Syukuro Manabe was awarded the Nobel Prize in Physics in 2021 for his work on climate modeling. The Prize recognizes an exceptional career that pioneered a new area of the scientific enterprise revealing the power of numerical simulations and methods for advancing scientific discovery and producing new knowledge. Manabe contributed decisively to the creation of the modern scientific discipline of climate science through numerical modeling, stressing clarity of ideas and simplicity of approach. He described in no uncertain terms the role of greenhouse gases in the atmosphere and the impact of changes in the radiation balance of the atmosphere caused by the anthropogenic increase of such gases, and he revealed the role of water vapor in the greenhouse effect. He also understood the importance of including all the components of the climate system (the oceans, sea ice, and land surface) to reach a comprehensive treatment of the mechanisms of climate in a general circulation model, paving the way to the modern earth system models and the establishment of climate modeling as a leading scientific discipline.
Sharon E. Nicholson
Classic paradigms describing meteorological phenomena and climate have changed dramatically over the last half-century. This is particularly true for the continent of Africa. Our understanding of its climate is today very different from that which prevailed as recently as the 1960s or 1970s. This article traces the development of relevant paradigms in five broad areas: climate and climate classification, tropical atmospheric circulation, tropical rain-bearing systems, climatic variability and change, and land surface processes and climate. One example is the definition of climate. Originally viewed as simple statistical averages, it is now recognized as an environmental variable with global linkages, multiple timescales of variability, and strong controls via earth surface processes. As a result of numerous field experiments, our understanding of tropical rainfall has morphed from the belief in the domination by local thunderstorms to recognition of vast systems on regional to global scales. Our understanding of the interrelationships with land surface processes has also changed markedly. The simple Charney hypothesis concerning albedo change and the related concept of desertification have given way to a broader view of land–atmosphere interaction. In summary, there has been a major evolution in the way we understand climate, climatic variability, tropical rainfall regimes and rain-bearing systems, and potential human impacts on African climate. Each of these areas has evolved in complexity and understanding, a result of an explosive growth in research and the availability of such investigative tools as satellites, computers, and numerical models.
Elisabeth Lipiatou and Anastasios Kentarchos
Although the first European Union Framework Programme (FP) for research and technological development was created in 1984, it was the second FP (FP2) in 1987 that devoted resources to climatological research for the first time. The start of FP2 coincided with the establishment of the Intergovernmental Panel on Climate Change in 1988, aimed at providing a comprehensive assessment on the state of knowledge of the science of climate change. FP-funded research was not an end in itself but a means for the European Union (EU) to achieve common objectives based on the principle of cross-border research cooperation and coordination to reduce fragmentation and effectively tackle common challenges. Since 1987, climate science has been present in all nine FPs (as of 2023) following an evolutionary process as goals, priority areas, and financial and implementation instruments have constantly changed to adapt to new needs. A research- and technology-oriented Europe was gradually created including in the area of climate science. There has historically been a strong intrinsic link, there has been a strong, intrinsic link between research and environmental and climate policies. Climate science under the FPs, focusing initially on oceans, the carbon cycle, and atmospheric processes, has increased tremendously both in scope and scale, encompassing a broad range of areas over time, such as climate modeling, polar research, ocean acidification, regional seas and oceans, impacts and adaptation, decarbonization pathways, socioeconomic analyses, sustainability, observations, and climate services. The creation and evolution of the EU’s FPs has played a critical role in establishing Europe’s leading position on climate science by means of promoting excellence, increasing the relevance of climate research for policymaking, and building long-lasting communities and platforms across Europe and beyond as international cooperation has been a key feature of the FPs. No other group of countries collaborates on climate science at such scale. Due to their inherited long-term planning and cross-national nature, the FPs have provided a stable framework for advancing climate science by incentivizing scientists and institutions with diverse expertise to work together, creating the necessary critical mass to tackle the increasing complex and interdisciplinary nature of climate science, rationalizing resource allocation, and setting norms and standards for scientific collaboration. It is hard to imagine in retrospect how a similar level of impact could have been achieved solely at a national level. Looking ahead and capitalizing on the rich experience and lessons learned since the 1980s, important challenges and opportunities need to be addressed. These include critical gaps in knowledge, even higher integration of disciplines, use of new technologies and artificial intelligence for state-of-the-art data analysis and modeling, capturing interlinkages with sustainable development goals, better coordination between national and EU agendas, higher mobility of researchers and ideas from across Europe and beyond, and stronger interactions between scientists and nonscientific entities (public authorities, the private sector, financial institutions, and civil society) in order to better communicate climate science and proactively translate new knowledge into actionable plans.
Saji N. Hameed
Discovered at the very end of the 20th century, the Indian Ocean Dipole (IOD) is a mode of natural climate variability that arises out of coupled ocean–atmosphere interaction in the Indian Ocean. It is associated with some of the largest changes of ocean–atmosphere state over the equatorial Indian Ocean on interannual time scales. IOD variability is prominent during the boreal summer and fall seasons, with its maximum intensity developing at the end of the boreal-fall season. Between the peaks of its negative and positive phases, IOD manifests a markedly zonal see-saw in anomalous sea surface temperature (SST) and rainfall—leading, in its positive phase, to a pronounced cooling of the eastern equatorial Indian Ocean, and a moderate warming of the western and central equatorial Indian Ocean; this is accompanied by deficit rainfall over the eastern Indian Ocean and surplus rainfall over the western Indian Ocean. Changes in midtropospheric heating accompanying the rainfall anomalies drive wind anomalies that anomalously lift the thermocline in the equatorial eastern Indian Ocean and anomalously deepen them in the central Indian Ocean. The thermocline anomalies further modulate coastal and open-ocean upwelling, thereby influencing biological productivity and fish catches across the Indian Ocean. The hydrometeorological anomalies that accompany IOD exacerbate forest fires in Indonesia and Australia and bring floods and infectious diseases to equatorial East Africa. The coupled ocean–atmosphere instability that is responsible for generating and sustaining IOD develops on a mean state that is strongly modulated by the seasonal cycle of the Austral-Asian monsoon; this setting gives the IOD its unique character and dynamics, including a strong phase-lock to the seasonal cycle. While IOD operates independently of the El Niño and Southern Oscillation (ENSO), the proximity between the Indian and Pacific Oceans, and the existence of oceanic and atmospheric pathways, facilitate mutual interactions between these tropical climate modes.
Timothy M. Shanahan
West Africa is among the most populated regions of the world, and it is predicted to continue to have one of the fastest growing populations in the first half of the 21st century. More than 35% of its GDP comes from agricultural production, and a large fraction of the population faces chronic hunger and malnutrition. Its dependence on rainfed agriculture is compounded by extreme variations in rainfall, including both droughts and floods, which appear to have become more frequent. As a result, it is considered a region highly vulnerable to future climate changes. At the same time, CMIP5 model projections for the next century show a large spread in precipitation estimates for West Africa, making it impossible to predict even the direction of future precipitation changes for this region. To improve predictions of future changes in the climate of West Africa, a better understanding of past changes, and their causes, is needed. Long climate and vegetation reconstructions, extending back to 5−8 Ma, demonstrate that changes in the climate of West Africa are paced by variations in the Earth’s orbit, and point to a direct influence of changes in low-latitude seasonal insolation on monsoon strength. However, the controls on West African precipitation reflect the influence of a complex set of forcing mechanisms, which can differ regionally in their importance, especially when insolation forcing is weak. During glacial intervals, when insolation changes are muted, millennial-scale dry events occur across North Africa in response to reorganizations of the Atlantic circulation associated with high-latitude climate changes. On centennial timescales, a similar response is evident, with cold conditions during the Little Ice Age associated with a weaker monsoon, and warm conditions during the Medieval Climate Anomaly associated with wetter conditions. Land surface properties play an important role in enhancing changes in the monsoon through positive feedback. In some cases, such as the mid-Holocene, the feedback led to abrupt changes in the monsoon, but the response is complex and spatially heterogeneous. Despite advances made in recent years, our understanding of West African monsoon variability remains limited by the dearth of continuous, high- resolution, and quantitative proxy reconstructions, particularly from terrestrial sites.
Anjuli S. Bamzai
In the years following the Second World War, the U.S. government played a prominent role in the support of basic scientific research. The National Science Foundation (NSF) was created in 1950 with the primary mission of supporting fundamental science and engineering, excluding medical sciences. Over the years, the NSF has operated from the “bottom up,” keeping close track of research around the United States and the world while maintaining constant contact with the research community to identify ever-moving horizons of inquiry. In the 1950s the field of meteorology was something of a poor cousin to the other branches of science; forecasting was considered more of trade than a discipline founded on sound theoretical foundations. Realizing the importance of the field to both the economy and national security, the NSF leadership made a concerted effort to enhance understanding of the global atmospheric circulation. The National Center for Atmospheric Research (NCAR) was established to complement ongoing research efforts in academic institutions; it has played a pivotal role in providing observational and modeling tools to the emerging cadre of researchers in the disciplines of meteorology and atmospheric sciences. As understanding of the predictability of the coupled atmosphere-ocean system grew, the field of climate science emerged as a natural outgrowth of meteorology, oceanography, and atmospheric sciences. The NSF played a leading role in the implementation of major international programs such as the International Geophysical Year (IGY), the Global Weather Experiment, the World Ocean Circulation Experiment (WOCE) and Tropical Ocean Global Atmosphere (TOGA). Through these programs, understanding of the coupled climate system comprising atmosphere, ocean, land, ice-sheet, and sea ice greatly improved. Consistent with its mission, the NSF supported projects that advanced fundamental knowledge of forcing and feedbacks in the coupled atmosphere-ocean-land system. Research projects have included theoretical, observational, and modeling studies of the following: the general circulation of the stratosphere and troposphere; the processes that govern climate; the causes of climate variability and change; methods of predicting climate variations; climate predictability; development and testing of parameterization of physical processes; numerical methods for use in large-scale climate models; the assembly and analysis of instrumental and/or modeled climate data; data assimilation studies; and the development and use of climate models to diagnose and simulate climate variability and change. Climate scientists work together on an array of topics spanning time scales from the seasonal to the centennial. The NSF also supports research on the natural evolution of the earth’s climate on geological time scales with the goal of providing a baseline for present variability and future trends. The development of paleoclimate data sets has resulted in longer term data for evaluation of model simulations, analogous to the evaluation using instrumental observations. This has enabled scientists to create transformative syntheses of paleoclimate data and modeling outcomes in order to understand the response of the longer-term and higher magnitude variability of the climate system that is observed in the geological records. The NSF will continue to address emerging issues in climate and earth-system science through balanced investments in transformative ideas, enabling infrastructure and major facilities to be developed.
Zhu Kezhen (1890–1974), also known as Chu Coching, was a Harvard-educated meteorologist who worked in the field of climate sciences in China from 1918 to 1974. He was highly regarded under vastly different political regimes. His concerns regarding the development of observatory networks, educational practices, and the establishment of research topics reflect the development of the field in China, which only began at the very end of the 19th century. Zhu Kezhen was influenced by the meteorological and climate knowledge imparted to him by his academic teachers in the United States and appropriated Ellsworth Huntington’s ideas on climate determinism, which shaped some of his fundamental concerns. One of his main achievements was to make use of a wide array of observational and other data in order to contribute to the “localization” of climate science. In fact, employing data culled from traditional sources and making use of and expanding the phenological knowledge of traditional Chinese rural society allowed him to approach climate science in a way that was not easily possible in the West. Zhu’s research into historical climate change in China embodied many aspects of his approach to the localization of science in China, but changes in the international scientific network (from an American-European to a Soviet-dominated network) and the political turmoil in the People’s Republic of China greatly impaired his work. Zhu’s research remains highly influential and has exerted considerable influence on environmental and climate history.