Directions: Use the information provided and your knowledge of Earth and Space Science to answer the following questions. Show all work where necessary.
Directions: Use the information provided and your knowledge of Earth and Space Science to answer the following questions. Show all work where necessary.
Global atmospheric concentrations of carbon dioxide, methane, nitrous oxide, and certain manufactured greenhouse gases have all risen significantly over the last few hundred years (see Figures 1, 2, 3, and 4).
Historical measurements show that the current global atmospheric concentrations of carbon dioxide, methane, and nitrous oxide are unprecedented compared with the past 800,000 years (see Figures 1, 2, and 3).
Carbon dioxide concentrations have increased substantially since the beginning of the industrial era, rising from an annual average of 280 ppm in the late 1700s to 419 ppm in 2023 (average of five sites in Figure 1) - a 49 percent increase. Almost all of this increase is due to human activities.
The concentration of methane in the atmosphere has more than doubled since preindustrial times, reaching over 1,800 ppb in recent years (see the range of measurements for 2020 through 2023 in Figure 2). This increase is predominantly due to agriculture and fossil fuel use.
Over the past 800,000 years, concentrations of nitrous oxide in the atmosphere rarely exceeded 280 ppb. Levels have risen since the 1920s, however, reaching a new high of 336 ppb in 2022 (average of four sites in Figure 3). This increase is primarily due to agriculture.
Concentrations of many of the halogenated gases shown in Figure 4 were essentially zero a few decades ago but have increased rapidly as they have been incorporated into industrial products and processes. Some of these chemicals have been or are currently being phased out of use because they are ozone-depleting substances, meaning they also cause harm to the Earth’s protective ozone layer. As a result, concentrations of many major ozone-depleting gases have begun to stabilize or decline (see Figure 4, left panel).
Concentrations of other halogenated gases have continued to rise, however, especially where the gases have emerged as substitutes for ozone-depleting chemicals (see Figure 4, right panel).
Overall, the total amount of ozone in the atmosphere decreased by about 4 percent between 1979 and 2020 (see Figure 5). All of the decrease happened in the stratosphere, with most of the decrease occurring between 1979 and 1994. Changes in stratospheric ozone reflect the effect of ozone-depleting substances. These chemicals have been released into the air for many years, but recently, international efforts have reduced emissions and phased out their use.
Globally, the amount of ozone in the troposphere increased by about 12 percent between 1979 and 2020 (see Figure 5).
Since the Industrial Revolution began in the 1700s, people have added a substantial amount of greenhouse gases into the atmosphere by burning fossil fuels, cutting down forests, and conducting other activities (see the U.S. and Global Greenhouse Gas Emissions indicators). When greenhouse gases are emitted into the atmosphere, many remain there for long time periods ranging from a decade to many millennia. Over time, these gases are removed from the atmosphere by chemical reactions or by emissions sinks, such as the oceans and vegetation, which absorb greenhouse gases from the atmosphere. As a result of human activities, however, these gases are entering the atmosphere more quickly than they are being removed from it, and thus their concentrations are increasing.
Carbon dioxide, methane, nitrous oxide, and certain manufactured gases called halogenated gases (gases that contain chlorine, fluorine, or bromine) become well mixed throughout the global atmosphere because of their relatively long lifetimes and because of transport by winds. Concentrations of these greenhouse gases are measured in parts per million (ppm), parts per billion (ppb), or parts per trillion (ppt) by volume. In other words, a concentration of 1 ppb for a given gas means there is one molecule of that gas in every 1 billion molecules of air. Some halogenated gases are considered major greenhouse gases due to their very high global warming potentials and long atmospheric lifetimes even if they only exist at a few ppt (see table).
This figure shows concentrations of carbon dioxide in the atmosphere from hundreds of thousands of years ago through 2023, measured in parts per million (ppm). The data come from a variety of historical ice core studies and recent air monitoring sites around the world. Each line represents a different data source.
This figure shows concentrations of methane in the atmosphere from hundreds of thousands of years ago through 2023, measured in parts per billion (ppb). The data come from a variety of historical ice core studies and recent air monitoring sites around the world. Each line represents a different data source.
This figure shows concentrations of nitrous oxide in the atmosphere from hundreds of thousands of years ago through 2023, measured in parts per billion (ppb). The data come from a variety of historical ice core studies and recent air monitoring sites around the world. Each line represents a different data source.
This figure shows concentrations of several halogenated gases (which contain fluorine, chlorine, or bromine) in the atmosphere, measured in parts per trillion (ppt). The data come from monitoring sites around the world. Note that the scale increases by factors of 10. This is because the concentrations of different halogenated gases can vary by a few orders of magnitude. The numbers following the name of each gas (e.g., HCFC-22) are used to denote specific types of those particular gases.
This figure shows the average amount of ozone in the Earth’s atmosphere each year, based on satellite measurements. The total represents the “thickness” or density of ozone throughout all layers of the Earth’s atmosphere, which is called total column ozone and measured in Dobson units. Higher numbers indicate more ozone. For most years, Figure 5 shows how this ozone is divided between the troposphere (the part of the atmosphere closest to the ground) and the stratosphere. From 1994 to 1996, only the total is available, due to limited satellite coverage.
What pattern do you notice in the concentration of carbon dioxide in the atmosphere from 804,000 BCE to 2023 CE?
Which of the following best explains why carbon dioxide levels have increased so much since 1950?
What pattern do you notice in the concentrations of methane and nitrous oxide from 1950 to 2023 CE?
Study the graphs of greenhouse gases and ozone levels. What overall pattern can you describe about how greenhouse gas concentrations and ozone levels have changed over time?
Claim: Human activities have changed the concentration of greenhouse gases in Earth’s atmosphere.
Evidence:
Reasoning: