This article documents events, research findings, scientific and technological advances, and human actions to measure, predict, mitigate, and adapt to the effects of global warming and climate change—during the year 2021.
Summaries
26 February: The United Nations Synthesis Report on Nationally Determined Contributions under the Paris Agreement stated that "estimated reductions referred to in paragraphs (on greenhouse gas emissions) fall far short of what is required, demonstrating the need for Parties to further strengthen their mitigation commitments under the Paris Agreement". 21 June: the World Meteorological Organization wrote that "2021 is a make-or-break year for climate action, with the window to prevent the worst impacts of climate change—which include ever more frequent more intense droughts, floods and storms—closing rapidly." 28 July: a follow-on to the 2019 World Scientists' Warning of a Climate Emergency noted "an unprecedented surge in climate-related disasters since 2019" and stated there is "mounting evidence that we are nearing or have already crossed tipping points associated with critical parts of the Earth system". 6 September: editors from over 200 health journals published a joint editorial stating "The science is unequivocal; a global increase of 1.5 °C above the pre-industrial average and the continued loss of biodiversity risk catastrophic harm to health that will be impossible to reverse.... The greatest threat to global public health is the continued failure of world leaders to keep the global temperature rise below 1.5 °C and to restore nature." 30 September: UN Secretary-General António Guterres stated that "time is running out. Irreversible climate tipping points lie alarmingly close." He called for more ambition as current NDCs will lead to a rise of 2.7 °C, saying that "all leaders must recognize that we are in the middle of a climate emergency".
Measurements and statistics
25 January: a review article published in The Cryosphere reported that Earth lost 28 trillion tonnes of ice between 1994 and 2017, 68% being from atmospheric melting and 32% by oceanic melting. The rate of ice loss rose 57% since the 1990s–from 0.8 to 1.2 trillion tonnes per year–raising global sea level 34.6 ±3.1 mm in that time period. 9 February: a study published in Environmental Research concluded that airborne fine particulate matter (PM2.5) caused by burning fossil fuels causes 8.7 million premature deaths annually, including China (2.4 million), India (2.5 million) and parts of eastern US, Europe and Southeast Asia. 16 February: study results published in the PNAS (study's time period: 1990–2018) reported widespread advances and lengthening of pollen seasons (up to 20 days) and increases in pollen concentrations (up to 21%) across North America, with human forcing of the climate system contributing about 50% of the trend in pollen seasons and about 8% of the trend in pollen concentrations. Atlantic meridional overturning circulation (AMOC): 25 February: a Nature Geoscience article reported an "unprecedented" (since AD 400) decline in the twentieth century of the Atlantic meridional overturning circulation (AMOC), which is now in its weakest state in more than 1,000 years. The AMOC redistributes heat on the planet and has a major impact on climate. In particular, weakness in the AMOC, which includes the Florida Current and the Gulf Stream, counteracts its moderating effect on the climate in Europe. 5 August: a study published in Nature Climate Change presented "spatially consistent empirical evidence that, in the course of the last century, the AMOC may have evolved from relatively stable conditions to a point close to a critical transition". February: measurements from Mauna Loa Observatory showed that, for the first time, atmospheric levels reached 417 parts per million (ppm), a concentration 50% higher than the 278ppm pre-industrial level. March: Global Energy Monitor published a study on coal mine methane emissions which found that hundreds of newly proposed coal mines could emit 13.5 million tonnes of methane annually.Ryan Driskell Tate,Coal Mine Methane On the Brink, March 2021 8 March: a study published in Nature Climate Change—studying the combined effects of average global sea level rise and natural and human-induced subsidence—estimated that subsiding coastal locations may locally experience up to four times more relative sea level rise than could be attributed to global sea level rise alone. 17 March: a study by the International Federation of Red Cross and Red Crescent Societies estimated that, globally between September 2020 and February 2021, 12.5 million people were displaced by adverse impacts of climate change, the annual average exceeding 20 million. 17 March: a study published in Nature estimated that trawling's disturbance of carbon stored in sea beds can re-mineralize sedimentary carbon into amounts equivalent to 15–20% of the atmospheric absorbed by the ocean each year, and comparable to that of terrestrial farming. 18 March: a study accepted for publication in Environmental Research Letters estimated that the severity of heatwave and drought impacts on crop production in Europe roughly tripled over the preceding 50 years, from –2.2 (1964–1990) to -7.3% (1991–2015). 1 April: a study published in Nature Climate Change estimated that anthropogenic climate change has reduced global agricultural total factor productivity by about 21% since 1961, and 26–34% in warmer regions such as Africa, Latin America and the Caribbean. 7 April: NOAA reported carbon dioxide levels were higher than at anytime in the past 3.6 million years, in the Mid-Pliocene Warm Period when sea level was about 24 mm (78 ft) higher than today and the average temperature was about 4 °C (7 °F) higher than in pre-industrial times. NOAA's redefinition of "average" and "normal": April: NOAA's Climate Prediction Center (CPC) states it will use 1991–2020 as the new 30-year period of record, with "average" numbers of named Atlantic storms rising from 12 to 14, hurricanes from 6 to 7, and major hurricanes remaining at 3; Eastern Pacific and Central Pacific numbers remain unchanged over 1981–2010. May: NOAA's NCEI supersedes weather and climate data from 1981–2010 with data from 1991–2020 to change its designation of "Climate Normal", resulting in fewer days being characterized as having "above normal" temperature. 28 April: a study published in Nature attributed 21±3% of the observed sea-level rise from 2000–2019 to melting glaciers (267±16 gigatonnes per year), and identified a mass loss acceleration of 48±16 gigatonnes per year per decade. 11 May: a study published in Nature Communications estimated that land use change affected 32% of the global land area from 1960 to 2019, about four times greater than previously estimated. 20 May: The Arctic Monitoring and Assessment Programme reported that, from 1971 to 2019, the annually averaged Arctic near-surface air temperature increased by 3.1 °C, three times faster than the global average. 21 May: a study published in Geophysical Research Letters reported that, despite greater raw warming in high latitudes, the tropics have greater normalized warming and actually experienced more record-breaking heat events from 1960 to 2019. 24 May: a study published in Nature Geoscience reported mercury in Greenland ice sheet meltwater being two orders of magnitude higher than from Arctic rivers, and, accounting for about 10% of the estimated global riverine flux, estimated it to be globally significant. 31 May: a study published in Nature Climate Change concluded that 37% of warm-season heat-related deaths from 1991 to 2018 can be attributed to anthropogenic climate change and that increased mortality is evident on every continent. 4 June: a study published in Science Advances concluded that previous estimates of emissions caused by human cultivation of peatlands from 1750 to 2018 should be increased by 18% to account for emissions from cultivated northern peatlands in calculating the carbon budget. 15 June: a study accepted for publication in Geophysical Research Letters reported that satellite and in situ observations independently show an approximate doubling of Earth's Energy Imbalance (EEI) from mid-2005 to mid-2019. 28 July: a study published in Nature Communications revealed a significant positive global energy imbalance based on satellite observations from 2001 to 2020, and concluded that there is less than 1% probability that this imbalance can be explained by natural internal variability of the climate system.
31 August: the WMO published an Atlas of Mortality and Economic Losses from Weather, Climate and Water Extremes (1970–2019), indicating that the number of disasters has increased by a factor of five, driven by climate change, more extreme weather and improved reporting; but because of improved early warnings and disaster management the number of deaths decreased almost three-fold. 1 September: a study published in Nature found that since 2001, fires in the Amazon rainforest had potentially impacted ranges of 77.3–85.2% of threatened species in the region, reducing the biodiversity that contributes to the ecological and climatic stability of the Amazon Basin. 12 October: a study published in the Proceedings of the NAS estimated a nearly 200% increase in urban heat extremes among 13,115 urban areas from 1983 to 2016. October: The Global Coral Reef Monitoring Network's Status of Coral Reefs of the World reported that "between 2009 and 2018, there was a progressive loss amounting to 14% of the coral from the world's coral reefs, which is more than all the coral currently living on Australia's coral reefs". 30 March 2022: Ember's Global Electricity Review reported that in 2021, wind and solar power reached a record 10% of global electricity, with clean power being 38% of supply, more than coal's 36%. However, demand growth rebounded, leading to a record rise in coal power and emissions. 7 April 2022: NOAA reported an annual increase in global atmospheric methane of 17 parts per billion (ppb) in 2021—averaging 1,895.7 ppb in that year—the largest annual increase recorded since systematic measurements began in 1983. The increase during 2020 was 15.3 ppb, itself a record increase.
Natural events and phenomena 7 February: a rock-ice avalanche in the Chamoli district in the Indian Himalayan Mountains killed dozens and left hundreds missing. The death count grew to 204, with 27 million cubic meters of rock and ice collapsing. March: a Science Brief review of >90 peer-reviewed scientific articles reported consensus that ocean warming from human-induced climate change is likely fueling more powerful tropical cyclones with increased precipitation rates (through enhanced atmospheric moisture), the increased power and rising sea levels amplifying flooding. Models project that some regions will experience increases in rapid intensification, a poleward migration of the latitude of maximum intensity or a slowing of the forward motion of the storms. Most climate model studies project the annual number of tropical cyclones to decrease or remain approximately the same.
5 March: an article published in Science concluded that the Atlantic Multidecadal Oscillation is not an internal multidecadal (40- to 60-year) oscillation distinct from climate noise, but is instead a manifestation of competing time-varying effects of anthropogenic greenhouse gases and sulfate aerosols. 11 March: a review article published in Frontiers in Forests and Global Change concluded that warming from non- agents (especially and ) in the Amazon basin largely offsets—and most likely exceeds—the climate change mitigating effect of the region's uptake.