365 Days of Climate Awareness 176 – 2021 State of the World Climate

2021 World Climate Data

• Global atmospheric CO₂ concentration: 416.45 ppm, +2.21 ppm from 2020 (preliminary: Mauna Loa only)
• Surface air temperature anomaly: +0.84°C/1.51°F, 6^th all-time 1880-2021
• Precipitation 22.5 (0.4 in) mm below 1961-1990 global average 1033 mm (40.7 in)
• Global mean sea level 62.53 mm above 1993-2008 average, +5.98 mm from 2020 (preliminary: satellite data only)
• Antarctic ozone hole: max. area 24.8 million km²; minimum O₃ 92 DU (Dobson Units)
• ENSO: La Niña
• NAO: Mosty negative (cooler in southeastern US and northern Europe; warmer in northeastern Canada and southern Europe), then variable

Larger Version

Global Conditions

• Above-average temperatures:  South America; Africa; Europe; Asia
• Above-average precipitation: Central Europe; Scandinavia; the Baltic states; northern Russia; Mongolia; northern China; Oceania; southwestern and southeastern Australia
• Below-average precipitation: Southern South America; southern and eastern Europe; central Siberia; southern China; Iran; Pakistan; south central Australia

2021 featured a fairly consistent La Niña. ENSO correlates closely to global mean temperature, largely due to the ocean surface but also because of its atmospheric effects. A plot of global mean temperature anomalies overlaid with ENSO status makes this correlation very clear. Despite the clear upward trend in overall planetary temperature, the main noise in the signal—the overlaid, shorter-term cycle—is the oscillation between El Niño and La Niña. So it is hardly surprising that 2021 was the hottest La Niña year on record.

La Niña episodes act to store more heat in the ocean, as the higher winds increase circulation, both horizontally and vertically. The upwelling on the eastern edge of the Pacific basin is matched by downwelling toward the west, as warm water is driven further down into the Pacific, spreading heat energy further throughout the climate system. El Niño events, with their reduced equatorial winds, lead to an increasingly stratified Pacific Ocean, with heat gathered near the surface, marked by an increasingly sharp and deep thermocline boundary with the cooler, deeper water. La Niña does the opposite, and drives the surface warmth further down into the water column.

Larger Version

There is low confidence among climate scientists about identifying or predicting any kind of trend in ENSO toward increasing frequency or strength of El Niño, neutral, or La Niña conditions. Recent studies of the last 7-10,000 years indicate that ENSO variations are becoming stronger, a possible sign of the increasing energy level and volatility of the world climate system. It must be stressed, however, that no firm consensus on this topic has been reached.

Tomorrow: recent decadal climate trends.

Be brave, and be well.