State of the climate in 2018

In 2018, the dominant greenhouse gases released into Earth’s atmosphere—carbon dioxide, methane, and nitrous oxide—continued their increase. The annual global average carbon dioxide concentration at Earth’s surface was 407.4 ± 0.1 ppm, the highest in the modern instrumental record and in ice core records dating back 800 000 years. Combined, greenhouse gases and several halogenated gases contribute just over 3 W m−2 to radiative forcing and represent a nearly 43% increase since 1990. Carbon dioxide is responsible for about 65% of this radiative forcing. With a weak La Niña in early 2018 transitioning to a weak El Niño by the year’s end, the global surface (land and ocean) temperature was the fourth highest on record, with only 2015 through 2017 being warmer. Several European countries reported record high annual temperatures. There were also more high, and fewer low, temperature extremes than in nearly all of the 68-year extremes record. Madagascar recorded a record daily temperature of 40.5°C in Morondava in March, while South Korea set its record high of 41.0°C in August in Hongcheon. Nawabshah, Pakistan, recorded its highest temperature of 50.2°C, which may be a new daily world record for April. Globally, the annual lower troposphere temperature was third to seventh highest, depending on the dataset analyzed. The lower stratospheric temperature was approximately fifth lowest. The 2018 Arctic land surface temperature was 1.2°C above the 1981–2010 average, tying for third highest in the 118-year record, following 2016 and 2017. June’s Arctic snow cover extent was almost half of what it was 35 years ago. Across Greenland, however, regional summer temperatures were generally below or near average. Additionally, a satellite survey of 47 glaciers in Greenland indicated a net increase in area for the first time since records began in 1999. Increasing permafrost temperatures were reported at most observation sites in the Arctic, with the overall increase of 0.1°–0.2°C between 2017 and 2018 being comparable to the highest rate of warming ever observed in the region. On 17 March, Arctic sea ice extent marked the second smallest annual maximum in the 38-year record, larger than only 2017. The minimum extent in 2018 was reached on 19 September and again on 23 September, tying 2008 and 2010 for the sixth lowest extent on record. The 23 September date tied 1997 as the latest sea ice minimum date on record. First-year ice now dominates the ice cover, comprising 77% of the March 2018 ice pack compared to 55% during the 1980s. Because thinner, younger ice is more vulnerable to melting out in summer, this shift in sea ice age has contributed to the decreasing trend in minimum ice extent. Regionally, Bering Sea ice extent was at record lows for almost the entire 2017/18 ice season. For the Antarctic continent as a whole, 2018 was warmer than average. On the highest points of the Antarctic Plateau, the automatic weather station Relay (74°S) broke or tied six monthly temperature records throughout the year, with August breaking its record by nearly 8°C. However, cool conditions in the western Bellingshausen Sea and Amundsen Sea sector contributed to a low melt season overall for 2017/18. High SSTs contributed to low summer sea ice extent in the Ross and Weddell Seas in 2018, underpinning the second lowest Antarctic summer minimum sea ice extent on record. Despite conducive conditions for its formation, the ozone hole at its maximum extent in September was near the 2000–18 mean, likely due to an ongoing slow decline in stratospheric chlorine monoxide concentration. Across the oceans, globally averaged SST decreased slightly since the record El Niño year of 2016 but was still far above the climatological mean. On average, SST is increasing at a rate of 0.10° ± 0.01°C decade−1 since 1950. The warming appeared largest in the tropical Indian Ocean and smallest in the North Pacific. The deeper ocean continues to warm year after year. For the seventh consecutive year, global annual mean sea level became the highest in the 26-year record, rising to 81 mm above the 1993 average. As anticipated in a warming climate, the hydrological cycle over the ocean is accelerating: dry regions are becoming drier and wet regions rainier. Closer to the equator, 95 named tropical storms were observed during 2018, well above the 1981–2010 average of 82. Eleven tropical cyclones reached Saffir–Simpson scale Category 5 intensity. North Atlantic Major Hurricane Michael’s landfall intensity of 140 kt was the fourth strongest for any continental U.S. hurricane landfall in the 168-year record. Michael caused more than 30 fatalities and $25 billion (U.S. dollars) in damages. In the western North Pacific, Super Typhoon Mangkhut led to 160 fatalities and$6 billion (U.S. dollars) in damages across the Philippines, Hong Kong, Macau, mainland China, Guam, and the Northern Mariana Islands. Tropical Storm Son-Tinh was responsible for 170 fatalities in Vietnam and Laos. Nearly all the islands of Micronesia experienced at least moderate impacts from various tropical cyclones. Across land, many areas around the globe received copious precipitation, notable at different time scales. Rodrigues and Réunion Island near southern Africa each reported their third wettest year on record. In Hawaii, 1262 mm precipitation at Waipā Gardens (Kauai) on 14–15 April set a new U.S. record for 24-h precipitation. In Brazil, the city of Belo Horizonte received nearly 75 mm of rain in just 20 minutes, nearly half its monthly average. Globally, fire activity during 2018 was the lowest since the start of the record in 1997, with a combined burned area of about 500 million hectares. This reinforced the long-term downward trend in fire emissions driven by changes in land use in frequently burning savannas. However, wildfires burned 3.5 million hectares across the United States, well above the 2000–10 average of 2.7 million hectares. Combined, U.S. wildfire damages for the 2017 and 2018 wildfire seasons exceeded $40 billion (U.S. dollars)

Korrektur von strukturellen Inhomogenitäten im globalen ESA CCI Soil-Moisture-Datensatz (von multiplen Satelliten)

Abweichender Titel nach Übersetzung der Verfasserin/des VerfassersESA CCI Soil Moisture ist ein mehr als 40 Jahre umfassender Datensatz, der den global Bodenwassergehalt beschreibt. Es werden darin Messungen unterschiedlicher aktiver und passiver, satellitengestützterMikrowellen-Fernerkundungssystemen vereint. Unterschiede in den Sensoreigenschaften (wie Wellenlänge oder Polarisation der gemessenen Strahlung) der kombinierten Messsysteme können zu Inhomogenitäten ("Sprüngen") im finalen Datensatz führen, die weiterführende Studien negative beein ussen können. Diese Arbeit befasst sich mit der Untersuchung von drei Methodiken zur Reduzierung von Inhomogenitäten im ESA CCI SM Datensatz. Ihr Potential zur Verbesserung der Homogenität inerhalb des Datensatzes wird ebenso wie ihre Auswirkungen auf den Datensatz im Bezug auf Validierungsmetriken untersucht. Der Ein uss von Inhomogenitäten und deren Korrektur auf Langzeitstudien wird Anhand von Trends im Bodenfeuchtesignal untersucht. Wir kommen zum Schluss, dass alle drei Methoden die Anzahl der detektierbaren Inhomogenitäten im Datensatz reduzieren, wobei Unterschiede im Potential zur Korrektur von Inhomogenit äten in der Varianz der Messungen festgestellt werden. Validierung der korrigierten Messungen zeigt nur geringe änderungen im Hinblick auf (relative) Fehlermetriken. änderungen in den Bodenfeuchtetrends aufgrund der Korrektur werden in einigen Gebieten festgestellt. Die Korrektur von Inhomogenitäten verbessert global betrachtet die Qualität des Datensatzes, wobei der das Klima beschreibenden Anteil des Signals weitestgehend erhalten bleibt. Eine der drei Methodiken ("Quantile Category Matching") wird gegenüber den anderen als bevorzuziehend identifiziert.The ESA CCI Soil Moisture COMBINED product is a more than 40 year long data record on global soil moisture for climate studies and applications. It merges soil moisture observations derived from multiple active and passive satellite remote sensing instruments in the microwave domain. Differences in sensor characteristics (such as frequency or polarisation) can cause structural breaks in the product, which are not completely removed during the merging process. These artificially caused discontinuities can adversely affect studies using the long-term data set as they make changes in the observations unrepresentative of long-term changes in reality. Here we compare three adjustment methods in terms of reducing the number of detected breaks in the soil moisture record. We investigate their impact on the data with multiple validation metrics. Their potential (negative) influence is examined by comparing trends in the data before and after homogenisation. We find that all three presented methods can reduce the number of detected breaks in ESA CCI SM. Differences between the methods mainly concern their ability to handle inhomogeneities in variance. Evaluation of the corrected data shows limited impact of homogenisation in terms of quantitative validation metrics. Changes in soil moisture trends due to removing breaks are found in some areas. We find that break correction overall improves the already rather homogeneous data set while preserving its climate describing characteristics. Quantile Category Matching is identified as the preferred method in terms of correcting breaks in ESA CCI SM.5

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Homogenisation of structural breaks in the global ESA CCI Soil Moisture multi-satellite climate data record

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ESA CCI and C3S Soil Moisture: latest product updates and climate assessments

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Homogenization of structural breaks in the global ESA CCI multi-satellite climate data record

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L-Band Soil Moisture Retrievals Using Microwave Based Temperature and Filtering. Towards Model-Independent Climate Data Records

The CCI Soil Moisture dataset (CCI SM) is the most extensive climate data record of satellite soil moisture to date. To maximize its function as a climate benchmark, both long-term consistency and (model-) independence are high priorities. Two unique L-band missions integrated into the CCI SM are SMOS and SMAP. However, they lack the high-frequency microwave sensors needed to determine the effective temperature and snow/frozen flagging, and therefore use input from (varying) land surface models. In this study, the impact of replacing this model input by temperature and filtering based on passive microwave observations is evaluated. This is derived from an inter-calibrated dataset (ICTB) based on six passive microwave sensors. Generally, this leads to an expected increase in revisit time, which goes up by about 0.5 days (~15% loss). Only the boreal regions have an increased coverage due to more accurate freeze/thaw detection. The boreal regions become wetter with an increased dynamic range, while the tropics are dryer with decreased dynamics. Other regions show only small differences. The skill was evaluated against ERA5-Land and in situ observations. The average correlation against ERA5-Land increased by 0.05 for SMAP ascending/descending and SMOS ascending, whereas SMOS descending decreased by 0.01. For in situ sensors, the difference is less pronounced, with only a significant change in correlation of 0.04 for SM SMOS ascending. The results indicate that the use of microwave-based input for temperature and filtering is a viable and preferred alternative to the use of land surface models in soil moisture climate data records from passive microwave sensors

Microwave remote sensing for agricultural drought monitoring: Recent developments and challenges

Agricultural droughts are extreme events which are often a result of interplays between multiple hydro-meteorological processes. Therefore, assessing drought occurrence, extent, duration and intensity is complex and requires the combined use of multiple variables, such as temperature, rainfall, soil moisture (SM) and vegetation state. The benefit of using information on SM and vegetation state is that they integrate information on precipitation, temperature and evapotranspiration, making them direct indicators of plant available water and vegetation productivity. Microwave remote sensing enables the retrieval of both SM and vegetation information, and satellite-based SM and vegetation products are available operationally and free of charge on a regional or global scale and daily basis. As a result, microwave remote sensing products play an increasingly important role in drought monitoring applications. Here, we provide an overview of recent developments in using microwave remote sensing for large-scale agricultural drought monitoring. We focus on the intricacy of monitoring the complex process of drought development using multiple variables. First, we give a brief introduction on fundamental concepts of microwave remote sensing together with an overview of recent research, development and applications of drought indicators derived from microwave-based satellite SM and vegetation observations. This is followed by a more detailed overview of the current research gaps and challenges in combining microwave-based SM and vegetation measurements with hydro-meteorological data sets. The potential of using microwave remote sensing for drought monitoring is demonstrated through a case study over Senegal using multiple satellite- and model-based data sets on rainfall, SM, vegetation and combinations thereof. The case study demonstrates the added-value of microwave-based SM and vegetation observations for drought monitoring applications. Finally, we provide an outlook on potential developments and opportunities.Mathematical Geodesy and Positionin

Global Climate

In 2021, both social and economic activities began to return towards the levels preceding the COVID-19 pandemic for some parts of the globe, with others still experiencing restrictions. Meanwhile, the climate has continued to respond to the ongoing increase in greenhouse gases and resulting warming. La Niña, a phenomenon which tends to depress global temperatures while changing rainfall patterns in many regions, prevailed for all but two months of the year. Despite this, 2021 was one of the six-warmest years on record as measured by global mean surface temperature with an anomaly of between +0.21° and +0.28°C above the 1991–2020 climatology. Lake surface temperatures were their highest on record during 2021. The number of warm days over land also reached a new record high. Exceptional heat waves struck the Pacific Coast of North America, leading to a new Canadian maximum temperature of 49.6°C at Lytton, British Columbia, on 29 June, breaking the previous national record by over 4°C. In Death Valley, California, the peak temperature reached 54.4°C on 9 July, equaling the temperature measured in 2020, and the highest temperature recorded anywhere on the globe since at least the 1930s. Over the Mediterranean, a provisional new European record of 48.8°C was set in Sicily on 11 August. In the atmosphere, the annual mean tropospheric temperature was among the 10 highest on record, while the stratosphere continued to cool. While La Niña was present except for June and July, likely influencing Australia’s coolest year since 2012 and wettest since 2016, other modes of variability played important roles. A negative Indian Ocean dipole event became established during July, associated with a warmer east and cooler west Indian Ocean. Northern Hemisphere winters were affected by a negative phase of the North Atlantic Oscillation at both the beginning and end of 2021. In the Southern Hemisphere, a very strong positive Southern Annular Mode (also known as the Antarctic Oscillation) contributed to New Zealand’s record warm year and to very cold temperatures over Antarctica. Land surface winds continued a slow reversal from the multi-decadal stilling, and over the ocean wind speeds were at their highest in almost a decade. La Niña conditions had a clear influence on the regional patterns of many hydrological variables. Surface specific humidity and total column water vapor over land and ocean were higher than average in almost all datasets. Relative humidity over land reached record or near-record low saturation depending on the dataset, but with mixed signals over the ocean. Satellite measurements showed that 2021 was the third cloudiest in the 19-year record. The story for precipitation was mixed, with just below-average mean precipitation falling over land and below-average mean precipitation falling over the ocean, while extreme precipitation was generally more frequent, but less intense, than average. Differences between means and extremes can be due to several factors, including using different indices, observing periods, climatological base reference periods, and levels of spatial completeness. The sharp increase in global drought area that began in mid-2019 continued in 2021, reaching a peak in August with 32% of global land area experiencing moderate or worse drought, and declining slightly thereafter. Arctic permafrost temperatures continued to rise, reaching record values at many sites, and the thickness of the layer which seasonally thaws and freezes also increased over 2020 values in a number of regions. It was the 34th-consecutive year of mass balance loss for alpine glaciers in mountainous regions, with glaciers on average 25 m thinner than in the late 1970s. And the duration of lake ice in the Northern Hemisphere was the fourth lowest in situ record dating back to 1991. The atmospheric concentrations of the major long-lived greenhouse gases, CO2, CH4, and N2O, all reached levels not seen in at least the last million years and grew at near-record rates in 2021. La Niña conditions did not appear to have any appreciable impact on their growth rates. The growth rate for CH4, of 17 ppb yr−1, was similar to that for 2020 and set yet another record, although the causes for this post-2019 acceleration are unknown presently. Overall, CO2 growth continues to dominate the increase in global radiative forcing, which increased from 3.19 to 3.23 W m−2 (watts per square meter) during the year. In 2021, stratospheric ozone did not exhibit large negative anomalies, especially near the poles, unlike 2020, where large ozone depletions appeared, mainly from dynamical effects. The positive impact of reductions in emissions of ozone depleting substances can be seen most clearly in the upper stratosphere, where such dynamical effects are less pronounced. It was the fourth-lowest fire year since global records began in 2003, though extreme regional fire activity was again seen in North America and also in Siberia; as in 2020, the effects of wildfires in these two regions led to locally large regional positive anomalies in tropospheric aerosol and carbon monoxide abundance. Vegetation is responding to the higher global mean temperatures, with the satellite-derived measures for the Northern Hemisphere for 2021 rated among the earliest starts of the growing season and the latest end of the season on record. The first bloom date for cherry trees in Kyoto, Japan, broke a 600-year record set in 1409. This year we welcome a sidebar on the global distribution of lightning, which has been recently declared an essential climate variable (ECV) by the Global Climate Observing System (GCOS). Time series and anomaly maps from many of the variables described in this chapter can be found in Plates 1.1 and 2.1. As with other chapters, many of the sections have moved from the previous 1981–2010 to the new 1991–2020 climatological reference period, in line with WMO recommendations (see Chapter 1). This is not possible for all datasets, as it is dependent on their length of record or legacy processing methods. While anomalies from the new climatology period are not so easily comparable with previous editions of this report, they more clearly highlight deviations from more recent conditions