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In 2019, the dominant greenhouse gases released into Earth’s atmosphere continued to increase. The annual global average carbon dioxide concentration at Earth’s surface was 409.8 ± 0.1 ppm, an increase of 2.5 ± 0.1 ppm over 2018, and the highest in the modern instrumental record and in ice core records dating back 800 000 years. Combined, greenhouse gases and several halogenated gases contributed 3.14 W m−2 to radiative forcing, representing a 45% increase since 1990. Carbon dioxide is responsible for about 65% of this radiative forcing. The annual net global uptake of ∼2.4 billion metric tons of carbon dioxide by oceans was the highest in the record dating to 1982 and 33% higher than the 1997–2017 average. A weak El Niño at the beginning of 2019 transitioned to ENSO-neutral conditions by mid-year. Even so, the annual global surface temperature across land and oceans was still among the three highest in records dating to the mid- to late 1800s. July 2019 was Earth’s hottest month on record. Well over a dozen countries across Africa, Europe, Asia, Australia, and the Caribbean reported record high annual temperatures. In North America, Alaska experienced its warmest year on record, while the high northern latitudes that encompass the Arctic were second warmest, behind only 2016. Stations in several countries, including Vietnam, the Netherlands, Belgium, Luxembourg, France, and the United Kingdom, set new all-time daily high temperature records for their nations. Australia set a new nationally averaged daily maximum temperature record of 41.9°C on 18 December, breaking the previous record set in 2013 by 1.6°C. Daily temperatures surpassed 40°C for the first time in Belgium and the Netherlands. Lake temperatures increased on average across the globe in 2019; observed lakes in the Northern Hemisphere were covered in ice seven days fewer than the 1981–2010 average, according to phenological indicators. Over land, the growing season was an average of eight days longer than the 2000–10 average in the NH. Above Earth’s surface, the annual lower troposphere temperature was third highest to record high, and the lower stratosphere temperature was third lowest to record low, depending on the dataset analyzed. Middle- and upper-stratospheric temperatures were lowest on record since satellite records began in 1979. In September, Antarctica experienced a dramatic upper-atmosphere warming event that led to the smallest ozone hole since the early 1980s. Below-average Antarctic sea ice extent persisted throughout 2019, continuing a trend that began in September 2016. Net sea ice extent was below the 1981–2010 average for all days of the year, and January and June each set a new low monthly mean sea ice extent record. The Antarctic ice sheet continued to lose mass, with the highest rates of loss occurring in West Antarctica and Wilkes Land, East Antarctica. Across the cryosphere, alpine glaciers continued to lose mass for the 32nd consecutive year. Permafrost temperatures in the European Alps were slightly below the record temperatures measured in 2015, while record high permafrost temperatures were observed at a majority of the observation sites across the high northern latitudes. For the first time in the observational record at 26 sites in interior Alaska and the Seward Peninsula, the active layer did not freeze completely, a result of long-term permafrost warming and back-to-back relatively mild and snowy winters. In March, when Arctic sea ice reached its annual maximum extent, thin, first-year ice comprised ∼77% of all ice, compared to about 55% in the 1980s. In September, the minimum sea ice extent tied for the second smallest extent in the 41-year satellite record. In the Bering Sea, increasing ocean temperatures and reduced sea ice—which was the lowest on record there for the second consecutive winter—are leading to shifts in fish distributions within some of the most valuable fisheries in the world. Larger and more abundant boreal species, as opposed to smaller and less abundant Arctic species, dominated a large portion of the Arctic shelf in 2018 and 2019. During the 2019 melt season, the extent and magnitude of ice loss over the Greenland ice sheet rivaled 2012, the previous year of record ice loss. Melting of glaciers and ice sheets, along with warming oceans, account for the trend in rising global mean sea level. In 2019, global mean sea level set a new record for the eighth consecutive year, reaching 87.6 mm above the 1993 average when satellite measurements began, with an annual average increase of 6.1 mm from 2018. Ocean heat content measured to 700 m depth was record high, and the globally averaged sea surface temperature was the second highest on record, surpassed only by the record El Niño year of 2016. In October, the Indian Ocean dipole exhibited its greatest magnitude since 1997, associated with dramatic upper ocean warming in the western Indian Ocean basin. While ENSO conditions during 2019 appeared to have limited impacts, many climate events were influenced by the strong positive IOD, which contributed to a large rainfall deficit from the eastern Indian Ocean to the South Pacific Ocean east of Australia. Record heat and dryness in Australia intensified drought conditions already in place following below-average rainfall in 2017 and 2018, leading to severe impacts during late austral spring and summer, including catastrophic wildfires. Smoke from these wildfires, along with the volcanic eruptions of Raikoke (Russia) and Ulawun (Papua New Guinea), helped load the stratosphere with aerosol levels unprecedented since the post-Mt. Pinatubo era of the early 1990s. Indonesia also suffered severe drought and extreme wildfires toward the end of 2019; no rainfall was observed in the East Sumba District of the East Nusa Tenggara Province for 263 days. Conversely, the positive IOD also contributed to excess rainfall over the Horn of Africa from August through December, resulting in widespread flooding across East Africa. Elsewhere, India experienced one of its heaviest summer monsoon rains since 1995 despite a delayed and suppressed monsoon during June. In the United States, rapid snowmelt in the spring, as well as heavy and frequent precipitation in the first half of the year, contributed to extensive flooding in the Midwest throughout spring and summer, notably the Mississippi and Missouri basins. Dry conditions persisted over large parts of western South Africa, in some locations having continued for approximately seven years. Antecedent dry conditions and extreme summer heat waves pushed most of Europe into extreme drought. Due in part to precipitation deficits during December 2018 to January 2019—the peak of the rainy season—wildfires scorched vast areas of the southern Amazonian forests in Bolivia, Brazil, and Peru, as well as in northern Paraguay, later in 2019. Millions of trees and animals perished, with some local extinctions reported. In Siberia, fire activity during the summer was both strong and farther north than usual. This led to a new record of 27 teragrams (1012 g) of carbon emitted from fires in the Arctic, which was more than twice as high than in any preceding year. Closer to the equator, 96 named tropical storms were observed during the Northern and Southern Hemisphere storm seasons, well above the 1981–2010 average of 82. Five tropical cyclones reached Saffir–Simpson scale Category 5 intensity. In the North Atlantic basin, Hurricane Dorian caused unprecedented and tremendous devastation, with over 70 fatalities and damages totaling $3.4 billion (U.S. dollars) in The Bahamas. Tropical Cyclones Idai and Kenneth severely impacted southeastern Africa in March and April, respectively. Idai resulted in total damages of at least $2.2 billion (U.S. dollars), the costliest storm on record for the South Indian Ocean basin, as well as the deadliest with over 1200 fatalities across Mozambique, Zimbabwe, Malawi, and Madagascar.

The 15th Education Symposium, held as part of the 86th American Meteorological Society (AMS) Annual Meeting, addressed the scope of education and outreach efforts within atmospheric and related sciences. The first presentation outlined the critical need for reform, noting that the recent assessment \"Trends in international mathematics and science study\" indicates that U.S. students are not performing well in math and science, and that many science teachers, especially Earth science teachers, have not had opportunities to develop deep content knowledge or engage in research. After a formal poster-viewing break, five presentations focused on student learning and the use of technology in the classroom, including the students' responses to the use of an interactive personal computer (PC) Tablet by instructors in the meteorology classroom; the use of an active-learning quiz in Introduction to Meteorology, using the \"Who Wants to be a Millionaire\" approach; tools for teaching climate change science, including a pre- and postcourse questionnaire; an exercise on creating and distributing a survey focused on students' understanding of relative humidity; and educational tools to enhance a student's ability to go from coursework to applications using meteorological instrumentation.

International Arctic Systems for Observing the Atmosphere (IASOA) activities and partnerships were initiated as a part of the 2007–09 International Polar Year (IPY) and are expected to continue for many decades as a legacy program. The IASOA focus is on coordinating intensive measurements of the Arctic atmosphere collected in the United States, Canada, Russia, Norway, Finland, and Greenland to create synthesis science that leads to an understanding of why and not just how the Arctic atmosphere is evolving. The IASOA premise is that there are limitations with Arctic modeling and satellite observations that can only be addressed with boots-on-the-ground, in situ observations and that the potential of combining individual station and network measurements into an integrated observing system is tremendous. The IASOA vision is that by further integrating with other network observing programs focusing on hydrology, glaciology, oceanography, terrestrial, and biological systems it will be possible to understand the mechanisms of the entire Arctic system, perhaps well enough for humans to mitigate undesirable variations and adapt to inevitable change.

Climate observations are needed to address a large range of important societal issues including sea level rise, droughts, floods, extreme heat events, food security, and freshwater availability in the coming decades. Past, targeted investments in specific climate questions have resulted in tremendous improvements in issues important to human health, security, and infrastructure. However, the current climate observing system was not planned in a comprehensive, focused manner required to adequately address the full range of climate needs. A potential approach to planning the observing system of the future is presented in this article. First, this article proposes that priority be given to the most critical needs as identified within the World Climate Research Program as Grand Challenges. These currently include seven important topics: melting ice and global consequences; clouds, circulation and climate sensitivity; carbon feedbacks in the climate system; understanding and predicting weather and climate extremes; water for the food baskets of the world; regional sea‐level change and coastal impacts; and near‐term climate prediction. For each Grand Challenge, observations are needed for long‐term monitoring, process studies and forecasting capabilities. Second, objective evaluations of proposed observing systems, including satellites, ground‐based and in situ observations as well as potentially new, unidentified observational approaches, can quantify the ability to address these climate priorities. And third, investments in effective climate observations will be economically important as they will offer a magnified return on investment that justifies a far greater development of observations to serve society's needs. Key Points A significantly expanded climate observing system could address major science questions and meet important societal needs Careful independent testing can evaluate whether proposed systems can address critical observing needs Future investments in climate observations offer large societal benefits and economic return on investments Plain Language Summary The current climate observing system cannot address the range of important scientific and societally important climate issues. A significantly expanded climate observing system could address major science questions and meet important societal needs. Careful independent testing can evaluate whether proposed systems can address critical observing needs. Future investments in climate observations offer large societal benefits and economic return on investments.

This article includes a rationale for the American Chemical Society's new text (Chemistry in Context), as well as a brief history, and description of the content and pedagogy.