15 Global Climate Change

Learning Objectives

By the end of this chapter, students should be able to:

  • Describe the role of greenhouse gases in  change.
  • Describe the sources of greenhouse gases.
  • Explain Earth’s energy budget and global  changes.
  • Explain how positive and  mechanisms can influence .
  • Explain how we know about climates in the geologic past.
  • Accurately describe which aspects of the environment are changing due to   change.
  • Describe the causes of recent change, particularly the role of humans in the overall balance.

This chapter describes the Earth systems involved in  change, the geologic evidence of past  changes, and the human role in today’s  change. In science, a  is a group of interacting objects and processes. is the study of these systems: —rocks; —gasses; —water; —ice; and —living things. Earth science studies these systems and how they interact and change in response to natural cycles and human-driven, or forces. Changes in one Earth affect other systems.

It is critically important for us to be aware of the geologic context of change processes and how these Earth systems interact, first, for us to understand how and why human activities cause present-day change and, secondly, to distinguish between natural processes and human processes in the geologic past’s record.

A significant part of this chapter introduces and discusses various processes from these Earth systems, how they influence each other, and how they impact global . For example, Earth’s  and largely change based on atmospheric gas , ocean circulation, and the land-surface characteristics of rocks, , and plants.

Also necessary to understanding change is to distinguish between and .  is the short-term and patterns that occur in days and weeks.  is the variable range of and patterns averaged over the long-term for a particular region (see section 13.1). Thus, a single cold winter does not mean that the entire globe is cooling—indeed, the United States’ cold winters of 2013 and 2014 occurred while the rest of the Earth was experiencing record warm-winter temperatures. To avoid these generalizations, many scientists use a 30-year average as a good baseline. Therefore, change refers to slow and changes and trends over the long term for a particular area or the Earth as a whole.

15.1 Earth’s Temperature

Without an , Earth would have huge fluctuations between day and night, like the moon. Daytime temperatures would be hundreds of degrees Celsius above normal, and nighttime temperatures would be hundreds of degrees below normal. Because the Moon doesn’t have much of an , its daytime temperatures are around 106 °C (224℉) and nighttime temperatures are around -183°C (-298℉). That is an astonishing 272°C (522°F) degree range between the Moon’s light side and dark side. This section describes how Earth’s  is involved in regulating the Earth’s .

15.1.1 Composition of Atmosphere

This figure shows the proportion of atmospheric gases at 78% for nitrogen, 21% for oxygen, 1% for argon, and less than 1% for trace components.
Figure 15.1: Composition of the atmosphere.

The ’s  is a key component in regulating the planet’s . The  is 78 percent nitrogen (N2), 21 percent oxygen (O2), one percent argon (Ar), and less than one percent trace components, which are all other gases. Trace components include carbon dioxide (CO2), water vapor (H2O), neon, helium, and methane. Water vapor is highly variable, mostly based on region, and composes about one percent of the . Trace component gasses include several important greenhouse gases, which are the gases responsible for warming and cooling the plant. On a geologic scale,  and the  process, which bury CO2 in , are the ’s CO2 sources. Biological processes both add and subtract CO2 from the .

Greenhouse gases  heat in the  and warm the planet by absorbing some of the longer-wave outgoing infrared radiation that is emitted from Earth, thus keeping heat from being lost to space. More greenhouse gases in the  absorb more longwave heat and make the planet warmer. Greenhouse gasses have little effect on shorter-wave incoming solar radiation.

Four diagrams showing various greenhouse gas molecules: water vapor consists of a red oxygen atom with two white hydrogen atoms attached on the bottom left and bottom right; nitrous oxide consists of two blue nitrogen atoms and a red oxygen atom connected in a straight line; methane consists of a black carbon atom at the center with four white hydrogen atoms connected to the carbon atom in a pyramidal shape; and carbon dioxide consists of a red oxygen atom, a black carbon atom, and another red oxygen atom connected in a straight line.
Figure 15.2: Common greenhouse gases.

The most common greenhouse gases are water vapor (H2O), carbon dioxide (CO2), methane (CH4), and nitrous  (N2O). Water vapor is the most abundant greenhouse gas, but its atmospheric abundance does not change much over time. Carbon dioxide is much less abundant than water vapor, but carbon dioxide is being added to the  by human activities such as burning , land-use changes, and deforestation. Further, natural processes such as  eruptions add carbon dioxide, but at an insignificant rate compared to human-caused contributions.

There are two important reasons why carbon dioxide is the most important greenhouse gas. First, carbon dioxide stays in the and does not go away for hundreds of years. Second, most of the additional carbon dioxide is “” in origin, which means that it is released by burning . For example, and are . and are made from long-dead plant material, which was originally created by photosynthesis millions of years ago and stored in the ground. Photosynthesis takes sunlight plus carbon dioxide and creates the substances of plants. This transformation occurs over millions of years as a slow process, accumulating carbon in rocks and . So, when we burn and , we instantaneously release the stored solar energy and carbon dioxide that took millions of years to accumulate in the first place. The rate of release is critical to comprehend current change.

15.1.2 Carbon Cycle

Critical to understanding global change is to understand the carbon cycle and how Earth’s own carbon-balancing is being rapidly thrown off balance by human-driven activities. Earth has two important carbon cycles: the biological and the geological. In the biological cycle, living organisms—mostly plants—consume carbon dioxide from the to make their tissues and substances through photosynthesis. Then, after the organisms die, and when they decay over years or decades, that carbon is released back into the . The following is the general equation for photosynthesis.

CO2 + H2O + sunlight → sugars + O2

In the geological carbon cycle, a portion of the biological-cycle carbon becomes part of the geological carbon cycle: plant materials into and , tiny fragments and molecules into organic-rich , and the bearing calcareous shells and other parts of organisms into . Such materials become buried and become part of the slow geologic of and other sedimentary materials. This cycle actually involves most of Earth’s carbon and operates very slowly.

A diagram depicting the continuous movement and transformation of carbon on Earth. The diagram shows a circular process with labeled arrows and key components: starting with the emission of carbon into the atmosphere, arrows indicates carbon released from volcanoes, fossil fuel emissions from factories, agriculture, fire, transportation, oceans, and animals; arrows show carbon returning to Earth's surface through plants, oceans, and wetlands; an arrow shows consumption of carbon by animals; and arrows show carbon entering the ground in decomposition. There is an asterisked note in the sky that reads Some carbon remains in the atmosphere (not in cycle) and there is another asterisked note in the ground that says "Some carbon remains in the ground (not in cycle).
Figure 15.3: Carbon cycle.

 The following are geological carbon-cycle storage :

  • Organic matter from plants is stored in peat, , and  for thousands to millions of years.
  •   converts atmospheric carbon dioxide to  bicarbonate, which is stored in the oceans for thousands to tens of thousands of years.
  • organisms convert bicarbonate to forms of , which is stored in rocks for tens to hundreds of millions of years.
  • Carbon compounds are directly stored in  for tens to hundreds of millions of years; some end up in  deposits.
  • Carbon-bearing  are transferred by  to the , where the carbon may be stored for tens of millions to billions of years.
  • Carbon dioxide from within the Earth is released back to the during eruptions, where it is stored for years to decades.

During much of Earth’s history, the geological carbon cycle has been balanced by releasing carbon at approximately the same rate that carbon is stored by the other processes. Under these conditions, Earth’s has remained relatively stable. However, in Earth’s history, there have been times when that balance has been upset. This can happen during prolonged stretches of above-average activity. One example is the Siberian Traps eruption around 250 million years ago, which contributed to strong warming over a few million years.

A carbon imbalance is also associated with significant mountain-building events. For example, the Himalayan Range has been forming for about 40 million years, and over that time—and still today—the rate of on Earth has been enhanced because those mountains are so huge and the range is so extensive that they present a greater surface area on which weathering takes place. The of these rocks—most importantly the of —has resulted in consumption of atmospheric carbon dioxide and transfer of the carbon to the oceans and to ocean-floor -rich . The steady drop in carbon dioxide levels over the past 40 million years, which contributed to the Pliocene-Pleistocene , is partly attributable to the of the Himalayan Range.

Another, nongeological form of carbon-cycle imbalance is happening today on a very rapid time scale. In just a few decades, humans have extracted volumes of , such as , and gas, which were stored in rocks over the past several hundred million years, and converted these fuels to energy and carbon dioxide. By doing so, we are changing the  faster than has ever happened in the past. Remember, carbon dioxide stays in the  and does not go away for hundreds of years. The more greenhouse gases in the , the more heat is trapped and the warmer the planet becomes.

15.1.3 Greenhouse Effect

The  is the reason our global is rising, but it’s important to understand what this effect is and how it occurs. The occurs because greenhouse gases are present in the . The is named after a similar process that warms a greenhouse or a car on a hot summer day. Sunlight passes through the glass of the greenhouse or car, reaches the interior, and changes into heat. The heat radiates upward and gets trapped by the glass windows. The for the Earth can be explained in three steps.

Step 1: Solar radiation from the sun is composed of mostly ultraviolet (UV), visible light, and infrared (IR) radiation. Components of solar radiation include parts with a shorter than visible light, like ultraviolet light, and parts of the spectrum with longer wavelengths, like IR and others. Some of the radiation gets absorbed, scattered, or reflected by the atmospheric gases but about half of the solar radiation eventually reaches the Earth’s surface.

This graph shows the spectrum of solar radiation reaching Earth. The vertical axis show irradiance in Watts per square meter per nanometer increasing upward and the horizontal axis shows wavelength in nanometers increasing toward the right. A smooth and continuous curve shows the irradiance at each wavelength: the curve steeply rises starting at the bottom left of the graph at 0 nm wavelength in a section labeled UV, and the peak of the curve is around 500 nm wavelength and 1.75 irradiance in a section labeled Visible. Then the curve more gradually decreases toward the right in a section labeled Infrared, until it reaches near zero irradiance past 2600 nm wavelength.
Figure 15.4: Incoming radiation absorbed, scattered, and reflected by atmospheric gases.

Step 2: The visible, UV, and IR radiation, that reaches the surface converts to heat energy. Most students have experienced sunlight warming a surface such as pavement, a patio, or deck. When this occurs, the warmer surface then emits thermal radiation, which is a type of IR radiation. So, there is a conversion from visible, UV, and IR to just thermal IR. This thermal IR is what we experience as heat. If you have ever felt heat radiating from a fire or a hot stove top, then you have experienced thermal IR.

Step 3: Thermal IR radiates from the earth’s surface back into the . But since it is thermal IR instead of UV, visible, or regular IR, this thermal IR gets trapped by greenhouse gases. In other words, the sun’s energy leaves the Earth at a different than it enters, so the sun’s energy is not absorbed in the lower when energy is coming in, but rather when the energy is going out. The gases that are mostly responsible for this energy blocking on Earth include carbon dioxide, water vapor, methane, and nitrous . More greenhouse gases in the results in more thermal IR being trapped. Explore this external link to an interactive animation on the greenhouse effect from the National Academy of Sciences.

15.1.4 Earth’s Energy Budget

The solar radiation that reaches Earth is relatively uniform over time. Earth is warmed, and energy or heat radiates from the Earth’s surface and lower back to space. This flow of incoming and outgoing energy is Earth’s energy budget. For Earth’s to be stable over long stretches of time, incoming energy and outgoing energy have to be equal on average so that the energy budget at the top of the balances. About 29 percent of the incoming solar energy arriving at the top of the is reflected back to space by clouds, atmospheric particles, or reflective ground surfaces like sea ice and snow. About 23 percent of incoming solar energy is absorbed in the by water vapor, dust, and ozone. The remaining 48 percent passes through the and is absorbed at the surface. Thus, about 71 percent of the total incoming solar energy is absorbed by the Earth .

This figure shows incoming solar radiation, 23% is absorbed in the atmosphere, 29% reflected, and 48% absorbed at the surface after passing through atmosphere.
Figure 15.5: Incoming solar radiation filtered by the atmosphere.

When this energy reaches Earth, the atoms and molecules that makeup the  and surface absorb the energy, and Earth’s increases. If this material only absorbed energy, then the  of the Earth would continue to increase and eventually overheat. For example, if you continuously run a faucet in a stopped-up sink, the water level rises and eventually overflows. However,  does not infinitely rise because the Earth is not just absorbing sunlight; it is also radiating thermal energy or heat back into the . If the  of the Earth rises, the planet emits an increasing amount of heat to space, and this is the primary mechanism that prevents Earth from continually heating.

Incoming solar radiation reaching the surface (48% net solar energy) and changing into longwave radiation (25% evaporation, 5% convection, 17% net thermal radiation) that radiates into the atmosphere.
Figure 15.6: Some of the thermal infrared energy (heat) radiated from the surface into the atmosphere is trapped by gasses in the atmosphere.

Some of the thermal infrared heat radiating from the surface is absorbed and trapped by greenhouse gasses in the , which act like a giant canopy over Earth. The more greenhouse gases in the , the more outgoing heat Earth retains, and the less thermal infrared heat dissipates to space.

Factors that can affect the Earth’s energy budget are not limited to greenhouse gases. Increasing solar energy can increase the energy Earth receives. However, these increases are very small over time. In addition, land and water will absorb more sunlight when there is less ice and snow to reflect the sunlight back to the . For example, the ice covering the Arctic Sea reflects sunlight back to the ; this reflectivity is called . Furthermore, aerosols (dust particles) produced from burning , diesel engines, and  eruptions can reflect incoming solar radiation and actually cool the planet. While the effect of  aerosols on the ’s  is weak, the effect of human-produced greenhouse gases is not weak. Thus, the net effect of human activity is warming due to more  greenhouse gases associated with  combustion.

Graph with degrees Celsius along the horizontal axis ranging from negative 0.6 on the left to positive 1.3 degrees Celsius on the right. There are black horizontal lines showing the likely ranges and color-coded bars showing the mid-points for warming trends over the 1951–2010 period from greenhouse gases, other anthropogenic forcings, combined anthropogenic forcings, natural forcings, and natural internal climate variability. The observed surface temperature change is shown as a black bar that goes from 0.0 to 0.66 degrees Celsius. Greenhouse gases are shown as a green bar spanning 0.0 to 0.9 degrees C with a black line from 0.5 to 1.3 degrees C; other anthropogenic forcings are shown as a yellow bar spanning negative 0.28 to 0.0 degrees C with a black line from negative 0.6 to 0.1 degrees C; combined anthropogenic forcings are shown as an orange bar spanning 0.0 to 0.7 degrees C with a black line from 0.6 to 0.8 degrees C; natural forcings are shown as a purple bar spanning negative 0.0 to 0.01 degrees C with a black line from negative 0.1 to 0.1 degrees C; and natural internal variability does not have a bar but has a black line from negative 0.1 to 0.1 degrees C.
Figure 15.7: Net effect of factors influencing warming.

An effect that changes the planet can  feedback mechanisms that amplify or suppress the original effect. A  mechanism occurs when the output or effect of a process enhances the original stimulus or cause. Thus, it increases the ongoing effect. For example, the loss of sea ice at the North Pole makes that area less reflective, reducing . This allows the surface air and ocean to absorb more energy in an area that was once covered by sea ice. Another example is melting  is permanently frozen located in the high latitudes, mostly in the Northern Hemisphere. As the warms, more thaws, and the thick deposits of organic matter are exposed to oxygen and begin to decay. This process releases carbon dioxide and methane, which in turn causes more warming, which melts more , and so on and on.

 mechanism occurs when the output or effect reduces the original stimulus or cause. For example, in the short term, more carbon dioxide (CO2) is expected to cause forest canopies to grow, which absorb more CO2. Another example for the long term is that increased carbon dioxide in the will cause more and , which results in transporting dissolved bicarbonate and other ions to the oceans, which are then stored in .

Global warming is evidence that Earth’s energy budget is not balanced. Positive effects on Earth’s are now greater than negative effects.

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15.2 Evidence of Recent Climate Change

While has changed often in the past due to natural causes (see section 14.5.1 and section 15.3), the scientific consensus is that human activity is causing current very rapid change. While this seems like a new idea, it was suggested more than 75 years ago. This section describes the evidence of what most scientists agree is or . For more information, watch the video below on climate change by two professors at the North Carolina State University.

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Video 15.1: Evidence for climate change.

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15.2.1 Global Temperature Rise

The land-ocean index, 1880 to present, compared to a base reference time of 1951-1980, shows ocean temperatures steadily rising. The solid black line is the global annual mean, and the solid red line is the five-year Lowess smoothing. The blue uncertainty bars (95 percent confidence limit) account only for incomplete spatial sampling.

Graph of temperature anomaly on the vertical axis, from -0.6 to 1.0 degrees C, and time on the horizontal axis, from the year 1880 to 2016. The global annual mean land-ocean temperature is plotted on the graph as a solid black line and a solid red line is the five-year Lowess smoothing. The graph shows that the average mean temperature is rising over time, from -0.2 C temperature anomaly in 1880 to 0.98 C temperature anomaly in 2016 with minor fluctuations within the larger trend.
Figure 15.8: Land-ocean temperature index, 1880 to present, with a base time 1951-1980. The solid black line is the global annual mean and the solid red line is the five-year Lowess smoothing. The blue uncertainty bars (95% confidence limit) account only for incomplete spatial sampling. The graph shows that Earth’s temperature is rising.

Since 1880, Earth’s surface-temperature average has trended upward with most of that warming occurring since 1970 (see this NASA animation). Surface temperatures include both land and ocean because water absorbs much additional trapped heat. Changes in land-surface or ocean-surface temperatures compared to a reference from 1951 to 1980, where the long-term average remained relatively constant, are called  . A temperature anomaly thus represents the difference between the measured and the average value during the reference . scientists calculate long-term average temperatures over thirty years or more which identified the reference from 1951 to 1980. Another common range is a century, for example, 1900-2000. Therefore, an of 1.25 ℃ (34.3°F) for 2015 means that the average for 2015 was 1.25 ℃ (34.3°F) greater than the 1900-2000 average. In 1950, the was -0.28 ℃ (31.5°F), so this is -0.28 ℃ (31.5°F) lower than the 1900-2000 average. These temperatures are annual average measured surface temperatures.

This video figure of shows worldwide changes since 1880. The more blue, the cooler; the more yellow and red, the warmer.

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Video 15.2: Earth’s long-term warming trend can be seen in this visualization of NASA’s global temperature record, which shows how the planet’s temperatures are changing over time, compared to a baseline average from 1951 to 1980. The record is shown as a running five-year average.

If you are using an offline version of this text, access this YouTube video via the QR code.

In addition to average land-surface temperatures rising, the ocean has absorbed much heat. Because oceans cover about 70 percent of the Earth’s surface and have such a high specific heat value, they provide a large opportunity to absorb energy. The ocean has been absorbing about 80 to 90 percent of human activities’ additional heat. As a result, in the ocean’s top 701.4 m (2,300 ft) has increased by -17.6°C (0.3℉) since 1969 (watch this 3 minute video by NASA JPL on the ocean’s heat capacity). The reason the ocean has warmed less than the , while still taking on most of the heat, is due to water’s very high specific heat, which means that water can absorb a lot of heat energy with a small increase. In contrast, the lower specific heat of the means it has a higher increase as it absorbs less heat energy.

Some scientists suggest that greenhouse gases do not cause global warming because between 1998 and 2013, Earth’s surface temperatures did not increase much, despite greenhouse gas concentrations continuing to increase. However, since the oceans are absorbing most of the heat, decade-scale circulation changes in the ocean, similar to La Niña, push warmer water deeper under the surface. Once the ocean’s absorption and circulation is accounted for, and this heat is added back into surface temperatures, then increases become apparent, as shown in the figure. Also, the ocean’s heat storage is temporary, as reflected in the record-breaking warm years of 2014-2016. Indeed, with this temporary ocean-storage effect, the twenty-first century’s first 15 of its 16 years were the hottest in recorded history.

15.2.2 Carbon Dioxide

 greenhouse gases, mostly carbon dioxide (CO2), have increased since the industrial revolution when humans dramatically increased burning . These levels are unprecedented in the last 800,000-year Earth history as recorded in geologic sources such as ice cores. Carbon dioxide has increased by 40 percent since 1750, and the rate of increase has been the fastest during the last decade. For example, since 1750, 20409 tonnes (2040 gigatons) of CO2 have been added to the ; about 40 percent has remained in the  while the remaining 60 percent has been absorbed into the land by plants and  or into the oceans. Indeed, during the lifetime of most young adults, the total atmospheric CO2 has increased by 50 ppm, or 15 percent.

Charles Keeling, an oceanographer with Scripps Institution of Oceanography in San Diego, California, was the first person to regularly measure atmospheric CO2. Using his methods, scientists at the Mauna Loa Observatory, Hawaii, have constantly measured atmospheric CO2 since 1957. NASA regularly publishes these measurements at https://keelingcurve.ucsd.edu. Go there now to see the very latest measurement. Keeling’s measured values have been posted in a curve of increasing values, called the Keeling Curve. This curve varies up and down in a regular annual cycle, from summer when the plants in the Northern Hemisphere are using CO2 to winter when the plants are dormant. But the curve shows a steady CO2 increase over the past several decades. This curve increases exponentially, not linearly, showing that the rate of CO2 increase is itself increasing!

Latest CO2 reading: 415.91 ppm.
Figure 15.9: Latest CO2 reading as of September 20, 2022.
Graph showing CO2 concentration in ppm along the vertical axis, from 310 to 430, and year along the horizontal axis, from 1958 to 2022.  The graph shows that the CO2 concentration is rising over time, from 316 ppm in 1958 to 415.91 ppm in 2022 with minor seasonal fluctuations within each year in the larger trend.
Figure 15.10: Keeling curve graph of the carbon dioxide concentration at Mauna Loa Observatory as of September 20, 2022.

The following Atmospheric CO2 video shows how atmospheric CO2 has varied recently and over the last 800,000 years, as determined by an increasing number of CO2 monitoring stations as shown on the insert map. It is also instructive to watch the video’s Keeling portion of how CO2 varies by . This shows that most human CO2 sources are in the Northern Hemisphere where most of the land is and where most of the developed nations are.

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Video 15.3: History of atmospheric CO2 from 800,000 years ago until January 2016. Visit https://gml.noaa.gov/ccgg/trends/ for more information.

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15.2.3 Melting Glaciers and Shrinking Sea Ice

Graph showing Antarctica ice mass in gigatons along the vertical axis, from negative 2000 to 0, and time along the horizontal axis, from the years 2002 to 2016. The graph shows that Antarctic ice mass has declined by 2000 gigatons from 2002 to 2016.
Figure 15.11: Decline of Antarctic ice mass from 2002 to 2016.

are large ice accumulations that exist year round on the land’s surface. In contrast, icebergs are masses of floating sea ice, although they may have had their origin in (see chapter 14). , , and sea ice are all melting. Explore melting at NASA’s interactive Global Ice Viewer). Satellites have recorded that Antarctica is melting at 1189 tonnes (118 gigatons) per year, and Greenland is melting at 2819 tonnes (281 gigatons) per year; 1 metric tonne is 1000 kilograms (1 gigaton is over 2 trillion pounds). Almost all major are shrinking, deflating, and retreating. The ice-mass loss rate is unprecedented—never observed before—since the 1940’s when quality records for began.

Before  warming,  activity was variable with some retreating and some advancing. Now,  snow cover is decreasing, and sea ice is shrinking. Most sea ice is at the North Pole, which is only occupied by the Arctic Ocean and sea ice. The NOAA animation shows how perennial sea ice has declined from 1987 to 2015. The oldest ice is white, and the youngest, seasonal ice is dark blue. The amount of old ice has declined from 20 percent in 1985 to 3 percent in 2015.

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Video 15.4: This animation tracks the relative amount of ice of different ages from 1987 through early November 2015. The oldest ice is white; the youngest (seasonal) ice is dark blue. Key patterns are the export of ice from the Arctic through Fram Strait and the melting of old ice as it passes through the warm waters of the Beaufort Sea. Sea ice age is estimated by tracking of ice parcels using satellite imagery and drifting ocean buoys.

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15.2.4 Rising Sea-Level

Sea level is rising 3.4 millimeters (0.13 inches) per year and has risen 0.19 meters (7.4 inches) from 1901 to 2010. This is thought largely to be from both  melting and thermal expansion of sea water. Thermal expansion means that as objects such as solids, liquids, and gases heat up, they expand in volume.

Classic video demonstration (30 second) on thermal expansion with brass ball and ring (North Carolina School of Science and Mathematics).

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Video 15.5: Thermal expansion.

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15.2.5 Ocean Acidification

Since 1750, about 40 percent of new carbon dioxide has remained in the . The remaining 60 percent gets absorbed by the ocean and vegetation. The ocean has absorbed about 30 percent of that carbon dioxide. When carbon dioxide gets absorbed in the ocean, it creates . This makes the ocean more acidic, which then has an impact on organisms that secrete calcium shells. Recall that hydrochloric acid reacts by effervescing with rock made of , which is calcium . A more acidic ocean is associated with change and is linked to some sea snails (pteropods) and small protozoan zooplanktons’ (foraminifera) thinning shells and to ocean coral ’ declining growth rates. Small animals like protozoan zooplankton are an important component at the base of the ecosystem. Acidification combined with warmer and lower oxygen levels is expected to have severe impacts on ecosystems and human-harvested fisheries, possibly affecting our ocean-derived food sources.

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Video 15.6: Ocean acidification: The other carbon dioxide problem.

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15.2.6 Extreme Weather Events

Extreme events such as hurricanes, , and heatwaves are increasing and becoming more intense. Since the 1980’s, hurricanes, which are generated from warm ocean water, have increased in frequency, intensity, and duration and are likely connected to a warmer . Since 1910, average has increased by 10 percent in the contiguous United States, and much of this increase is associated with heavy events. However, the distribution is not even, and more is projected for the northern United States while less is projected for the already dry southwest. Also, heatwaves have increased, and rising temperatures are already affecting crop yields in northern latitudes. Increased heat allows for greater moisture capacity in the , increasing the potential for more extreme events.

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15.3 Prehistoric Climate Change

Map centered over the North Pole, showing the maximum extent of the Laurentide ice sheet. The ice sheet covers Greenland, Canada, the northern United States, northern Europe, and northern Asia.
Figure 15.12: Maximum extent of Laurentide Ice Sheet.

Over Earth’s history, the  has changed a lot. For example, during the  , the Age of Dinosaurs, the  was much warmer, and carbon dioxide was abundant in the . However, throughout the  , 65 million years ago to today, the  has been gradually cooling. This section summarizes some of these major past  changes.

15.3.1 Past Glaciations

Through geologic history, has changed slowly over millions of years. Before the most recent Pliocene- , there were other major . The oldest, known as the Huronian, occurred toward the end of the -early , about 2.5 billion years ago. The event of that time, the , was a major happening (see chapter 8) most commonly associated with causing that . The increased oxygen is thought to have reacted with the potent greenhouse gas methane, causing cooling.

The end of the  , about 700 million years ago, had other . These ancient are included in the . Widespread global rock sequences from these ancient times contain evidence that existed even in low-latitudes. Two examples are rock—usually formed in tropical environments—and deposits—usually formed in cold climates—have been found together from this time in many regions around the world. One example is in Utah. Evidence of is seen in interbedded and deposits () on Antelope Island in the Great Salt Lake.

The controversial suggests that a runaway effect—where ice and snow reflect solar radiation and increasingly spread from polar regions toward the equator—caused land and ocean surfaces to completely freeze and biological activity to collapse. Thinking is that because carbon dioxide could not enter the then-frozen ocean, the ice covering Earth could only melt when emitted high enough carbon dioxide into the to cause greenhouse heating. Some studies estimate that because of the frozen ocean surface, carbon dioxide 350 times higher than today’s concentration was required. Because biological activity did survive, the complete freezing and its extent in the are controversial. A competing is the Slushball Earth in which some regions of the equatorial ocean remained open. Differing scientific conclusions about the stability of Earth’s magnetic poles, impacts on ancient rock evidence from subsequent , and alternate interpretations of existing evidence keep the idea of controversial.

also occurred in the , notably the Andean-Saharan in the late , about 440–460 million years ago, which coincided with a major event, and the Karoo during the Pennsylvanian Period, 323 to 300 million years ago. This was one of the evidences cited by Wegener for his Continental Drift hypothesis as his proposed drifted into south polar latitudes. The Karoo was associated with an increase of oxygen and a subsequent drop in carbon dioxide, most likely produced by the evolution and rise of land plants.

A graph of atmospheric CO2 levels over time. The vertical axis shows Benthic O-18 in per mil, decreasing upward; the horizontal axis shows the time from 65 to 0 million years ago. During the Cenozoic Era, carbon dioxide levels steadily decreased from a maximum in the Paleocene, causing the climate to gradually cool. By the Pliocene, ice sheets began to form. There are short-term cycles of warming and cooling within the larger glaciation event.
Figure 15.13: Global average surface temperature over the past 65 million years.

During the  —the last 65 million years,  started out warm and gradually cooled to today. This warm time is called the , and Antarctica and Greenland were ice free during this time. Since the Eocene, events during the caused the planet to persistently and significantly cool. For example, the Indian Plate and Asian Plate collided, creating the Himalaya Mountains, which increased the rate of and of , especially . Increased consumes carbon dioxide from the , which reduces the , resulting in long-term cooling.

Map of bottom of earth showing Antarctic continent and an ocean current circulating clockwise around it.
Figure 15.14: The Antarctic Circumpolar Current.

About 40 million years ago, the narrow gap between the South American Plate and the Antarctica Plate widened, which opened the Drake Passage. This opening allowed the water around Antarctica—the Antarctic Circumpolar Current—to flow unrestrictedly west-to-east, which effectively isolated the southern ocean from the warmer waters of the Pacific, Atlantic, and Indian Oceans. The region cooled significantly, and by 35 million years ago, during the Oligocene , had started to form on Antarctica.

Around 15 million years ago, -related  between Central and South America created the Isthmus of Panama, which connected North and South America. This prevented water from flowing between the Pacific and Atlantic Oceans and reduced heat transfer from the tropics to the poles. This reduced heat transfer created a cooler Antarctica and larger Antarctic . As a result, the  expanded on land and water, increased Earth’s reflectivity and enhanced the effect, which created a  loop: more reflective  ice, more cooling, more ice, more cooling, and so on.

By 5 million years ago, during the Pliocene , had started to grow in North America and northern Europe. The most intense part of the current is the Pleistocene ’s last 1 million years. The Pleistocene’s varies significantly through a range of almost 10°C (18°F) on time scales of 40,000 to 100,000 years, and expand and contract correspondingly. These variations are attributed to subtle changes in Earth’s orbital parameters, called (see chapter 14). Over the past million years, the cycles occurred approximately every 100,000 years, with many advances occurring in the last 2 million years (Lisiecki and Raymo, 2005).

Graph showing the oxygen isotope record for last 5 million years with regular minimum-maximum cycles. More pronounced glacial cycles are in the last 1 million years.
Figure 15.15: A Pliocene–Pleistocene stack of 57 globally distributed benthic δ18O records.

During an , of warming are called ; during , very brief of even warmer are called . These warming upticks are related to Earth’s variations, like s, which are changes to the Earth’s orbit that can fluctuate (see chapter 14). In the last 500,000 years, there have been five or six , with the most recent belonging to our current time, the .

The two more recent  swings, the Younger Dryas and the  Climatic Optimum, demonstrate complex changes. These events are more recent, yet have conflicting information. The Younger Dryas’ cooling is widely recognized in the Northern Hemisphere, though the event’s timing, about 12,000 years ago, does not appear to be equal everywhere. Also, it is difficult to find in the Southern Hemisphere. The  Climatic Optimum is a warming around 6,000 years ago; it was not universally warmer, nor as warm as current warming, and not warm at the same time everywhere.

15.3.2 Proxy Indicators of Past Climates

How do we know about past climates? Geologists use proxy indicators to understand past . A  is a biological, chemical, or physical signature preserved in the rock, , or ice record that acts like a fingerprint of something in the past. Thus, they are an indirect indicator of . An indirect indicator of ancient from the and is the Mineral Fork Formation in Utah, which contains rock of such as (). This dark rock has many fine-grained components plus some large out-sized clasts like a modern .

Deep-sea is an indirect indicator of change during the , about the last 65 million years. Researchers from the Ocean Drilling Program, an international research collaboration, collect deep-sea cores that record continuous accumulation. The provides detailed chemical records of stable carbon and oxygen obtained from deep-sea benthic foraminifera shells that accumulated on the over millions of years. The oxygen are a of deep-sea temperatures and ice volume.

Sediment Cores—Stable Oxygen Isotopes

Image of 8 black, gray, brown, and tan sediment cores showing clear layering and vertical changes in color and composition.
Figure 15.16: Sediment core from the Greenland continental slope.

How do oxygen  indicate past ? The two main stable oxygen  are 16O and 18O. They both occur in water (H2O) and in the calcium  (CaCO3) shells of foraminifera as both of those substances’ oxygen component. The most abundant and lighter  is 16O. Since it is lighter, it evaporates more readily from the ocean’s surface as water vapor, which later turns to clouds and  on the ocean and land. This evaporation is enhanced in warmer sea water and slightly increases the concentration of 18O in the surface seawater from which the plankton derives the for its shells. Thus the ratio of 16O and 18O in the fossilized shells in seafloor is a of the and evaporation of seawater.

This figure shows three graphs stacked vertically with the same horizontal axis: 450 thousand years ago on the left to present day on the right. The top two graphs are of Ice Age temperature anomalies over the last 450 thousand years to the present and the bottom graph shows changes in global ice volume over the last 450 thousand years to the present. Changes in global ice volume and changes in Antarctic temperature are highly correlated. Horizontal lines across each graph indicate modern temperature anomaly of 0 and ice volume of Low. The Antarctic temperature records indicate that the present interglacial is relatively cool compared to previous interglacials.
Figure 15.17: Antarctic temperature changes during the last few glaciations compared to global ice volume. The first two curves are based on the deuterium (heavy hydrogen) record from ice cores (EPICA Community Members 2004, Petit et al. 1999). The bottom line is ice volume based on oxygen isotopes from a composite of deep-sea sediment cores (Lisiecki and Raymo 2005).

Keep in mind, it is harder to evaporate the heavier water and easier to condense it. As evaporated water vapor drifts toward the poles and tiny droplets form clouds and , droplets of water with 18O tend to form more readily than droplets of the lighter form and out, leaving the drifting vapor depleted in 18O. During geologic times when the is cooler, more of this lighter that on land is locked in the form of ice. Consider that the giant were more than a mile thick and covered a large part of North America during the last only 14,000 years ago. During , the thus effectively lock away more 16O, thus the ocean water and foraminifera shells become enriched in 18O. Therefore, the ratio of 18O to 16O (𝛿18O) in calcium shells of foraminifera is a of past . The cores from the Ocean Drilling Program record a continuous accumulation of these in the and provide a record of glacials, and .

Sediment Cores—Boron–Isotopes and Acidity

Ocean acidity is affected by and is a proxy for past atmospheric CO2 concentrations. To estimate the ocean’s pH (acidity) over the past 60 million years, researchers collected deep-sea cores and examined the ancient planktonic foraminifera shells’ boron- ratios. Boron has two 11B and 10B. In aqueous compounds of boron, the relative abundance of these two is sensitive to pH (acidity), hence CO2 concentrations. In the early , around 60 million years ago, CO2 concentrations were over 2,000 ppm, higher pH, and started falling around 55 to 40 million years ago, with noticeable drop in pH, indicated by boron ratios. The drop was possibly due to reduced CO2 outgassing from ocean ridges,  and  belts, and increased carbon burial due to and the Himalaya Mountains uplift. By the Miocene , about 24 million years ago, CO2 levels were below 500 ppm, and by 800,000 years ago, CO2 levels didn’t exceed 300 ppm.

Carbon Dioxide Concentrations in Ice Cores

Photo of ice core with visible annual layers; 11 arrows point to lighter-colored summer layers sandwiched between darker winter layers.
Figure 15.18: 19 cm long section of ice core showing 11 annual layers with summer layers (arrowed) sandwiched between darker winter layers.

For the recent Pleistocene ’s , researchers get a more detailed and direct chemical record of the last 800,000 years by extracting and analyzing ice cores from the Antarctic and Greenland . Snow accumulates on these  and creates yearly layers. Oxygen  are collected from these annual layers, and the ratio of 18O to 16O (𝛿18O) is used to determine as discussed above. In addition, the ice contains small bubbles of atmospheric gas as the snow turns to ice. Analysis of these bubbles reveals the of the at these previous times.

A thin section of Antarctic ice showing hundreds of tiny trapped air bubbles. The ice is illuminated with polarized light, producing a colorful effect.
Figure 15.19: Antarctic ice showing hundreds of tiny trapped air bubbles from the atmosphere thousands of years ago.

Small pieces of this ice are crushed, and the ancient air is extracted into a  that can detect the ancient ’s chemistry. Carbon dioxide levels are recreated from these measurements. Over the last 800,000 years, the maximum carbon dioxide concentration during warm times was about 300 parts per million (ppm), and the minimum was about 170 ppm during cold stretches. Currently, the earth’s atmospheric carbon dioxide content is over 410 ppm.

Graph of composite carbon dioxide record: the horizontal axis spans 800,000 years ago on the left to 0 years ago (present day) on the right and the vertical axis spans 170 at the bottom to 310 ppm at the top. CO2 concentrations increase to around 290 ppm during warm periods and decrease to around 190 ppm during glacial periods with approximately 9 regular cycles throughout the graph.
Figure 15.20: Composite carbon dioxide record from last 800,000 years based on ice core data from EPICA Dome C Ice Core.

Oceanic Microfossils

Microfossils, like foraminifera, diatoms, and radiolarians can be used as a proxy to interpret past record. Different species of microfossils are found in the ’s different layers. Microfossil groups are called assemblages and their differs depending on the climatic conditions when they lived. One assemblage consists of species that lived in cooler ocean water, such as in times, and at a different level in the same , another assemblage consists of species that lived in warmer waters.

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Tree Rings

Shows a tree cut in cross-section with tree rings. Each ring form in one year.
Figure 15.21: Tree rings form every year. Rings that are farther apart are from wetter years and rings that are closer together are from dryer years.

Tree rings, which form every year as a tree grows, are another past indicator. Rings that are thicker indicate wetter years, and rings that are thinner and closer together indicate dryer years. Every year, a tree will grow one ring with a light section and a dark section. The rings vary in width. Since trees need much water to survive, narrower rings indicate colder and drier climates. Since some trees are several thousand years old, scientists can use their rings for regional paleoclimatic reconstructions, for example, to reconstruct past , , vegetation, streamflow, sea-surface , and other climate-dependent conditions. Paleoclimatic study means relating to a distinct past geologic climate. Also, dead trees, such as those found in Puebloan ruins, can be used to extend this by showing long-term droughts in the region and possibly explain why villages were abandoned.

Graph of tree ring data: the horizontal axis is labeled Years and spans 5000 BC to 2000 AD; the vertical axis is labeled Anomalies, degrees C, and spans -1 degree Celsius to positive 2 degrees Celsius. Highs and lows fluctuate cyclically throughout time around the 0 degrees celsius line and the last few hundred years are slightly higher temperatures than earlier highs.
Figure 15.22: Summer temperature anomalies for the past 7,000 years.


Scanning electron microscope image of pollen from a variety of common plants: sunflower are small spiky sphericals, colorized pink; morning glory are big sphericals with hexagonal cavities, colorized mint green; hollyhock are big spiky sphericals, colorized yellow; lily are bean shaped, colorized dark green; primrose are tripod shaped, colorized red; and castor bean are small smooth sphericals, colorized light green. The image is magnified some x500, so one bean shaped grain in the bottom left corner is about 50 μm long.
Figure 15.23: Scanning electron microscope image of modern pollen with false color added to distinguish plant species.

Pollen is also a proxy indicator. Flowering plants produce pollen grains. Pollen grains are distinctive when viewed under a microscope. Sometimes, pollen is preserved in lake that accumulate in layers every year. Lake- cores can reveal ancient pollen. -pollen assemblages are pollen groups from multiple species, such as spruce, pine, and oak. Through time, via the cores and radiometric age-dating techniques, the pollen assemblages change, revealing the plants that lived in the area at the time. Thus, the pollen assemblages are a past indicator, since different plants will prefer different climates. For example, in the Pacific Northwest, east of the Cascades in a region close to grassland and forest borders, scientists tracked pollen over the last 125,000 years, covering the last two . As shown in the figure (Fig. 2 from reference Whitlock and Bartlein 1997), pollen assemblages with more pine tree pollen are found during and pollen assemblages with less pine tree pollen are found during times.

Other Proxy Indicators

Paleoclimatologists study many other phenomena to understand past climates, such as human historical accounts, human instrument records from the recent past, lake , cave deposits, and corals.

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15.4 Anthropogenic Causes of Climate Change

As shown in the previous section, prehistoric  changes occur slowly over many millions of years. The  changes observed today are rapid and largely human caused. Evidence shows that  is changing, but what is causing that change? Since the late 1800s, scientists have suspected that human-produced, i.e. changes in atmospheric greenhouse gases would likely cause  change because changes in these gases have been the case every time in the geologic past. By the middle 1900s, scientists began conducting systematic measurements, which confirmed that human-produced carbon dioxide was accumulating in the  and other earth systems, such as forests and oceans. By the end of the 1900s and into the early 2000s, scientists solidified the Theory of Anthropogenic Climate Change when evidence from thousands of ground-based studies and continuous land and ocean satellite measurements mounted, revealing the expected  increase. The  of   Change is that humans are causing most of the current climate changes by burning  such as , and . Theories evolve and  as new data and new techniques become available, and they represent a particular field’s state of thinking. This section summarizes the scientific consensus of   change.

15.4.1 Scientific Consensus

The overwhelming majority of  studies indicate that human activity is causing rapid changes to the , which will cause severe environmental damage. There is strong scientific consensus on the issue. Studies published in peer-reviewed scientific journals show that 97 percent of  scientists agree that  warming is caused from human activities. There is no alternative explanation for the observed link between human-produced greenhouse gas emissions and changing modern . Most leading scientific organizations endorse this position, including the U.S. National Academy of Science, which was established in 1863 by an act of Congress under President Lincoln. Congress charged the National Academy of Science “with providing independent,  advice to the nation on matters related to science and technology.” Therefore, the National Academy of Science is the leading authority when it comes to policy advice related to scientific issues.

One way we know that the increased greenhouse gas emissions are from human activities is with isotopic fingerprints. For example, , representing plants that lived millions of years ago, have a stable carbon-13 to carbon-12 (13C/12C) ratio that is different from today’s atmospheric stable-carbon ratio ( 14C is unstable). Isotopic carbon signatures have been used to identify carbon in the since the 1980s. Isotopic records from the Antarctic Ice Sheet show stable isotopic signatures from ~1000 AD to ~1800 AD and a steady isotopic signature gradually changing since 1800, followed by a more rapid change after 1950 as burning of dilutes the CO2 in the . These changes show the  as having a carbon isotopic signature increasingly more similar to that of .

15.4.2 Anthropogenic Sources of Greenhouse Gases

Pie chart shows greenhouse gas emissions by economic sectors. Total: 49 Gt CO2-eq in 2010. 25% indirect CO2 emissions: energy (1.4%), industry (11%), transport (0.3%), buildings (12%), AFOLU (0.87%). These make up electricity and heat production. 75% indirect CO2 emissions: industry (21%), transport (14%), buildings (6.4%), AFOLU (24%).
Figure 15.24: Total anthropogenic greenhouse gas emissions (gigatonne of CO2-equivalent per year, GtCO2-eq/yr) from economic sectors in 2010. The circle shows the shares of direct GHG emissions (in % of total anthropogenic GHG emissions) from five economic sectors in 2010. The pull-out shows how shares of indirect CO2 emissions (in % of total anthropogenic GHG emissions) from electricity and heat production are attributed to sectors of final energy use.

emissions of greenhouse gases have increased since pre-industrial times due to global economic growth and population growth. Atmospheric concentrations of the leading greenhouse gas, carbon dioxide, are at unprecedented levels that haven’t been observed in at least the last 800,000 years. Pre-industrial level of carbon dioxide was at about 278 parts per million (ppm). As of 2016, carbon dioxide was, for the first time, above 400 ppm for the entirety of the year. Measurements of atmospheric carbon at the Mauna Loa Carbon Dioxide Observatory show a continuous increase since 1957 when the observatory was established from 315 ppm to over 417 ppm in 2022. The daily reading today can be seen at Daily CO2. Based on the ice record over the past 800,000 years, carbon dioxide ranged from about 185 ppm during to 300 ppm during warm times. View the data-accurate NOAA animation below of carbon dioxide trends over the last 800,000 years.

What is the source of these  greenhouse gas emissions?  combustion and industrial processes contributed 78 percent of all emissions since 1970. The economic sectors responsible for most of this include electricity and heat production (25 percent); agriculture, forestry, and land use (24 percent); industry (21 percent); transportation, including automobiles (14 percent); other energy production (9.6 percent); and buildings (6.4 percent). More than half of greenhouse gas emissions have occurred in the last 40 years, and 40 percent of these emissions have stayed in the . Unfortunately, despite scientific consensus, efforts to mitigate  change require political action. Despite growing  change concern, mitigation efforts, legislation, and international agreements have reduced emissions in some places, yet the less developed world’s continual economic growth has increased global greenhouse gas emissions. In fact, the years 2000 to 2010 saw the largest increases since 1970.

Graph of global anthropogenic CO2 emissions: the vertical axis is labeled GtCO2 per year and spans 0 to 40; the horizontal axis is labeled Year and spans 1840 to 2011. The graph is color-coded according to fossil fuel emissions in light gray and forestry and other land use in dark gray. Carbon emissions from fossil fuel combustion increase notably around 1950 and continue to increase consistently until the graph ends in 2011, while forestry and other land use increase around 1950, remain relatively consistent until 2000, and then decrease. To the right of the main graph is a graphic labeled Cumulative CO2 emissions, with two bar graphs labeled 1750-1970 and 1750-2011 and a shared horizontal axis labeled GtCO2 that spans 0 to 2000. The bar graph for 1750-2011 reaches over 2000 GtCO2 while the bar graph for 1750 to 1970 only reaches near 1000 GtCO2. Like with the main graph, the emissions due to fossil fuels are much higher than the emissions due to forestry and other land use in the years 1750-2011.
Figure 15.25: Annual global anthropogenic carbon dioxide (CO2) emissions in gigatonne of CO2-equivalent per year (GtCO2/yr) from fossil fuel combustion, cement production and flaring, and forestry and other land use (FOLU), 1750–2011. Cumulative emissions and their uncertainties are shown as bars and whiskers.

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Included in Earth Science is the study of the of processes that affect surface environments and of the Earth. Recent changes in atmospheric and over intervals of decades have been observed. For Earth’s to be stable, incoming radiation from the sun and outgoing radiation from the sun-warmed Earth must be in balance. Gases in the called greenhouse gases absorb the infrared thermal radiation from the Earth’s surface, trapping that heat and warming the atmosphere, a process called the . Thus the energy budget is not now in balance and the Earth is warming. Human activity produces many greenhouse gases that have accelerated change. CO2 from burning is one of the major ones. While atmospheric is mostly nitrogen and oxygen, trace components including the greenhouse gases (CO2 and methane are the major ones and there are others) have the greatest effect on global warming.

A number of Mechanisms, processes whose results reinforce the original process, take place in the Earth . An example of a PFM of great concern is melting which causes decay of melting organic material that produces CO2 and methane (both powerful greenhouse gases) that warm the and promote more melting. Two carbon cycles affect Earth’s atmospheric CO2 , the biologic carbon cycle and the geologic carbon cycle. In the biologic cycle, organisms (mostly plants and also animals that eat them) remove CO2 from the for energy and to build their body tissues and return it to the when they die and decay. The biologic cycle is a rapid cycle. In the geologic cycle, some organic matter is preserved in the form of and while more is in seawater and captured in , some of which is into the and returned by activity. The geologic carbon cycle is slow over geologic time.

Measurements of increasing atmospheric have been made since the nineteenth century but the upward trend itself increased in the mid twentieth century showing the current trend is exponential. Because of the high specific heat of water, the oceans have absorbed most of the added heat. That this is temporary storage is revealed by the record-breaking warm years of the recent decade and the increase in intense storms and hurricanes. In 1957 the Mauna Loa CO2 Observatory was established in Hawaii providing constant measurements of atmospheric CO2 since 1958. The initial value was 315 ppm. The Keeling curve, named for the observatory founder, shows that value has steadily increased, exponentially, to over 417 ppm now. Compared to proxy data from atmospheric gases trapped in ice cores that show a maximum value for CO2 of about 300 ppm over the last 800,000 years, the Keeling increase of over 100 ppm in 50 years is dramatic evidence of human caused CO2 increase and change! As Earth’s rises, and are shrinking resulting in sea level rise. Atmospheric CO2 is also absorbed in sea water producing increased concentrations of which is raising the pH of the oceans making it harder for life to extract for their skeletal materials.

Earth’s has changed over geologic time with of major . There was a high in the shown by fossils in high latitudes and the Western Interior Seaway covering what is now the Midwest. However, has been cooling during the culminating in the . Since the , several proxy indicators of ancient show that the rate and amount of current change is unique in geologic history and can only be attributed to human activity. Those who ignore the consequences of increasing global warming for our planet’s future do so at the peril of our posterity!

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URLs Linked Within This Chapter

Interactive animation on the greenhouse effect: https://climate.nasa.gov/climate_resources/188/graphic-the-greenhouse-effect/ 

NASA animation: NASA Scientific Visualization Studio (2022), Global Temperature Anomalies from 1880 to 2021 https://svs.gsfc.nasa.gov/4964

3 minute NASA video: NASA JPL, Oceans of Climate Change, https://climate.nasa.gov/climate_resources/40/video-oceans-of-climate-change

Daily CO2: https://www.co2.earth/daily-co2

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Figure References

Figure 15.1: Composition of the atmosphere. NASA. 2019. Public domain. https://climate.nasa.gov/news/2915/the-atmosphere-getting-a-handle-on-carbon-dioxide/#:~:text=By%20volume%2C%20the%20dry%20air,methane%2C%20nitrous%20oxide%20and%20ozone.

Figure 15.2: Common greenhouse gases. Kindred Grey. 2022. CC BY 4.0. Water molecule 3D by Dbc334, 2006 (Public domain, https://commons.wikimedia.org/wiki/File:Water_molecule_3D.svg). Nitrous-oxide-dimensions-3D-balls by Ben Mills, 2007 (Public domain, https://commons.wikimedia.org/wiki/File:Nitrous-oxide-dimensions-3D-balls.png). Methane-CRC-MW-3D-balls by Ben Mills, 2009 (Public domain, https://en.m.wikipedia.org/wiki/File:Methane-CRC-MW-3D-balls.png). Carbon dioxide 3D ball by Jynto, 2011 (Public domain, https://commons.wikimedia.org/wiki/File:Carbon_dioxide_3D_ball.png).

Figure 15.3: Carbon cycle. USGS. 2022. Public domain. https://www.usgs.gov/media/images/usgs-carbon-cycle

Figure 15.4: Incoming radiation absorbed, scattered, and reflected by atmospheric gases. Robert A. Rohde. 2013. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:Solar_spectrum_en.svg

Figure 15.5: Incoming solar radiation filtered by the atmosphere. NASA illustration by Robert Simmon. Astronaut photograph ISS013-E-8948. 2009. Public domain. https://earthobservatory.nasa.gov/features/EnergyBalance/page4.php

Figure 15.6: Some of the thermal infrared energy (heat) radiated from the surface into the atmosphere is trapped by gasses in the atmosphere. NASA illustration by Robert Simmon. Photograph by Cyron, 2006 (CC BY-NC 2.0). https://earthobservatory.nasa.gov/features/EnergyBalance/page5.php

Figure 15.7: Net effect of factors influencing warming. IPCC. 2014. Public domain. https://commons.wikimedia.org/wiki/File:Contributions_to_observed_surface_temperature_change_over_the_period_1951%E2%80%932010.svg

Figure 15.8: Land-ocean temperature index, 1880 to present, with a base time 1951-1980. NASA. 2010. Public domain. https://commons.wikimedia.org/wiki/File:Global_Temperature_Trends.png

Figure 15.9: Latest CO2 reading as of September 20, 2022. Scripps Institution of Oceanography at UC San Diego. 2022. Permissions statement. https://keelingcurve.ucsd.edu/

Figure 15.10: Keeling curve graph of the carbon dioxide concentration at Mauna Loa Observatory as of September 20, 2022. Scripps Institution of Oceanography at UC San Diego. 2022. Permissions statement. https://keelingcurve.ucsd.edu/

Figure 15.11: Decline of Antarctic ice mass from 2002 to 2016. NASA. 2017. Public domain. https://commons.wikimedia.org/wiki/File:ANTARCTICA_MASS_VARIATION_SINCE_2002.png

Figure 15.12: Maximum extent of Laurentide Ice Sheet. USGS. 2005. Public domain. https://commons.wikimedia.org/wiki/File:Pleistocene_north_ice_map.jpg

Figure 15.13: Global average surface temperature over the past 65 million years. Robert A. Rohde. 2005. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:65_Myr_Climate_Change.png

Figure 15.14: The Antarctic Circumpolar Current. Avsa. 2009. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:Conveyor_belt.svg

Figure 15.15: A Pliocene–Pleistocene stack of 57 globally distributed benthic δ18O records. Used under fair use from A Pliocene-Pleistocene stack of 57 globally distributed benthic δ18O records by Lorraine E. Lisiecki, Maureen E. Raymo (https://doi.org/10.1029/2004PA001071).

Figure 15.16: Sediment core from the Greenland continental slope. Hannes Grobe. 2008. CC BY 3.0. https://en.m.wikipedia.org/wiki/File:PS1920-1_0-750_sediment-core_hg.jpg

Figure 15.17: Antarctic temperature changes during the last few glaciations compared to global ice volume. This figure was produced by Robert A. Rohde from publicly available data and is incorporated into the Global Warming Art project. 2012. CC BY-SA 3.0. https://commons.wikimedia.org/wiki/File:Ice_Age_Temperature.png

Figure 15.18: 19 cm long section of ice core showing 11 annual layers with summer layers (arrowed) sandwiched between darker winter layers. NOAA. 2005. Public domain. https://commons.wikimedia.org/wiki/File:GISP2_1855m_ice_core_layers.png?uselang=en-gb

Figure 15.19: Antarctic ice showing hundreds of tiny trapped air bubbles from the atmosphere thousands of years ago. Atmospheric Research, CSIRO. 2000. CC BY 3.0. https://commons.wikimedia.org/wiki/File:CSIRO_ScienceImage_518_Air_Bubbles_Trapped_in_Ice.jpg

Figure 15.20: Composite carbon dioxide record from last 800,000 years based on ice core data from EPICA Dome C Ice Core. Tomruen. 2011. CC BY-SA 3.0. https://commons.wikimedia.org/w/index.php?curid=16147504

Figure 15.21: Tree rings form every year. Arpingstone. 2005. Public domain. https://commons.wikimedia.org/wiki/File:Tree.ring.arp.jpg

Figure 15.22: Summer temperature anomalies for the past 7,000 years. R.M.Hantemirov. 2010. CC BY 3.0. https://commons.wikimedia.org/wiki/File:Yamal50.gif

Figure 15.23: Scanning electron microscope image of modern pollen with false color added to distinguish plant species. Dartmouth Electron Microscope Facility, Dartmouth College. 2011. Public domain. https://en.wikipedia.org/wiki/File:Misc_pollen_colorized.jpg

Figure 15.24: Total anthropogenic greenhouse gas emissions (gigatonne of CO2-equivalent per year, GtCO2-eq/yr) from economic sectors in 2010. Kindred Grey. 2022. CC BY 4.0. Data from IPCC, 2014: Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, R.K. Pachauri and L.A. Meyer (eds.)]. IPCC, Geneva, Switzerland, 151 pp. https://www.ipcc.ch/site/assets/uploads/2018/05/SYR_AR5_FINAL_full_wcover.pdf

Figure 15.25: Annual global anthropogenic carbon dioxide (CO2) emissions in gigatonne of CO2-equivalent per year (GtCO2/yr) from fossil fuel combustion, cement production and flaring, and forestry and other land use (FOLU), 1750–2011. Kindred Grey. 2022. CC BY 4.0. Data from IPCC, 2014: Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, R.K. Pachauri and L.A. Meyer (eds.)]. IPCC, Geneva, Switzerland, 151 pp. https://www.ipcc.ch/site/assets/uploads/2018/05/SYR_AR5_FINAL_full_wcover.pdf


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