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BAMS State of the Climate 2021

2021

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BAMS State of the Climate 2021 finds that major indicators of climate change, such as sea level or glacier mass balance, all broke the records that were set just one year ago.

Last Updated

26 September 2022

Published on

23 September 2022

By Rob Roebeling and Viju John (EUMETSAT)

Each year the American Meteorological Society (AMS) publishes an annual State of the Climate report in their Bulletin (BAMS). These international, peer-reviewed reports provide an authoritative and comprehensive summary of the Earth's climate of the preceding calendar year, and puts its findings in a historical context. Since the first State of the Climate report in 1991, the reliance on satellite observations has increased from year-to-year. The recent editions analyse variations and trends of the major indicators of climate change. The report relies on contributions from hundreds of authors from more than 60 nations. EUMETSAT's contributions to these reports started with the advent of Metop around 2008 and has gradually increased.

Main findings of report

In 2021, the release of the major long-lived greenhouse gases into Earth’s atmosphere continued to increase. The atmospheric concentrations of these gases, i.e carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), reached levels not seen in the last million years. Also, the annual growth rates of these three gases were also among the highest since instrument records began on the 1950s.

Regardless of the weak-to-moderate La Niña conditions, which generally have a damping effect on global temperatures, the year 2021 was still among the sixth warmest since the mid-1800s. Apart from colder-than-normal annual temperatures in Australia, exceptional warm temperatures were reported in China, Europe, and New Zealand. Record high maximum temperatures were reported round the globe. With as absolute record a maximum temperature of 49.6°C in Canada, breaking the previous record by more than 4°C.

Consistent with the ‘typical’ La Niña pattern, global precipitation amounts over both land and ocean were among the lowest of the past three decades. However, in particular at regional scales, record high extreme precipitation amounts were recorded, for example in China about 200mm/hr and in Italy about 700mm/day. Related to this, the percentage of global land subject to moderate-to-extreme drought conditions continued the sharp increase that began in 2019. In August 2021, the percentage of global land area experiencing moderate or worse drought reached an 80 year peak.

Finally, the report notes that major indicators of climate change, such as sea level, ocean heat content, glacier mass balance, and permafrost all broke the records that were set just one year before.

The above, is a stark reminder that factors leading to a changing climate are determined by time horizons far longer than a single year, and have an inertia that will take a significant effort over a much longer period to halt, much less reverse, current climate trends.

EUMETSAT's contributions

Part of the findings of the 2021 State of the Climate report are based on data from EUMETSAT and the Satellite Application Facilities (SAFs). These can be direct contributions, including observations from sensors onboard EUMETSAT satellites or (multiple) satellite-based data records of Essential Climate Variables (ECVs), such as cloud or water vapour climatologies. Moreover, EUMETSAT contributes, indirectly, by providing sensor data or climatologies of Essential Climate Variables to the reanalyses of the European Centre for Medium-Range Weather Forecasts (ECMWF), Such as, for example, data from Metop's scatterometers (ASCAT), data from Metop's ozone monitoring spectrometer (GOME-2), or data from Metop's GPS Receiver for Atmospheric Sounding (GRAS).

The Earth poles are becoming more cloudy

The impact of changes in cloudiness on Earth's climate can be twofold. Firstly, clouds cool Earth by reflecting incoming solar radiation. Secondly, clouds warm Earth by trapping outgoing terrestrial radiation. Whether the overall effect is one of cooling or warming depends on many factors, including the geographic distribution, height, and opacity of clouds (Bony et al. 2015). In the last two decades global cloudiness remained reasonably stable. However, on a regional scale significant changes in cloudiness occurred.

The year 2021 was among the cloudiest years in the last two decades. Similar to 2020, the above-normal global cloudiness may be associated with the ongoing La Niña event. In general, the mean global cloudiness stayed reasonably stable at about 67%. The year-to-year variations in global cloudiness, as observed from five cloud climatologies, were mostly within 0.5% (Figure 1, left panel). Although global cloudiness seems to lack a distinct trend, regional trends in cloudiness are more obvious. For example, the cloudiness in the Arctic (65° -90° N) and Antarctic (65° -90° S) both show significant increases in the past two decades (Figure 1, right panel).

EUMETSAT's Climate Monitoring Satellite Application Facility (CM SAF) global cloud climatology, CLARA-A2 (see data record references), was used for the cloud analysis of the 2021 State of the Climate report. The CLARA-A2 trends and anomalies agree well with the other cloud climatologies that were analysed (see Figure 1).

Global average cloud fraction anomaly relative to the 2003-2021 reference period for six cloud climatologies. Trends in zonal cloud fraction
Figure 1: (left panel) Global average cloud fraction anomaly relative to the 2003-2021 reference period for six cloud climatologies. (right panel) Trends in zonal cloud fraction (% per decade) over same reference period from the MODIS Aqua C6.1 cloud climatology. (Credit: Mike Foster and Cora Phillips, University of Wisconsin)

Steady increase of atmospheric and upper tropospheric water vapour

Atmospheric total column water vapour (TCWV) plays an important role in the transport of energy. It influences patterns of precipitation and evaporation, and, therefore, the occurrence of drought and floods. Global changes in the total amount of water vapour in our atmosphere are strongly related to global changes in surface and atmospheric temperatures. This is because a warmer atmosphere can hold more moisture (or water vapour). Since the 1980s, the total amount of atmospheric water vapour started to gradually increase, as is unanimously confirmed by reanalyses and satellite-based data (Figure 2).

In 2021, the amounts of atmospheric water vapour, both over land and ocean, were only slightly above the 1981-2020 climatological averages. The prevailing La Niña conditions in 2021 had a cooling effect on surface and atmospheric temperatures, and, therefore, had a lowering effect on the water-holding capacity of Earth's atmosphere.

EUMETSAT indirectly contributes to the analyses of atmospheric water vapour in the State of the Climate report by delivering radio occultation observations from ours and third-party instruments to ECMWF's reanalyses (see data record references).

 Changes in yearly anomalies of atmospheric water vapor, expressed as total colunm water vapor anomalies relative to 1991-2020, from reanalyses (ERA-5, MERRA-2, JRA-55) and satellite-based radio occultation data (GPS-RO)
Figure 2: Changes in yearly anomalies of atmospheric water vapor, expressed as total colunm water vapor anomalies relative to 1991-2020, from reanalyses (ERA-5, MERRA-2, JRA-55) and satellite-based radio occultation data (GPS-RO). Source: State of Climate, 2021.

The amount of water vapour in Earth's middle-upper troposphere — atmospheric layer between about 3-15km above the surface — accounts for a large part of the atmospheric greenhouse effect and is believed to be an important amplifier of climate change (Coleman and Soden 2021). Similar to TCWV, upper tropospheric water vapour has been steadily increasing during the past four decades (Figure 3, lower panel).

In 2021, the relative humidity of upper tropospheric water vapour was slightly below the 1991–2020 average (Figure 3, upper panel). However, in a warming troposphere a zero trend in relative humidity means a positive trend in absolute (or specific) humidity. That the Earth's upper troposphere indeed moistened in the last four decades, is confirmed by a positive trend in the difference between two satellite-based temperatures. Firstly, temperatures at a wavelength mostly sensitive to oxygen warm with time, and secondly, temperatures at a wavelength mostly sensitive to water vapour remain constant with time (Figure 3, lower panel).

EUMETSAT indirectly contributes to the analyses of middle-upper tropospheric water vapour in the State of the Climate report, through the provision of microwave data and High-resolution Infra-Red Sounder (HIRS) data from ours and third-party instruments to ECMWF's reanalyses, (see data record references).

(upper panel) Time series of upper tropospheric humidity anomalies relative to the 1991-2020 climatological mean (%rh) from HIRS (black), Microwave (blue), and ERA5 (purple) datasets. (lower panel) Difference between oxigine sensitive temperature (T2) and water vapor sensitive temperature (T12) observations in the upper troposphere.
Figure 3: (upper panel) Time series of upper tropospheric humidity anomalies relative to the 1991-2020 climatological mean (%rh) from HIRS (black), Microwave (blue), and ERA5 (purple) datasets. (lower panel) Difference between oxygen sensitive temperature (T2) and water vapour sensitive temperature (T12) observations in the upper troposphere. Source: State of Climate, 2021

Stronger winds round Antarctica

The global trend in sea surface wind speed from satellite instruments — such as space-based microwaves and scatterometers — was nearly zero over the period 1991–2020. Still, distinct trends, both positive and negative, are observed at regional scales. In agreement with the findings of previous studies (e.g., Deng et al. 2022 or Zha et al. 2021), winds in the Southern Hemisphere tended to strengthen and shift poleward. The persistent south movement of the wind belt around Antarctica, described by the so-called Southern Annular Mode, is a key climatological phenomenon. It is known to cause warming and drying over Patagonia, and glacier recession in western Antarctica and the Antarctic Peninsula. On the other hand, sea surface winds in the Northern Hemisphere it tend to weaken, for example, in the equatorial and Eastern Atlantic, and Indian oceans (Figure 4, left panel).

In 2021, the mean sea surface wind speeds over the global oceans, as observed from different satellite data and reanalyses, were slightly above the 1991-2020 average. Largely in line with the regional trends in wind speed, the most prominent positive anomalies in 2021 were recorded in the Southern oceans, and negative anomalies in the equatorial and Northern Atlantic oceans (Figure 4, right panel).

EUMETSAT indirectly contributes to the analyses of sea surface winds in the State of the Climate report, through the provision microwave and scatterometer data, as well as through the provision of scatterometer winds from Ocean and Sea Ice SAF (OSI SAF) to ECMWF's reanalyses (see data record references).

(left panel) Ocean wind speed trends from ERA5 reanalysis and satellite microwave and scatterometer instruments for the period 1988–2021. (right panel) 2021 ocean wind speed anomaly from ERA5 reanalysis and satellite microwave and scatterometer instruments relative to the 1991-2020 climatological mean
Figure 4:  (left panel) Ocean wind speed trends from ERA5 reanalysis and satellite microwave and scatterometer instruments for the period 1988–2021. (right panel) 2021 ocean wind speed anomaly from ERA5 reanalysis and satellite microwave and scatterometer instruments relative to the 1991-2020 climatological mean. Source: State of Climate, 2021

The trends in upper air wind speed at a height of about 1.5km above the surface (850hPa) are consistent to those observed at the sea surface. Here, a distinct trend in global upper air wind speeds has been absent in the past three decades (Figure 5). Similarly, at regional scales both large positive trends, as for example over the Southern Ocean close to Antarctica, and large negative trends, as for example over the eastern Indian Ocean, manifest.

In 2021, the global mean upper air wind speed was slightly above the long term (1991–2020) climatological mean (Figure 5). In the Southern Hemisphere, the wind belt of strong westerly winds contracted towards Antarctica, and was among the strongest since the 1980s.

EUMETSAT indirectly contributes to the analyses of upper air wind speeds in the State of the Climate report, through the provision of atmospheric motion vector winds from ours and NOAA satellites to ECMWF's reanalyses (see data record references). Atmospheric motion vector winds are derived by tracing movements of clouds or water vapour fields from frequent satellite observations.

Global annual winds speed anomalies at 850 hpa relative to 1991-2020 climatological mean of four reanalyses
Figure 5: Global annual winds speed anomalies at 850hpa relative to 1991-2020 climatological mean of four reanalyses. Source: State of Climate, 2021

Ozone hole recovers slowly

Stratospheric ozone protects Earth’s biosphere from harmful ultraviolet radiation. The abundant usage of anthropogenic ozone-depleting substances caused thinning of the layer of stratospheric ozone. It was only after the phase out of these substances, as mandated by the Montreal Protocol in the late 1980s, that the loss of stratospheric ozone gradually started to slowdown, and even recovered in some regions. It is especially in the very upper stratosphere at 2hPa (about 40km above the surface) where the clearest signs of ozone recovery are evident. Lower in the stratosphere, at 50hPa (about 20km above the surface), ozone concentration hardly changed during the past three decades.

In 2021, the global mean total column ozone concentration remained close to the level where it has been since the 1990s. The regional distribution of anomalies (Figure 6) shows that, in 2021, concentrations were mostly lower than the decadal mean (1998–2008). Only round two bands, of which one near latitude 20° N and one near latitude 20° S, the concentrations were higher than the decadal mean. The observed patterns were attributed to dominant weather regimes in 2021.

EUMETSAT contributes to the analyses of stratospheric ozone in the State of the Climate report through the provision of GOME-2 data from the Metop satellites and, indirectly, through the total ozone column data record jointly provided by Deutsches Zentrum für Luft- und Raumfahrt (DLR) and the Atmospheric Composition SAF (AC SAF) for Multi sensor reanalysis (see data record references).

GOME-2C total column ozone anomalies relative to the 1998–2008 mean in DU
Figure 6: GOME-2C total column ozone anomalies relative to the 1998–2008 mean in DU. Source: State of Climate, 2021

Earth's ocean levels continues to rise

Earth's ocean levels have been rising almost uninterrupted over the past four decades. The prime driver of sea level rise is the inflow of water from melting glaciers and ice sheets — of which the glaciers on Greenland and Antarctica are the most important. An important secondary driver of sea level rise is the absorption of heat by the oceans. As this heat is absorbed, ocean water warms and expands. The latter is responsible for one-third of global sea level rise, whereas, the inflow of melt water is responsible for two-third of sea level rise (see Ocean observations from space confirm disruption of Earth's energy balance).

In 2021, the average global mean sea level reached a new high, with current levels almost 10cm above those of 1993. The amounts of sea level rise vary regionally. Sea levels rose most in the western Pacific and the eastern Indian Ocean, and least in the north-eastern Pacific and parts of the south-central Indian Ocean (Figure 7).

EUMETSAT contributes to the analyses of sea level variability in the State of the Climate report through the provision of measurements of satellite altimetry instruments on Sentinel-3A and Jason-3, that the Copernicus Marine and Environment Monitoring Service uses for the multi-mission sea level product.

Annual average sea level anomaly during 2021 relative to average sea level at each location during 1993–2021.  Altimetry data were obtained from the gridded, multi-mission product
Figure 7: Annual average sea level anomaly during 2021 relative to average sea level at each location during 1993–2021. Altimetry data were obtained from the gridded, multi-mission product maintained by the Copernicus Marine and Environment Monitoring Service. Source: State of Climate, 2021

References

Latest versions of data records used in State of the Climate 2021

Satellite-based climate data record of cloud, albedo and solar radiation, derived from data of AVHRR on NOAA over the period 1982-2019, from the Climate Monitoring Satellite Application Facility (CM SAF) that is cited as:
Karlsson, Karl-Göran; Anttila, Kati; Trentmann, Jörg; Stengel, Martin; Solodovnik, Irina; Meirink, Jan Fokke; Devasthale, Abhay; Kothe, Steffen; Jääskeläinen, Emmihenna; Sedlar, Joseph; Benas, Nikos; van Zadelhoff, Gerd-Jan; Stein, Diana; Finkensieper, Stephan; Håkansson, Nina; Hollmann, Rainer; Kaiser, Johannes; Werscheck, Martin (2020): CLARA-A2.1: CM SAF cLoud, Albedo and surface RAdiation dataset from AVHRR data — Edition 2.1, Satellite Application Facility on Climate Monitoring, DOI:10.5676/EUM_SAF_CM/CLARA_AVHRR/V002_01, https://doi.org/10.5676/EUM_SAF_CM/CLARA_AVHRR/V002_01 (accessed on 05/09/2022)

Satellite-based interim data record of cloud, albedo and solar radiation, derived from data of AVHRR on NOAA over the period 2019-2021, from the Climate Monitoring Satellite Application Facility (CM SAF) that is cited as:
Karlsson, Karl-Göran; Riihelä, Aku; Trentmann, Jörg; Stengel, Martin; Meirink, Jan Fokke; Solodovnik, Irina; Devasthale, Abhay; Manninen, Terhikki; Jääskeläinen, Emmihenna; Anttila, Kati; Kallio-Myers, Vilvi; Benas, Nikos; Selbach, Nathalie; Stein, Diana; Kaiser, Johannes; Hollmann, Rainer (2021): ICDR AVHRR — based on CLARA-A2 methods, Satellite Application Facility on Climate Monitoring, https://wui.cmsaf.eu/safira/action/viewICDRDetails?acronym=CLARA_AVHRR_V002_ICDR (accessed on 05/09/2022)

Satellite-based data record of Atmospheric Motion Vectors, derived from Meteosat First Generation MVIRI data and Meteosat Second Generation SEVIRI data, over the period 1981-2019, that is cited with DOI:10.15770/EUM_SEC_CLM_0020 (see http://doi.org/10.15770/EUM_SEC_CLM_0020, accessed on 2022-09-07)

A satellite based data record of Polar Atmospheric Motion Vectors, derived from data of AVHRR on Metop, covering 2008-2017, that is cited with DOI:10.15770/EUM_SEC_CLM_0037, (see http://doi.org/10.15770/EUM_SEC_CLM_0037 (accessed on 07/09/2022))

Satellite-based data record of Polar Atmospheric Motion Vectors, derived from data of AVHRR on the TIROS-N, NOAA and Metop satellites, covering 1979-2019, that is cited with DOI:10.15770/EUM_SEC_CLM_0056 (see http://doi.org/10.15770/EUM_SEC_CLM_0056 (accessed on 07/09/2022))

Satellite-based data record of radio occultation bending angle profiles from measurements of the CHAMP, COSMIC, GRACE and Metop satellites, covering 2001-2020, that is cited with DOI:10.15770/EUM_SEC_CLM_0030 (see http://doi.org/10.15770/EUM_SEC_CLM_0030), DOI:10.15770/EUM_SEC_CLM_0031 (see http://doi.org/10.15770/EUM_SEC_CLM_0031), DOI:10.15770/EUM_SEC_CLM_0032 (see http://doi.org/10.15770/EUM_SEC_CLM_0032), and DOI:10.15770/EUM_SEC_CLM_0051 (see http://doi.org/10.15770/EUM_SEC_CLM_0051) (accessed on 07/09/2022)

Satellite-based data record of ozone total column density, derived from GOME-2 data on Metop, covering 2007-2017, that is cited as:
AC SAF (2017): GOME-2 O3 Total Column Density Data Record Release 2 - Metop, EUMETSAT SAF on Atmospheric Composition Monitoring, DOI: 10.15770/EUM_SAF_O3M_0009. http://dx.doi.org/10.15770/EUM_SAF_O3M_0009 (accessed on 07/09/2022)

Satellite-based data record of brightness temperatures obtained from the American, European, and Chinese microwave humidity sounders (see http://doi.org/10.15770/EUM_SEC_CLM_0035), covering 1975-2019, that is cited with DOI:10.15770/EUM_SEC_CLM_0035 (see https://doi.org/10.15770/EUM_SEC_CLM_0035) and DOI:10.15770/EUM_SEC_CLM_0036 (see https://doi.org/10.15770/EUM_SEC_CLM_0036) (accessed on 07/09/2022)

Satellite-based data record of backscatter data from ASCAT on the Metop satellites, covering 2007-2020, that is cited with DOI:10.15770/EUM_SEC_CLM_0042 (see http://doi.org/10.15770/EUM_SEC_CLM_0042) (accessed on 07/09/2022)

Satellite-based data record of backscattered radiances in visible part of the spectrum (240nm–790nm), derived from data of GOME-2 on Metop, covering the period 2007-2020, that is cited as:
EUMETSAT (2022): GOME-2 Level 1B Fundamental Data Record Release 3 - Metop-A and -B, European Organisation for the Exploitation of Meteorological Satellites, DOI: 10.15770/EUM_SEC_CLM_0039. http://doi.org/10.15770/EUM_SEC_CLM_0039 (accessed on 07/09/2022)

Daily satellite-based data record of sea level observations, derived from different altimetry missions, such as EUMETSAT's Jason and Sentinel 3 missions, covering the period 1993-date. The data are provided by the Copernicus Climate Change Service (C3S) and is made available via the Copernicus Data Store at https://cds.climate.copernicus.eu/cdsapp#!/dataset/satellite-sea-level-global?tab=overview (accessed on 07/09/2022).

Articles

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Bony, S., and Coauthors, 2015: Clouds, circulation and climate sensitivity. Nat. Geosci., 8, 261–268, https://doi.org/10.1038/ngeo2398

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Zha, J., and Coauthors, 2021: Projected changes in global terrestrial near-surface wind speed in 1.5°C–4.0°C global warming levels. Environ. Res. Lett., 16, 114016, https://doi.org/10.1088/1748-9326/ac2fdd