The successes and failures of societies around the world have been and continue to be dependent on weather and climate, especially because of their critical role in determining the availability of vital agricultural, ecological and hydrological resources. Many of the deities of the earliest civilizations represented weather- and climate-related phenomena, becoming a mechanism for organizing, explaining and passing along relationships and linkages that had been gained from prolonged observation of the timing and variability of seasons, monsoons and other phenomena to future generations. Significant departures from the expected patterns were often memorialized as conflicts between conflicting deities with such fidelity that many of the events have since been identified in paleoclimatic records.

In Greece in the fourth century BCE, Aristotle

Aristotle's treatises described what was known about meteorology, a term of Greek origin meaning atmospheric disturbances.

As exploration and travel expanded, assembly and comparison of information from different regions led to observations of prevailing wind regimes and ocean currents and correlations of phenomena across regions and with geophysical events such as volcanic eruptions. Making progress, however, required both (1) instruments that could quantify observations for analysis and display as maps and (2) advances in understanding of atmospheric physics and chemistry that would eventually provide a more rigorous basis for analysis and forecasting. Advances in both areas were spurred by increasing demands for better understanding of the range of meteorological conditions that could affect public safety, military planning and actions, and expansion of trade and the global economy.

The second and third sections of this paper highlight a number of early advances with relevance to the atmospheric sciences and the gradual awareness about the need for increasing international cooperation to accelerate progress in understanding of atmospheric behaviour and for forecasting. These advances provided essential groundwork that enabled the foundation of the forerunner of today's International Association of Meteorology and Atmospheric Sciences (IAMAS) after the severe historical incision of World War I. The fourth and fifth sections describe the formative years of IAMAS following World War I and then key developments of the association since that time. Tabulated biographical information about the 35 individuals who have served as the president and/or secretary-general is also included to provide a sense of the broad spectrum of interests of those in the international scientific community that have contributed to the development of IAMAS. The sixth section provides a summary of the establishment, primary focus and key scientists that played roles in the formation and development of the 10 international commissions that form the backbone of IAMAS. The final section then contains a few concluding remarks.

The quest for useful observations was significantly advanced in the 1600s when Italian polymath Galileo Galilei invented the thermometer, Italian physicist Evangelista Torricelli invented the barometer and Dutch physicist Christiaan Huygens invented the pendulum clock. During the 18th century, French nobleman Antoine-Laurent de Lavoisier, in addition to organizing understanding of chemistry by establishing the periodic table, was instrumental in identifying that the atmosphere contained, among other components, both oxygen and water vapour, the latter becoming an especially important variable to observe.

By the early 1800s, international trade led to sufficient observations being taken that initial climatological maps could start to be prepared, giving indications of typical conditions by latitude and longitude. It was not until the second half of the 19th century, however, that there were sufficient data and insights to allow preparation of synoptic maps showing such features as cyclonic and anti-cyclonic circulations and indications of their movement in time and changes in intensity. As information was accumulated, climatologies were developed to provide information for improving the routing and safety of the rapidly increasing number of sailing ships. The increasing utility of observations led directors of national meteorological services to agree in the late 19th century to standardize measurement techniques.

Assembly of information was further advanced in 1837 by American Samuel Morse's invention of the telegraph, which soon led to communication lines for rapidly transmitting and receiving observations around the world. The first reliable cable across the Atlantic Ocean began service in 1866, with further installations helping to reduce the time for assembling observations from days and weeks to hours and, starting with the first transatlantic radio communication in 1901, to minutes.

An important limitation to advancing understanding, however, was that virtually all of the regular observations were of conditions at the surface, the few exceptions including cloud type, height and cover (changes of which became an important basis for early weather forecasting); atmospheric scattering (leading to the empirical forecasting adage: “Red sky at night, sailors' delight. Red sky at morning, sailors take warning”; cf. Library of Congress, https://www.loc.gov/rr/scitech/mysteries/weather-sailor.html, last accessed 25 January 2019); sunspot number (as a proxy for changes in solar radiation); and, beginning at a very limited number of locations in the late 19th century, observations of winds aloft using pilot balloons.

Driven by their desire to better understand the weather and climate in the adjacent North Atlantic, Norwegian meteorologist Vilhelm Bjerknes and oceanographer Bjørn Helland-Hansen each established institutes at the University of Bergen in 1917 that were particularly important in advancing understanding of atmospheric fronts, air–sea interactions, and other features that proved essential for forecasting system behaviour over ensuing days. During World War I, aircraft observations aloft started to become available, setting the stage for significant improvement in weather forecasts.

In parallel with the development of observations leading up to the 20th century, advances were made in understanding the physics and chemistry of the atmosphere. The perfect law of gases (also known as Boyle's law after Anglo-Irishman Robert Boyle) and recognition of the three laws of motion put forth by England's Sir Isaac Newton in the late 17th and early 18th centuries provided the foundation for developing an understanding of global atmospheric circulation patterns. In 1735 George Hadley, an amateur English meteorologist, published a paper expanding upon English astronomer Edmond Halley's earlier explanation for the trade winds. Hadley's explanation was based primarily on consideration of the buoyancy of hot air and the Earth's rotation. The resulting circulation he derived featured a single cell extending from the Equator to high latitudes. American William Ferrel reworked the analysis in the 19th century, conserving angular rather than linear momentum, and proposed the three-cell structure recognized today, which has the Ferrel cell located between the low-latitude Hadley cell and the high-latitude Arctic circulation.

In 1824, French scientist Joseph Fourier first published an explanation for the near stability of the Earth's temperature, indicating that downward emission of infrared radiation from the atmosphere played a critical role (Fourier, 1824, 1827). The fundamental laws for thermodynamics were also formulated during the period, with many of the insights coming as a result of seeking to understand the behaviour of gases, particularly those in the atmosphere. In particular, experiments by English physicist (and brewer) James Joule and theoretical work by German physicist Rudolf Clausius established the relationship between work and heat and, with later involvement of William Thomson (later Lord Kelvin), led to the development of the law of conservation of energy as the first law of thermodynamics. Clausius was also responsible for contributing to development of the second law of thermodynamics, which posited that entropy always increases (sometimes stated as heat flows from hot to cold) and deduced what became the Clausius–Clapeyron relationship that, in the meteorological field, determines the saturation water vapour mixing ratio at various temperatures. Adding insights from experimental studies he began in the 1850s, Irish physicist John Tyndall presented proof that water vapour and carbon dioxide (CO2) were the most important atmospheric gases contributing to what is now called the “greenhouse effect”

The term “greenhouse” has become widely used even though the actual physics keeping greenhouses warm is a result of limiting the escape of water vapour from the glass-enclosed structure.

During the same period, Scottish geologist Charles Lyell, building on the reasoning of fellow countryman James Hutton, argued that the Earth's features were a result of slow processes acting over long periods of time (uniformitarianism), rather than being mainly responses to short-term, catastrophic changes, thus rejecting notions derived from biblical genealogies that the Earth's age was only several thousand years. In books first published in the early 1830s, Lyell (1830, 1832, 1833) went on to define and distinguish geological strata (and the climatic conditions that must have been prevailing), clarifying the differences among earlier geological eras (i.e. Palaeozoic, Mesozoic and Cenozoic) and periods (e.g. dividing the Tertiary into the Pliocene, Miocene and Eocene).

Lyell's contributions over the next few decades also contributed critical information underpinning the scientific studies of England's Charles Darwin, setting atmospheric (and geophysical) scientists on a quest to document and explain changes in climate in terms of their causes. The proposal by Swedish scientist Svante Arrhenius in 1896 that changes in the atmosphere's CO2 concentration could help explain Earth's climatic history led directly to his prediction that the future climate would become warmer as a result of ongoing fossil-fuel emissions (Arrhenius, 1896). Through laborious calculations, he became the first scientist to calculate the sensitivity (i.e. responsiveness) of the climate to a doubling of the CO2 concentration, arriving at a value only slightly higher than today's central estimate. That it took over half a century for his hypothesis to be accepted was the result of two key criticisms: (1) the large carbon-holding capacity of the oceans would limit the potential rise in the atmospheric CO2 concentration (a criticism not convincingly refuted until the ocean tracer studies by American oceanographer Roger Revelle and Austro-American chemist Hans Suess in the 1950s; Revelle and Seuss, 1957) and (2) CO2 absorption in the atmosphere was already saturated (a criticism not convincingly refuted until the one-dimensional radiative-convective model simulations of Japanese-American meteorologist Syukuro Manabe and American meteorologist Richard Wetherald in the 1960s showed the importance of the change in altitude at which saturation occurred; Manabe and Wetherald, 1967).

With quantitative understanding developing, British mathematician (and later meteorologist) Lewis Fry Richardson made the first attempt to actually calculate the evolution of the weather over one 6 h time step by quantitatively representing each of the many processes thought to alter atmospheric temperature, water vapour, pressure and winds (Richardson, 1922). Gathering all the available data for 20 May 1910 for a region in central Europe, he spent idle time while serving as an ambulance driver during World War I undertaking the extensive calculations by hand. While the forecast was unsuccessful for various reasons, the stage was set for developing numerical forecasting capabilities over ensuing decades.

Organized international cooperation in meteorology goes back to the mid-19th century, with the first international conference convening in Brussels in 1853 (Ismail-Zadeh, 2016). Naval representatives from 10 nations (eight western European nations plus the USA and Russia) focused their attention on the need to improve and expand observations for weather forecasting. Their efforts eventually led to the first International Meteorological Conference in Vienna in 1873 and the formation of the International Meteorological Organization (IMO) in 1879 (and, much later, inspired the formation of the World Meteorological Organization (WMO) in 1950). The IMO was led by an International Meteorological Committee composed of the directors of the meteorological services of the member nations.

An early example of such international cooperation is documented in the group photograph taken during the summer of 1891 at the International Conference of Directors of Meteorological Services held in Munich, Germany (Fig. 1). Among the 34 attendees from more than a dozen nations on three continents were Georg Neumayer (pioneer of Southern Hemisphere meteorology) and Wilhelm von Bezold (thermodynamicist who defined potential temperature) from Germany, Cleveland Abbe (early proponent of dynamical meteorology) from the USA, Julius Hann (global-scale collector of vast climatological datasets) from Austria, and Léon Teiserrenc de Bort (specialist in vertical soundings and co-discoverer of the stratosphere a decade later) from France. Although most participants represented fledging meteorological services, they met as experts in a personal, non-governmental capacity and set out to distribute tasks among technical commissions (Davies, 1990, p. 4), as is still done by both IAMAS and WMO. The International Commission on Radiation and Insolation formed in 1896 (Bolle, 2008) and the International Commission for the Scientific Investigation of the Upper Air were two of the very early commissions.

As World War I was coming to a close in late 1918, leading scientists in the allied nations began advancing plans for peaceful cooperation and scientific advancement under the League of Nations. That international cooperation in the development and application of meteorological observations and forecasting had been going on for a half-century provided a strong basis for the effort to expand such cooperation across a broader spectrum of the geophysical sciences. Led by representatives of the national academies of science of the various nations

That leaders of meteorological sciences in the national academies were also often leaders in their government's activities was relatively unique across the geophysical sciences, showing in a very real sense how scientific advances in atmospheric sciences could rapidly be applied by governments for the benefit and safety of their citizens and economic and governmental activities.

At the Brussels plenary, Sir Napier Shaw of UK's Royal Society was appointed President of the Bureau for the Section de Météorologie, hereafter referred to as the Meteorology Section. Shaw had emphasized greater reliance on science (as opposed to empirical analysis) in his leadership of the British Meteorological Office during World War I (including by employing Lewis Richardson). Charles Alfred Angot, earlier Directeur du Bureau Central Météorologique de France, was selected as vice president, and Charles F. Marvin, then chief of the US Weather Bureau, was selected as secretary (Bauer, 1919b). While each had been or was a leader of their government's meteorological service, the Meteorology Section was a creation of the national academies of science of the participating countries rather than of government meteorological organizations. The focus of the non-governmental effort was intended to be on the scientific questions arising in the study of meteorology and geophysics in contrast to the more empirical and observational emphasis of the governmental efforts that were focused mainly on operational forecasting and ensuring public safety. That these efforts had been ongoing together for so long provided a strong basis for their ongoing cooperation and connection.

Each nation was called upon to have a national committee for IUGG, providing a member to serve as a representative to each of its sections; this requirement proved instrumental in spurring organization and cooperation among each of the disciplines in the member countries. Members of the atmospheric science community were active participants in the organizational efforts (Shaw, 1923). For example, climatologist Hubert Lamb was included along with those affiliated with the UK Meteorological Service as UK's representatives; France formed an IUGG national committee, of which 49 of its 124 members were affiliated with the Section of Meteorology; and in the USA, formation of the national committee spurred organization in 1919 of both the American Meteorological Society and what later became the American Geophysical Union (Wood, 1920).

The photograph of participants at the eighth meeting of the International Commission for the Scientific Investigation of the Upper Air (Fig. 2) held in Bergen, Norway, in 1921 shows many of those who were engaged with the early development of the Section of Meteorology, including Sir Napier Shaw (the section's founding president), Vilhelm Bjerknes (who served as president from 1935–1936) and his son Jacob Bjerknes (who served as secretary-general from 1936 to 1948 and president from 1951–1954). Right from the beginning, the enthusiasm for international cooperation on a voluntary basis appears to have been a natural and steady ingredient of most gatherings of IUGG's sections and their successors (cf. Gold, 1921; Volkert, 2017). A brief but vivid eyewitness account was provided some 55 years after the meeting in Bergen by Schereschewsky (1977), including succinct appraisals of later achievements by some of the participants.

By providing their sections with an annual allocation from the collective dues paid by the national academy of each of the 20 initial member nations, IUGG provided resources for their Sections to actually organize research activities. This was in contrast to the IMO, which did not at that time provide funds to promote cooperative activities. That this effort to promote international research was seen as a particularly important endeavour by the participating nations is suggested by the fact that the US Congress explicitly endorsed the effort and specifically allocated funding for IUGG membership in its annual budget actions over IUGG's first several years.

The first major action of the Meteorology Section's Bureau was to call for proposals from the national committees for research topics and questions to be placed on the agenda for the first IUGG general assembly to be held in Rome in 1922. In his report to the Royal Meteorological Society, Shaw (1923) explained 11 topical areas (or “gaps of knowledge”) that had been submitted by the national committees of Great Britain, France and Italy (collected in Table 1). Many of the suggested topics continued to be of such interest that they later became the basis for formation of many of the commissions that now exist.

Nine nations are reported to have sent delegates to the first meeting of the Meteorology Section at the Rome general assembly: Australia, Belgium, France, Great Britain, Italy (in large numbers), Portugal, Spain, Sweden and the USA. Resolutions approved were related to the following subjects (Kimball, 1922), which were closely linked to the above-mentioned topical areas:

allocating much of the Section's funding to initiate an enhanced network of balloon sondes to explore the upper atmosphere;

Following the general assembly in Rome in 1922, the Meteorology Section met every 3 years (except for the years during World War II) as part of the triennial general assemblies of IUGG until the IUGG decision in 1967 to meet every 4 years (see Ismail-Zadeh and Joselyn, 2019). At the fifth IUGG general assembly in Lisbon in 1933, it was decided to refer to the IUGG Sections as Associations, and so the Meteorology Section was renamed the International Association of Meteorology (IAM); it was then renamed the International Association of Meteorology and Atmospheric Physics (IAMAP) at the 11th IUGG general assembly in Toronto in 1957. Nearly 4 decades later, recognizing the very important role of other traditional scientific disciplines in atmospheric studies, the name was officially changed to the International Association of Meteorology and Atmospheric Sciences (IAMAS) at the 21st general assembly held in Boulder in 1995. Hereafter in this chapter, the association's current name will be used.

Since its beginning, IAMAS has been led by a president, with administrative and organizational activities directed by a secretary-general nominated by the national committees that are members of IUGG. New officers are elected at each of the IUGG general assemblies to serve from the conclusion of that gathering through the next general assembly. Succinct biographical information and portraits are provided for all 23 presidents in Table 2 and Fig. 3 and for all 12 secretaries-general in Table 3 and Fig. 4. All of the officers have been trained as scientists, but they come from a broad range of disciplines, including geography, meteorology, physics, astronomy and mathematics. Up to the 1970s, many of the officers were employees of the national meteorological services, while since then their primary employment has been by universities and research laboratories.

From the time of its formation, IAMAS has been cooperating with the international meteorological organizations organized by the world's national governments. With the formation of the United Nations, IMO's role was taken over by the World Meteorological Organization (WMO) in 1950 (Davies, 1990). A formal agreement between IUGG and WMO was worked out in 1953 that has governed their respective roles since that time, with WMO taking the leading role in organizing meetings of the international meteorological service organizations and IUGG (through IAMAS) organizing meetings aimed at advancing the science of meteorology. To ensure ongoing cooperation, IUGG has, since signing the agreement, appointed a formal liaison with WMO, often a scientist drawn from IAMAS.

A major undertaking of IUGG and its associations in cooperation with other international unions and entities was sponsorship and organization of the International Geophysical Year (IGY) in 1957–1958. Along with later satellite-based data, data from the expanded observation network established during IGY has made clear that Planet Earth must be considered as an integrated whole. To ensure ongoing cooperation in observations and research, ICSU created the Scientific Committee on Oceanic Research (SCOR) in 1957 and the Scientific Committee on Antarctic Research (SCAR) in 1958 to promote interdisciplinary science on the oceans and Antarctica, respectively. Ever since then, IAMAS has had representation in these organizations, participating in their governance on behalf of IUGG.

Beginning in the 1970s, IAMAS and the other IUGG Associations began holding their own (sometimes joint) Scientific Assemblies in the years between the quadrennial IUGG general assemblies (Table 4). The first such IAMAS Scientific Assembly was convened jointly with the International Association of the Physical Sciences of the Ocean (IAPSO) in Melbourne in 1974. The assembly drew participation from nations on both sides of the “Cold War,” an openness to all that IUGG and its associations now enshrine. Given the geophysical continua of the solid, liquid, and gaseous Earth, atmospheric studies under the umbrella of IAMAS benefitted significantly from the advances in observations and understanding led by a number of its sister associations, primarily involving IAGA (Mandea and Petrosky, 2019), IAPSO (Smythe-Wright et al., 2019), IAHS (Rosbjerg and Rodda, 2019) and IACS (Allison et al., 2019).

The variable climatic conditions of the 1970s and the emerging indications that human activities were starting to influence the climate led to formation of the World Climate Research Programme (WCRP) by ICSU (IUGG's parent organization) and WMO in 1980, with UNESCO's Intergovernmental Oceanographic Commission joining as a sponsor in 1993. The WCRP Joint Scientific Committee (JSC) was formed, drawing members from both the governmental and non-governmental scientific community. The JSC and a sister body under the International Geosphere Biosphere Programme (IGBP) organized a number of major projects, often in cooperation with IUGG and its various components (including IAMAS and its commissions), covering the Earth system from the surface to the stratosphere and the tropics to the poles as well as physical, chemical and biological processes from the hydrologic cycle to cycling of atmospheric pollutants. Over ensuing decades, IAMAS has appointed representatives to participate in both planning meetings and project activities, especially when the area of study has included the atmosphere.

The wide range of topics considered at the Rome general assembly made clear that the scope of important topics encompassed in atmospheric sciences is large. With observation and research efforts intensifying through the 20th century, the number of specialists in each of the particular areas grew, leading to IAMAS adopting an internal structure that would promote focused development and cooperation in each area while still encouraging integration across the study of meteorology and atmospheric sciences.

To accomplish this, IAMAS has, over its history, established 10 scientific commissions (see Table 5). Each commission has a particular scientific focus and its own set of officers and members. In addition to describing the scientific scope of each commission, the following paragraphs list a few of the many scientists from around the world who have been responsible for advancing understanding in each area, generally focusing on those involved in the early to mid-20th century and even before. A good number of these commissions have become so large that they convene their own scientific meetings, typically bringing together hundreds of scientists, most often in years other than those when IUGG general assemblies and IAMAS scientific assemblies are held. In addition to meetings held under IUGG and IAMAS auspices, many of the commissions also arrange to meet jointly with other IUGG associations or are involved with them in related or co-sponsored international scientific programmes. In addition, commission members often serve as representatives to or are on the leadership teams for scientific projects sponsored by other international bodies. A comparison of the leading scientists mentioned in the commission highlights below with the names of officers listed in Tables 2 and 3 reflects the organizing notion of IUGG that its associations have officers drawn from those who can be prominent and knowledgeable spokespersons for the scientific areas encompassed by its commissions.

With respect to the organization of scientific research relating to the Earth system, the year 1919 was one of very significant achievement, setting the stage for very significant advances over the succeeding 100 years and beyond. As World War I ended and a serious flu epidemic waned, the rebirth and expansion of international scientific cooperation to its modern scope began. Observational systems were growing in coverage, and scientific understanding of why changes were occurring expanded. Leading scientists of the time showed exceptional foresight in moving to establish the foundation of the international structure that has carried forward scientific advancement in the century since. While much has been learned, the questions for the decades ahead remain as important and daunting as they were 100 years ago, providing a strong and continuing rationale for IAMAS and its 10 commissions to continue to promote international cooperation and advancement.

The IAMAS focus on advancing scientific understanding of the atmosphere has benefited greatly from both active participation of the world community of atmospheric scientists and also from the advances by the broader geosciences community represented within IUGG. With collective gratitude to all who have served and participated in IAMAS over the past 10 decades, IAMAS welcomes all who would join in ongoing and emerging atmospheric and meteorological research. Further information on IAMAS is available at http://www.iamas.org (last access: 25 January 2019).

The multitude of scientific associations, commissions, and similar groupings within and outside of the parenting International Union of Geodesy and Geophysics may appear confusing at times. It reflects, however, the human endeavour to form various cooperating groups and to categorize phenomena arising from the interrelated and transient continua of the solid, liquid and gaseous compartments of the Earth system. Good (2000) reflected in detail about the evolving geophysical scientific disciplines that together form the union called IUGG. Upon IUGG's centennial, may this commemorative article contribute further to a common memory and tradition into the future about personalities and groupings that have dealt scientifically with atmospheric issues during the past century.