling during the day, while absorption and re-emission of outgoing longwave radiation leads to warming at night.