Global Warming Research Paper Sources Cited

Guidelines for referring to the works of others in your text using MLA style is covered in chapter six of the MLA Handbook and in chapter seven of the MLA Style Manual. Both books provide extensive examples, so it's a good idea to consult them if you want to become even more familiar with MLA guidelines or if you have a particular reference question.

Basic In-Text Citation Rules

In MLA style, referring to the works of others in your text is done by using what is known as parenthetical citation. This method involves placing relevant source information in parentheses after a quote or a paraphrase.

General Guidelines

  • The source information required in a parenthetical citation depends (1.) upon the source medium (e.g. Print, Web, DVD) and (2.) upon the source’s entry on the Works Cited (bibliography) page.
  • Any source information that you provide in-text must correspond to the source information on the Works Cited page. More specifically, whatever signal word or phrase you provide to your readers in the text, must be the first thing that appears on the left-hand margin of the corresponding entry in the Works Cited List.

In-Text Citations: Author-Page Style

MLA format follows the author-page method of in-text citation. This means that the author's last name and the page number(s) from which the quotation or paraphrase is taken must appear in the text, and a complete reference should appear on your Works Cited page. The author's name may appear either in the sentence itself or in parentheses following the quotation or paraphrase, but the page number(s) should always appear in the parentheses, not in the text of your sentence. For example:

Wordsworth stated that Romantic poetry was marked by a "spontaneous overflow of powerful feelings" (263). Romantic poetry is characterized by the "spontaneous overflow of powerful feelings" (Wordsworth 263). Wordsworth extensively explored the role of emotion in the creative process (263).

The both citations in the examples above, (263) and (Wordsworth 263), tell readers that the information in the sentence can be located on page 263 of a work by an author named Wordsworth. If readers want more information about this source, they can turn to the Works Cited page, where, under the name of Wordsworth, they would find the following information:

Wordsworth, William. Lyrical Ballads. London: Oxford U.P., 1967. Print.

In-text Citations for Print Sources with Known Author

For Print sources like books, magazines, scholarly journal articles, and newspapers, provide a signal word or phrase (usually the author’s last name) and a page number. If you provide the signal word/phrase in the sentence, you do not need to include it in the parenthetical citation.

Human beings have been described by Kenneth Burke as "symbol-using animals" (3). Human beings have been described as "symbol-using animals" (Burke 3).

These examples must correspond to an entry that begins with Burke, which will be the first thing that appears on the left-hand margin of an entry in the Works Cited:

Burke, Kenneth. Language as Symbolic Action: Essays on Life, Literature, and Method. Berkeley: U of California P, 1966. Print.

In-text Citations for Print Sources with No Known Author

When a source has no known author, use a shortened title of the work instead of an author name. Place the title in quotation marks if it's a short work (e.g. articles) or italicize it if it's a longer work (e.g. plays, books, television shows, entire websites) and provide a page number.

We see so many global warming hotspots in North America likely because this region has “more readily accessible climatic data and more comprehensive programs to monitor and study environmental change . . . ” (“Impact of Global Warming” 6).

In this example, since the reader does not know the author of the article, an abbreviated title of the article appears in the parenthetical citation which corresponds to the full name of the article which appears first at the left-hand margin of its respective entry in the Works Cited. Thus, the writer includes the title in quotation marks as the signal phrase in the parenthetical citation in order to lead the reader directly to the source on the Works Cited page. The Works Cited entry appears as follows:

“The Impact of Global Warming in North America.” GLOBAL WARMING: Early Signs. 1999. Web. 23 Mar. 2009.

We'll learn how to make a Works Cited page in a bit, but right now it's important to know that parenthetical citations and Works Cited pages allow readers to know which sources you consulted in writing your essay, so that they can either verify your interpretation of the sources or use them in their own scholarly work.

Author-Page Citation for Classic and Literary Works with Multiple Editions

Page numbers are always required, but additional citation information can help literary scholars, who may have a different edition of a classic work like Marx and Engels's The Communist Manifesto. In such cases, give the page number of your edition (making sure the edition is listed in your Works Cited page, of course) followed by a semicolon, and then the appropriate abbreviations for volume (vol.), book (bk.), part (pt.), chapter (ch.), section (sec.), or paragraph (par.). For example:

Marx and Engels described human history as marked by class struggles (79; ch. 1).

Citing Authors with Same Last Names

Sometimes more information is necessary to identify the source from which a quotation is taken. For instance, if two or more authors have the same last name, provide both authors' first initials (or even the authors' full name if different authors share initials) in your citation. For example:

Although some medical ethicists claim that cloning will lead to designer children (R. Miller 12), others note that the advantages for medical research outweigh this consideration (A. Miller 46).

Citing a Work by Multiple Authors

For a source with three or fewer authors, list the authors' last names in the text or in the parenthetical citation:

Smith, Yang, and Moore argue that tougher gun control is not needed in the United States (76).

The authors state "Tighter gun control in the United States erodes Second Amendment rights" (Smith, Yang, and Moore 76).

For a source with more than three authors, use the work's bibliographic information as a guide for your citation. Provide the first author's last name followed by et al. or list all the last names.

Jones et al. counter Smith, Yang, and Moore's argument by noting that the current spike in gun violence in America compels law makers to adjust gun laws (4).


Legal experts counter Smith, Yang, and Moore's argument by noting that the current spike in gun violence in America compels law makers to adjust gun laws (Jones et al. 4).


Jones, Driscoll, Ackerson, and Bell counter Smith, Yang, and Moore's argument by noting that the current spike in gun violence in America compels law makers to adjust gun laws (4).

Citing Multiple Works by the Same Author

If you cite more than one work by a particular author, include a shortened title for the particular work from which you are quoting to distinguish it from the others.

Lightenor has argued that computers are not useful tools for small children ("Too Soon" 38), though he has acknowledged elsewhere that early exposure to computer games does lead to better small motor skill development in a child's second and third year ("Hand-Eye Development" 17).

Additionally, if the author's name is not mentioned in the sentence, you would format your citation with the author's name followed by a comma, followed by a shortened title of the work, followed, when appropriate, by page numbers:

Visual studies, because it is such a new discipline, may be "too easy" (Elkins, "Visual Studies" 63).

Citing Multivolume Works

If you cite from different volumes of a multivolume work, always include the volume number followed by a colon. Put a space after the colon, then provide the page number(s). (If you only cite from one volume, provide only the page number in parentheses.)

. . . as Quintilian wrote in Institutio Oratoria (1: 14-17).

Citing the Bible

In your first parenthetical citation, you want to make clear which Bible you're using (and underline or italicize the title), as each version varies in its translation, followed by book (do not italicize or underline), chapter and verse. For example:

Ezekiel saw "what seemed to be four living creatures," each with faces of a man, a lion, an ox, and an eagle (New Jerusalem Bible, Ezek. 1.5-10).

If future references employ the same edition of the Bible you’re using, list only the book, chapter, and verse in the parenthetical citation.

Citing Indirect Sources

Sometimes you may have to use an indirect source. An indirect source is a source cited in another source. For such indirect quotations, use "qtd. in" to indicate the source you actually consulted. For example:

Ravitch argues that high schools are pressured to act as "social service centers, and they don't do that well" (qtd. in Weisman 259).

Note that, in most cases, a responsible researcher will attempt to find the original source, rather than citing an indirect source.

Citing Non-Print or Sources from the Internet

With more and more scholarly work being posted on the Internet, you may have to cite research you have completed in virtual environments. While many sources on the Internet should not be used for scholarly work (reference the OWL's Evaluating Sources of Information resource), some Web sources are perfectly acceptable for research. When creating in-text citations for electronic, film, or Internet sources, remember that your citation must reference the source in your Works Cited.

Sometimes writers are confused with how to craft parenthetical citations for electronic sources because of the absence of page numbers, but often, these sorts of entries do not require any sort of parenthetical citation at all. For electronic and Internet sources, follow the following guidelines:

  • Include in the text the first item that appears in the Work Cited entry that corresponds to the citation (e.g. author name, article name, website name, film name).
  • You do not need to give paragraph numbers or page numbers based on your Web browser’s print preview function.
  • Unless you must list the website name in the signal phrase in order to get the reader to the appropriate entry, do not include URLs in-text. Only provide partial URLs such as when the name of the site includes, for example, a domain name, like or as opposed to writing out or

Miscellaneous Non-Print Sources

Werner Herzog's Fitzcarraldo stars Herzog's long-time film partner, Klaus Kinski. During the shooting of Fitzcarraldo, Herzog and Kinski were often at odds, but their explosive relationship fostered a memorable and influential film.

.During the presentation, Jane Yates stated that invention and pre-writing are areas of rhetoric that need more attention.

In the two examples above “Herzog” from the first entry and “Yates” from the second lead the reader to the first item each citation’s respective entry on the Works Cited page:

Herzog, Werner, dir. Fitzcarraldo. Perf. Klaus Kinski. Filmverlag der Autoren, 1982. Film.

Yates, Jane. "Invention in Rhetoric and Composition." Gaps Addressed: Future Work in Rhetoric and Composition, CCCC, Palmer House Hilton, 2002. Print.

Electronic Sources

One online film critic stated that Fitzcarraldo is "...a beautiful and terrifying critique of obsession and colonialism" (Garcia, “Herzog: a Life”).

The Purdue OWL is accessed by millions of users every year. Its “MLA Formatting and Style Guide” is one of the most popular resources (Stolley et al.).

In the first example, the writer has chosen not to include the author name in-text; however, two entries from the same author appear in the Works Cited. Thus, the writer includes both the author’s last name and the article title in the parenthetical citation in order to lead the reader to the appropriate entry on the Works Cited page (see below). In the second example, “Stolley et al.” in the parenthetical citation gives the reader an author name followed by the abbreviation “et al.,” meaning, “and others,” for the article “MLA Formatting and Style Guide.” Both corresponding Works Cited entries are as follows:

Garcia, Elizabeth. "Herzog: a Life." Online Film Critics Corner. The Film School of New Hampshire, 2 May 2002. Web. 8 Jan. 2009.

Stolley, Karl. "MLA Formatting and Style Guide." The OWL at Purdue. 10 May 2006. Purdue University Writing Lab. 12 May 2006 .

Multiple Citations

To cite multiple sources in the same parenthetical reference, separate the citations by a semi-colon:

. . . as has been discussed elsewhere (Burke 3; Dewey 21).

When a Citation Is Not Needed

Common sense and ethics should determine your need for documenting sources. You do not need to give sources for familiar proverbs, well-known quotations or common knowledge. Remember, this is a rhetorical choice, based on audience. If you're writing for an expert audience of a scholarly journal, for example, they'll have different expectations of what constitutes common knowledge.

Historical roots of climate change research

Figures 1 and ​2 show the results from the RPYS based on the climate change research literature in total. The spectrograms show the distribution of the number of cited references across their publication years within the two time periods 1686–1900 and 1900–1970. The earliest cited reference year visible in Fig. 1 is 1686. The earliest reference publication year of the original reference set is the year 1002, but between 1002 and 1686 there are no references with reference counts above the minimum of 10 citations.

Fig. 1

Annual distribution of cited references throughout the time period 1686–1900, which have been cited in climate change papers (published between 1980 and 2014). As a consequence of line smoothing the red curve crosses the zero line. (Color figure...

Fig. 2

Annual distribution of cited references throughout the time period 1900–1970, which have been cited in climate change papers (published between 1980 and 2014). As a consequence of line smoothing the red curve crosses the zero line. (Color figure...

The red lines in Figs. 1 and ​2 visualize the number of cited references per reference publication year. In order to identify those publication years with significantly more cited references than adjacent years, the deviation of the number of cited references in each year from the 5-year median (median of the number of cited references in the two previous, the current, and the two following years: t − 2; t − 1; t; t + 1; t + 2) is also visualized. The deviation from the 5-year median (blue lines) provides a curve smoother than the curve showing absolute numbers (red lines). The blue line makes the distinct peaks more clearly visible. The more recent the references, the less distinct are the peaks, because increasingly more different references per year smooth both the number of cited references and the deviation from the median.

According to Figs. 1 and ​2, there are pronounced peaks in the following 25 reference publication years: 1686, 1735, 1758, 1798, 1847, 1859, 1884, 1896, 1899, 1916, 1932, 1941, 1945, 1948, 1950, 1953, 1957, 1961, 1963, 1964, 1965, 1967, 1968, 1969, and 1970. Table 1 lists the 35 cited references, which comprise the vast majority (or even the complete number) of the cited references of the corresponding reference publication years in Figs. 1 and ​2. As the results in Table 1 show, it is possible that there are two or more important referenced papers within one and the same peak (e.g. see the two cited references with RPY = 1941 or the three cited references with RPY = 1965). Short comments are added, which briefly summarize the content of the cited works and (as far as possible) their relation to climate change research.

Table 1

The most frequently cited references from specific reference publication years in Figs. 1 and ​2, which have been cited by papers dealing with climate change

The numbers of cited references presented in Table 1 are substantially lower than the overall numbers of citations (times cited information of the WoS database records or number of citations based on the WoS cited reference search mode) of the corresponding papers. The main reason for this discrepancy is that a large portion of the references are cited by papers outside the climate change research literature. For example, the key paper by Arrhenius (1896) is also cited by works in geoscience dealing with the carbon cycle. Also, the database records of some relevant papers do not include an abstract and others do not include the search terms of our query in their title or abstract text. Therefore, such papers are not included in our publication set.

Note that the reference counts of all references within a specific reference publication year (i.e. references of the same age) are directly comparable among each other since all citing papers belong to the same research field: climate change research. Thus, the cited references originate in the same citation culture and it is not necessary to field-normalize the cited reference counts as it is conventional in bibliometrics (Waltman 2016). The field-normalization is ensured by the first step of the RPYS: the selection of the publication set on which citation impact is measured target-oriented. However, the corresponding papers of the references presented in Table 1 have been published throughout a large time period (1686–1970) within quite different publication and citation cultures. Thus, the reference counts in the table from different time periods are not comparable with each other. The average (and maximum) number of cited references per paper increases from past to present (Bornmann and Haunschild 2016).

According to Table 1, some of the most frequently cited early publications are most prominent publications of science in general. They are only loosely connected to climate change, in particular the publications by Carolus Linnaeus (CR3), Robert Malthus (CR4), and Charles Darwin (CR6). Their basic nature causes comparatively high citation rates also in the climate change research field. Linnaeus is seen as the father of modern taxonomy and is also considered as one of the founders of modern ecology, where climate plays a major role as driving force. Darwin as the creator of the evolutionary theory was concerned with climate as an important factor of natural selection. Malthus uncovered famine and disease (both often a result of climatic changes) as limiting factors for the growth of population.

Other early works are basic publications in specific disciplines like meteorology (Halley, CR1; Hadley, CR2) or biology (Bergmann, CR5) with a connection to climatology. Edmond Halley identified solar heating as the cause of atmospheric motions and George Hadley discovered that the atmospheric circulation system is intimately related to monsoons and trade winds, the tropical rainbelts, the subtropical deserts, and the jet streams. Carl Bergmann introduced what has been named Bergmann’s rule: A principle that states that populations and species of larger size are found in colder environments, and species of smaller size are found in warmer regions.

These early publications do not mark the beginning of the actual climate change research. The scientific discovery of climate change did not begin before the early nineteenth century when the ice ages and the greenhouse effect were discovered. The first publication, which can be seen as the origin of modern research on climate change, was published 1896 by Arrhenius (CR8). Thus, this paper has been used as marker reference for the co-citation analysis in “Climate research literature citing the marker paper” section below.

The most frequently cited papers published within the first half of the twentieth century are seminal papers in meteorology (Walker and Bliss, CR11), agronomy (Jenny, CR12; Penman, CR16), and climatology (Thornthwaite, CR15). Gilbert Thomas Walker is best known for his groundbreaking description of the Southern Oscillation and for discovering the Walker Circulation. The most frequently cited papers, which appeared in the beginning of the second half of the twentieth century, are related to various fields of geoscience: The publications by Stommel (CR21), Bjerknes (CR32), and Manabe (CR33) deal with oceanic currents, which are major phenomena of global climate. The paper by Manabe and Wetherald (CR27) introduced the first realistic atmospheric model, which considers the convection and radiation budget of the atmosphere. The papers by McCrea (CR17), Epstein et al. (CR18), and Craig and Gordon (CR26) are most important for isotope based dating of ice cores and of all kinds of sediments, whereas the paper by Stokes and Smiley (CR29) gives an introduction to tree-ring dating (dendrochronology). These papers document the importance of research on paleoclimate, both for understanding the earth’s climatic system and for future climate predictions.

The publication by Budyko (CR34) refers to the variations of solar activity as a natural climate factor, which is discussed until present. Blanford (CR7), Penman (CR16), Palmer (CR24), and Monteith (CR25) deal with evaporation and drought, which are decisive factors for agriculture. These are highly topical works in view of the increasing dryness, e.g. in the western part of the USA. The publications by Hutchinson (CR19) and MacArthur and Wilson (CR28) are biosphere related and deal with animal ecology and plant formation or succession. The fundamental work by Milankowitch (CR13) on the causes of glacial periods and by Lorenz (CR22) on chaos theory (see the butterfly effect) are cornerstones of science and have a strong connection to climate change and meteorology, respectively.

Two highly cited pre-1971 publications are the papers by Dansgaard (CR23) and Nash and Sutcliffe (CR35). The paper by Dansgaard (CR23) is most important for the reconstruction of the past climate based on ice core samples. Willi Dansgaard was the first scientist who demonstrated that measurements of the trace isotopes deuterium and oxygen-18 in accumulated glacier ice could be used as an indicator of past climate. The paper by Nash and Sutcliffe (CR35) is one of the first publications about climate change vulnerability. The paper by Hardin (CR31) is an exception in Table 1: “The tragedy of the commons” concept is often cited in connection with sustainable development, meshing economic growth and environmental protection, as well as in the debate of global warming.

Climate research literature citing the marker paper

In the RPYS-CO we substantially reduced the climate change research publication set by using co-citation analysis. Figure 3 shows the spectrogram from the RPYS-CO using the references co-cited with Arrhenius (1896). By definition, the peak associated with this reference is dominating the results. There are two distinct peaks corresponding to references prior to 1896 resulting from the works of forerunners, and six peaks with reference publication years later than 1896. The CRExplorer reveals that the broader peak after 1896 includes three frequently cited papers published between 1897 and 1899. This peak is followed by pronounced peaks corresponding to the reference publication years 1908, 1924, 1938, and 1956/1957 (when modern climate change research began). In order to demonstrate the potential of a more detailed analysis with the CRExplorer, a spectrogram is included in Fig. 3, which is only based on the cited reference years 1800–1850. We zoomed into this time period for an in-depth analysis of the citation pattern of the works of the French mathematician and physicist Jean Baptiste Joseph Fourier, which are sometimes discussed and cited unsatisfactorily in historical overviews on the history of climate change research (see Fleming 1998, 1999).

Fig. 3

Annual distribution of cited references, which are co-cited with Arrhenius (1896) throughout the time period 1686–1970. The curves in the top left corner focus on the time period 1800–1850 as one part of the overall figure. As a consequence...

The cited references underlying the peak reference publication years across the complete time period 1686–1970 in Fig. 3 are listed in Table 2. Due to the narrower focus on the discovery of the greenhouse effect and the specific role of carbon dioxide, there are only two references, which appear in Table 1 as well as in Table 2: the 1896 paper by Arrhenius and the 1899 paper by Chamberlin.

Table 2

The most frequently cited references from specific reference publication years in Fig. 3, which have been co-cited with Arrhenius (1896)

The thematic focus by using the marker reference (COR5) in the RPYS-CO initially reveals the works of two forerunners: (1) the French mathematician and physicist Jean Baptiste Joseph Fourier (COR1–2) is widely seen as the first who detected the greenhouse effect. (2) The Irish physicist John Tyndall (COR3–4) was the first to measure the radiant heat (infrared) absorptive powers of greenhouse gases, including carbon dioxide. Further peaks in the spectrogram can be explained as follows: The American geologist Thomas C. Chamberlin (COR6–8) proposed the possibility that changes in climate could result from changes in the concentration of atmospheric carbon dioxide. The British engineer Guy Callendar (COR10–11) stated that carbon dioxide caused the warming trend of the preceding decades. The Canadian physicist Gilbert N. Plass (COR12–14) calculated the transmission of radiation through the earth’s atmosphere and predicted that doubling the level would bring a 3–4 °C rise. Roger Revelle and Hans E. Suess (COR15) remarked for the first time that mankind had started to embark upon a “large-scale geophysical experiment” as a result of the tremendous utilization of fossil fuels by the industrialized society.

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