The Science of Climate Change: An Introductory Overview

The Science of Climate Change: An Introductory Overview

David I. Spanagel, Ph.D.

Modern climate science has entailed decades of data collection, modeling, and analysis to understand what factors and conditions trigger significant shifts in Earth’s prevailing climate regime. Earth’s climate can best be understood as the aggregate result of a complex system of interactive factors. Like any dynamic system, a changing (rather than fixed) state is to be expected. Since World War II, scientists have sought to attribute the features and tendencies to be found in the aggregate result (our climate) to specific measurable changes observed in any of the components that contribute to the system.

In the International Geophysical Year projects of the late 1950s, scientists began to gather data which led to intriguing insights about global climate. Some proceeded to model the Earth’s climate system by identifying key variables that might “drive” particular kinds of system change. Atmospheric concentrations of carbon dioxide, methane, and nitrous oxides all appeared to be varying over time. Based on initially simplistic linear models of atmospheric chemistry, therefore, some scientists called attention to the importance of these “greenhouse” gases since they tend to trap heat within the Earth’s atmosphere., Further research pursued in the 1970s and 1980s identified even more pronounced greenhouse effect-enhancing halocarbon gases whose presence in the atmosphere could only be explained by their manufacture and dissemination in refrigerants and spray-propellant products.

Similarly, studies of natural variations in the total amount of solar radiation received by the Earth (due to both orbital eccentricities and to rates of solar activity) and due to the aerosol cloud albedo effect (basically, the reflectivity that sends solar radiation back away from the planet) called attention to seasonal changes in cloud types, snow cover, and vegetation patterns. Studies also pointed to the significance of where aerosolized particulates may reside at various altitudes in the atmosphere; such particulates are released both through natural volcanic activity as well as through agricultural, industrial, and military activities.

With longitudinal observational data accumulating, modelers took advantage of improved computing technologies. They developed more sophisticated models that revealed complex relationships among these variables. As in any system, certain kinds of changes may not disturb the aggregate state (especially if variation is kept within a certain range of values). Some researchers looked at the planet’s geological history of cyclic glaciation and concluded that the planet’s climate system might resemble a living body in homeostasis, wherein changes among interacting variables balance or compensate each other to reinforce an overall stability and resilience.

Others noted that an excessive shift in some key variable, or a specific combination of changes among a constellation of variables, have on several occasions so radically destabilized a prevailing state of climate stability that episodes of mass extinctions resulted. Nonlinear feedback mechanisms may trigger such extreme events. With this in mind, studies of oceanic circulation have explored how feedback effects may accelerate the planet towards either global warming or global cooling, based on how a sudden large-scale change in water movement patterns either initiate or terminate widespread redistribution of heat across various latitude zones.

There was never much doubt about whether climate can change; it always has. Research has instead illuminated how differences in any of these subsystems could trigger a dramatic global climate transformation: 1) the sun’s overall energy output; 2) the chemical composition of Earth’s atmosphere; 3) the respective proportions of the planet’s surface taken up by dry land, various vegetation types, open water, and ice sheets; and 4) the dynamics of heat transfer via ocean currents. A series of United Nations Intergovernmental Panel on Climate Change assessment reports successively indicated with increasing specificity and confidence how modern industrial society’s planet-wide activities of deforestation and rapid combustion of hundreds of millions of years’ worth of accumulated fossil fuel hydrocarbons have triggered a now ongoing dramatic transformation of the Earth’s climate. A modest global increase of 1 degree Celsius has already wrought noticeably more frequent violent storms, deglaciation, desertification, ocean acidification, and sea level rise. More will come. +

David I. Spanagel, Ph.D. is associate professor of history in Worcester Polytechnic Institute’s Department of Humanities and Arts. Email: spanagel@wpi.edu.

References

1. Callendar GS. On the amount of carbon dioxide in the atmosphere. Tellus 1958;10(2): 243-248.

2. Keeling C, Whorf T, Wahlen M, and van der Plichtt J. Interannual extremes in the rate of rise of atmospheric carbon dioxide since 1980. Nature 1995;375:666–670.

3.Rasool SI and Schneider SH. Atmospheric carbon dioxide and aerosols: effects of large increases on global climate. Science 1971;173:138–141.

4. Madden RA and Ramanathan V. Detecting climate change due to increasing carbon dioxide. Science 1980;209:763–768.

5. Wang W-C, Yung YL, Lacis AA, Mo T, and Hansen JE. Greenhouse effects due to man-made perturbation of trace gases. Science 1976;194:685– 690.

6. Liousse C, Penner JE, Chuang C, Walton JJ, Eddleman H, and Cachier H. A global three-dimensional model study of carbonaceous aerosols. J. Geophys. Res. Atmos. 1996;101:19411–19432.

7. Hartmann DL, Ockert-Bell ME, and Michelsen ML. The effect of cloud type on Earth’s energy balance: global analysis. J of Climate 1992;5(11):1281–1304.

8. Minnis P, Harrison EF, Stowe LL, Gibson, GG, Denn FM, Doelling DR, and Smith Jr. WL. Radiative climate forcing by the Mount Pinatubo eruption. Science 1993;259(5100):1411–1415.

9. Mitchell Jr, M. A preliminary evaluation of atmospheric pollution as a cause of the global temperature fluctuation of the past century. Singer SF, ed. Global Effects of Environmental Pollution. New York: Springer-Verlag 1970: 139–155.

10. Shaw HR. The periodic structure of the natural record, and nonlinear dynamics. Eos (American Geophysical Union Transactions) 1987;68(50):1651– 1665.

11. Kolbert E. The Sixth Extinction: An Unnatural History. New York: Henry Holt 2014.

12. Barnett TP, Pierce DW, and Schnur R. Detection of anthropogenic climate change in the world’s oceans. Science 2001;292:270–274.

13. Böning C, Dispert A, Visbeck M, Rintoul SR, and Schwarzkopf FU. The response of the Antarctic Circumpolar Current to recent climate change. Nature Geosci 2008;1:864–869.

14.IPCC. First, Second, Third, Fourth, and Fifth Assessment Reports (1990, 1995, 2001, 2007, and 2014, respectively). https://www.ipcc.ch/reports/. Accessed January 13, 2021.

15. NASA Earth Observatory. World of Change: Global Temperatures. https://earthobservatory.nasa. gov/world-of-change/global-temperatures #:~:text=According%20to%20an%20ongoing%20 temperature,2%C2%B0%20Fahrenheit)%20 since%201880. Accessed January 13, 2021.