Rapid surge in global warming mainly due to reduced planetary albedo – positive feedback loop

By Rob | December 9, 2024 |

Image: Albedo is the word to describe the amount sunlight that bounces, or reflects, off of the Earth. The concept of albedo is a very important one in discussions of Earth’s climate, because it relates to how much heat is absorbed by various parts of the Earth. Earth’s albedo is influenced by the physical properties of the planet’s various surfaces. Some surfaces, such as ice and snow, reflect more of the sunlight and absorb less heat than do surfaces like oceans and forests. However, the physical properties of Earth’s surfaces can change, both naturally and due to human activities. To protect Earth and its inhabitants from global warming, there may be ways we can engineer Earth’s albedo so that more of the sun’s heat is reflected away from our planet, but these theories require more research. from What Is Albedo and What Does It Have to Do With Global Warming?

December 5, 2024

Source:
Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research
Summary:
Rising sea levels, melting glaciers, heatwaves at sea — 2023 set a number of alarming new records. The global mean temperature also rose to nearly 1.5 degrees above the preindustrial level, another record. Seeking to identify the causes of this sudden rise has proven a challenge for researchers. After all, factoring in the effects of anthropogenic influences like the accumulation of greenhouse gases in the atmosphere, of the weather phenomenon El Nino, and of natural events like volcanic eruptions, can account for a major portion of the warming. But doing so still leaves a gap of roughly 0.2 degrees Celsius, which has never been satisfactorily explained. A team puts forward a possible explanation for the rise in global mean temperature: our planet has become less reflective because certain types of clouds have declined.
  1. Helge F. Goessling, Thomas Rackow, Thomas Jung. Recent global temperature surge intensified by record-low planetary albedo. Science, 2024; DOI: 10.1126/science.adq7280
FULL STORY

Rising sea levels, melting glaciers, heatwaves at sea — 2023 set a number of alarming new records. The global mean temperature also rose to nearly 1.5 degrees above the preindustrial level, another record. Seeking to identify the causes of this sudden rise has proven a challenge for researchers. After all, factoring in the effects of anthropogenic influences like the accumulation of greenhouse gases in the atmosphere, of the weather phenomenon El Niño, and of natural events like volcanic eruptions, can account for a major portion of the warming. But doing so still leaves a gap of roughly 0.2 degrees Celsius, which has never been satisfactorily explained. A team led by the Alfred Wegener Institute puts forward a possible explanation for the rise in global mean temperature: our planet has become less reflective because certain types of clouds have declined.

“In addition to the influence of El Niño and the expected long-term warming from anthropogenic greenhouse gases, several other factors have already been discussed that could have contributed to the surprisingly high global mean temperatures since 2023,” says Dr Helge Goessling, main author of the study from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI): e.g. increased solar activity, large amounts of water vapour from a volcanic eruption, or fewer aerosol particles in the atmosphere. But if all these factors are combined, there is still 0.2 degrees Celsius of warming with no readily apparent cause.

“The 0.2-degree-Celsius ‘explanation gap’ for 2023 is currently one of the most intensely discussed questions in climate research,” says Helge Goessling. In an effort to close that gap, climate modellers from the AWI and the European Centre for Medium-Range Weather Forecasts (ECMWF) took a closer look at satellite data from NASA, as well as the ECMWF’s own reanalysis data, in which a range of observational data is combined with a complex weather model. In some cases, the data goes back to 1940, permitting a detailed analysis of how the global energy budget and cloud cover at different altitudes have evolved.

“What caught our eye was that, in both the NASA and ECMWF datasets, 2023 stood out as the year with the lowest planetary albedo,” says co-author Dr Thomas Rackow from the ECMWF. Planetary albedo describes the percentage of incoming solar radiation that is reflected back into space after all interactions with the atmosphere and the surface of the Earth. “We had already observed a slight decline in recent years. The data indicates that in 2023, the planetary albedo may have been at its lowest since at least 1940.” This would worsen global warming and could explain the ‘missing’ 0.2 degrees Celsius. But what caused this near-record drop in planetary albedo?

Decline in lower-altitude clouds reduces Earth’s albedo

The albedo of the surface of the Earth has been in decline since the 1970s — due in part to the decline in Arctic snow and sea ice, which also means fewer white areas to reflect back sunlight. Since 2016, this has been exacerbated by sea-ice decline in the Antarctic. “However, our analysis of the datasets shows that the decline in surface albedo in the polar regions only accounts for roughly 15 percent of the most recent decline in planetary albedo,” Helge Goessling explains. And albedo has also dropped markedly elsewhere. In order to calculate the potential effects of this reduced albedo, the researchers applied an established energy budget model capable of mimicking the temperature response of complex climate models. What they found: without the reduced albedo since December 2020, the mean temperature in 2023 would have been approximately 0.23 degrees Celsius lower.

One trend appears to have significantly affected the reduced planetary albedo: the decline in low-altitude clouds in the northern mid-latitudes and the tropics. In this regard, the Atlantic particularly stands out, i.e., exactly the same region where the most unusual temperature records were observed in 2023. “It’s conspicuous that the eastern North Atlantic, which is one of the main drivers of the latest jump in global mean temperature, was characterised by a substantial decline in low-altitude clouds not just in 2023, but also — like almost all of the Atlantic — in the past ten years.” The data shows that the cloud cover at low altitudes has declined, while declining only slightly, if at all, at moderate and high altitudes.

The fact that mainly low clouds and not higher-altitude clouds are responsible for the reduced albedo has important consequences. Clouds at all altitudes reflect sunlight, producing a cooling effect. But clouds in high, cold atmospheric layers also produce a warming effect because they keep the warmth emitted from the surface in the atmosphere. “Essentially it’s the same effect as greenhouse gases,” says Helge Goessling. But lower clouds don’t have the same effect. “If there are fewer low clouds, we only lose the cooling effect, making things warmer.”

But why are there fewer low clouds? Lower concentrations of anthropogenic aerosols in the atmosphere, especially due to stricter regulations on marine fuel, are likely a contributing factor. As condensation nuclei, aerosols play an essential part in cloud formation, while also reflecting sunlight themselves. In addition, natural fluctuations and ocean feedbacks may have contributed. Yet Helge Goessling considers it unlikely that these factors alone suffice and suggests a third mechanism: global warming itself is reducing the number of low clouds. “If a large part of the decline in albedo is indeed due to feedbacks between global warming and low clouds, as some climate models indicate, we should expect rather intense warming in the future,” he stresses. “We could see global long-term climate warming exceeding 1.5 degrees Celsius sooner than expected to date. The remaining carbon budgets connected to the limits defined in the Paris Agreement would have to be reduced accordingly, and the need to implement measures to adapt to the effects of future weather extremes would become even more urgent.”

References and Notes
1. Iwakiri, T., Imada, Y., Takaya, Y., Kataoka, T., Tatebe, H., & Watanabe, M. (2023). Triple-
dip La Niña in 2020–23: North Pacific atmosphere drives 2nd year La Niña. Geophysical
Research Letters, 50, e2023GL105763. https://doi.org/10.1029/2023GL105763
2. Copernicus Climate Change Service (C3S) (2024): European State of the Climate 2023,
Summary: https://doi.org/10.24381/bs9v-8c66
3. Schmidt, G., Climate models can’t explain 2023’s huge heat anomaly — we could be in
uncharted territory, Nature 627, 467 (2024), https://doi.org/10.1038/d41586-024-00816-z
4. Rackow, T., Danilov, S., Goessling, H.F. et al. Delayed Antarctic sea-ice decline in high-
resolution climate change simulations. Nat Commun 13, 637 (2022).
https://doi.org/10.1038/s41467-022-28259-y
5. Kuhlbrodt, T., R. Swaminathan, P. Ceppi, and T. Wilder, 2024: A Glimpse into the Future:
The 2023 Ocean Temperature and Sea Ice Extremes in the Context of Longer-Term Climate
Change. Bull. Amer. Meteor. Soc., 105, E474–E485, https://doi.org/10.1175/BAMS-D-23-
0209.1
6. Roach, L.A., Meier, W.N. Sea ice in 2023. Nat Rev Earth Environ 5, 235–237 (2024).
https://doi.org/10.1038/s43017-024-00542-0
7. Kopp, G. (2016). Magnitudes and timescales of total solar irradiance variability. J. Space
Weather Space Clim. 6, A30. doi:10.1051/swsc/2016025.
8. Mark Robin Schoeberl, Yi Wang, Ghassan Taha, et al. (2024). Evolution of the Climate
Forcing During the Two Years after the Hunga Tonga-Hunga Ha’apai Eruption. ESS Open
Archive . April 12, 2024. DOI: 10.22541/essoar.171288896.63010190/v1
9. Hansen et al. (2024), Global warming in the pipeline, Oxford Open Climate Change, Volume
3, Issue 1, 2023, kgad008, https://doi.org/10.1093/oxfclm/kgad008
10. Manshausen, P., Watson-Parris, D., Christensen, M.W. et al. (2022). Invisible ship tracks
show large cloud sensitivity to aerosol. Nature 610, 101–106 https://doi.org/10.1038/s41586-
022-05122-0
11. Hodnebrog, Ø., Myhre, G., Jouan, C. et al. Recent reductions in aerosol emissions have
increased Earth’s energy imbalance. Commun Earth Environ 5, 166 (2024).
https://doi.org/10.1038/s43247-024-01324-8
12. Loeb, N. G., and Coauthors (2018). Clouds and the Earth’s Radiant Energy System (CERES)
Energy Balanced and Filled (EBAF) Top-of-Atmosphere (TOA) Edition-4.0 Data Product. J.
Climate, 31, 895–918, https://doi.org/10.1175/JCLI-D-17-0208.1
13. Minnis P et al (2021). CERES MODIS cloud product retrievals for edition 4—Part I:
algorithm changes. IEEE Trans Geosci Remote Sens 59:2744–2780.
https://doi.org/10.1109/TGRS.2020.3008866
14. Hersbach, H., et al. (2020). The ERA5 global reanalysis. Quarterly Journal of the Royal
Meteorological Society, 146(730), 1999-2049. https://doi.org/10.1002/qj.3803
15. Bell et al. (2021), The ERA5 global reanalysis: Preliminary extension to 1950,
https://rmets.onlinelibrary.wiley.com/doi/full/10.1002/qj.4174
12
16. Loeb, N.G., Ham, SH., Allan, R.P. et al. Observational Assessment of Changes in Earth’s
Energy Imbalance Since 2000. Surv Geophys (2024). https://doi.org/10.1007/s10712-024-
09838-8
17. Song, H., Choi, Y.-S., Kang, H. (2024). Global change in cloud radiative effect revealed in
CERES observations. Research Square. Retrieved from
https://www.researchsquare.com/article/rs-3781529/v1
18. Loeb, N. G., Johnson, G. C., Thorsen, T. J., Lyman, J. M., Rose, F. G., & Kato, S. (2021).
Satellite and ocean data reveal marked increase in Earth’s heating rate. Geophysical Research
Letters, 48, e2021GL093047. https://doi.org/10.1029/2021GL093047
19. Donohoe, A., Armour, K. C., Pendergrass, A. G., & Battisti, D. S. (2014). Shortwave and
longwave radiative contributions to global warming under increasing CO2. Proceedings of
the National Academy of Sciences, 111(47), 16700-16705.
https://doi.org/10.1073/pnas.1412190111
20. He, Y., Wang, K., Zhou, C., & Wild, M. (2018). A revisit of global dimming and brightening
based on the sunshine duration. Geophysical Research Letters, 45, 4281–4289.
https://doi.org/10.1029/2018GL077424
21. Kato, S. (2009). Interannual Variability of the Global Radiation Budget. J. Climate, 22,
4893–4907, https://doi.org/10.1175/2009JCLI2795.1
22. Radley, C., S. Fueglistaler, and L. Donner (2014). Cloud and Radiative Balance Changes in
Response to ENSO in Observations and Models. J. Climate, 27, 3100–3113,
https://doi.org/10.1175/JCLI-D-13-00338.1
23. Stephens, G. L., D. O’Brien, P. J. Webster, P. Pilewski, S. Kato, and J. Li (2015), The albedo
of Earth. Rev. Geophys., 53, 141–163. doi: 10.1002/2014RG000449
24. Timmermann, A., An, SI., Kug, JS. et al. El Niño–Southern Oscillation complexity. Nature
559, 535–545 (2018). https://doi.org/10.1038/s41586-018-0252-6
25. Huang, B., and Coauthors, 2017: Extended Reconstructed Sea Surface Temperature, Version
5 (ERSSTv5): Upgrades, Validations, and Intercomparisons. J. Climate, 30, 8179–8205,
https://doi.org/10.1175/JCLI-D-16-0836.1.
26. Letterly, A., Key, J., and Liu, Y. (2018). Arctic climate: changes in sea ice extent outweigh
changes in snow cover, The Cryosphere, 12, 3373–3382, https://doi.org/10.5194/tc-12-3373-
2018
27. Riihelä, A., Bright, R.M. & Anttila, K. (2021). Recent strengthening of snow and ice albedo
feedback driven by Antarctic sea-ice loss. Nat. Geosci. 14, 832–836,
https://doi.org/10.1038/s41561-021-00841-x
28. Donohoe, A., & Battisti, D. S. (2011). Atmospheric and Surface Contributions to Planetary
Albedo. Journal of Climate, 24(16), 4402-4418. https://doi.org/10.1175/2011JCLI3946.1
29. Loeb, N. G., Wang, H., Rose, F. G., Kato, S., Smith, W. L., Jr, & Sun-Mack, S. (2019).
Decomposing Shortwave Top-of-Atmosphere and Surface Radiative Flux Variations in
Terms of Surface and Atmospheric Contributions. Journal of Climate, 32(16), 5003-5019.
https://doi.org/10.1175/JCLI-D-18-0826.1
13
30. Kato, S., N. G. Loeb, P. Minnis, J. A. Francis, T. P. Charlock, D. A. Rutan, E. E. Clothiaux,
and S. Sun-Mack (2006), Seasonal and interannual variations of top-of-atmosphere irradiance
and cloud cover over polar regions derived from the CERES data set, Geophys. Res. Lett.,
33, L19804, doi:10.1029/2006GL026685.
31. Zelinka et al. (2012), Computing and Partitioning Cloud Feedbacks Using Cloud Property
Histograms. Part II: Attribution to Changes in Cloud Amount, Altitude, and Optical Depth,
https://doi.org/10.1175/JCLI-D-11-00249.1
32. Klein, S. A., Hall, A., Norris, J. R., & Pincus, R. (2017). Low-cloud feedbacks from cloud-
controlling factors: A review. Shallow clouds, water vapor, circulation, and climate
sensitivity, 135-157.
33. Twomey, S. (1977). The influence of pollution on the shortwave albedo of clouds. J. atmos.
Sci, 34, 1149-1152
34. Quaas et al. (2010), Interpreting the cloud cover – aerosol optical depth relationship found in
satellite data using a general circulation model, doi:10.5194/acp-10-6129-2010
35. Li, J., Carlson, B.E., Yung, Y.L. et al. Scattering and absorbing aerosols in the climate
system. Nat Rev Earth Environ 3, 363–379 (2022). https://doi.org/10.1038/s43017-022-
00296-7
36. Taylor, K. E., Crucifix, M., Braconnot, P., Hewitt, C. D., Doutriaux, C., Broccoli, A. J., … &
Webb, M. J. (2007). Estimating shortwave radiative forcing and response in climate models.
Journal of Climate, 20(11), 2530-2543, https://doi.org/10.1175/JCLI4143.1
37. Diamond, M. S. (2023): Detection of large-scale cloud microphysical changes within a major
shipping corridor after implementation of the International Maritime Organization 2020 fuel
sulfur regulations, Atmos. Chem. Phys., 23, 8259–8269, https://doi.org/10.5194/acp-23-
8259-2023
38. Hansen, J., et al. (2005), Efficacy of climate forcings, J. Geophys. Res., 110, D18104, doi:
https://doi.org/10.1029/2005JD005776
39. Held, I. M., M. Winton, K. Takahashi, T. Delworth, F. Zeng, and G. K. Vallis, 2010: Probing
the Fast and Slow Components of Global Warming by Returning Abruptly to Preindustrial
Forcing. J. Climate, 23, 2418–2427, https://doi.org/10.1175/2009JCLI3466.1.
40. Geoffroy, O., D. Saint-Martin, D. J. L. Olivié, A. Voldoire, G. Bellon, and S. Tytéca, 2013:
Transient Climate Response in a Two-Layer Energy-Balance Model. Part I: Analytical
Solution and Parameter Calibration Using CMIP5 AOGCM Experiments. J. Climate, 26,
1841–1857, https://doi.org/10.1175/JCLI-D-12-00195.1
41. Zelinka, M. D., C. Zhou, and S. A. Klein (2016), Insights from a refined decomposition of
cloud feedbacks, Geophys. Res. Lett., 43, 9259–9269, doi:10.1002/2016GL069917
42. Zanchettin, D., Timmreck, C., Khodri, M., Schmidt, A., Toohey, M., Abe, M., Bekki, S.,
Cole, J., Fang, S.-W., Feng, W., Hegerl, G., Johnson, B., Lebas, N., LeGrande, A. N., Mann,
G. W., Marshall, L., Rieger, L., Robock, A., Rubinetti, S., Tsigaridis, K., and Weierbach, H.
(2022). Effects of forcing differences and initial conditions on inter-model agreement in the
VolMIP volc-pinatubo-full experiment, Geosci. Model Dev., 15, 2265–2292,
https://doi.org/10.5194/gmd-15-2265-2022
14
43. Li, K., Zheng, F., Zhu, J. et al. (2024). El Niño and the AMO Sparked the Astonishingly
Large Margin of Warming in the Global Mean Surface Temperature in 2023. Adv. Atmos.
Sci., https://doi.org/10.1007/s00376-023-3371-4
44. Boehm, C. L., and D. W. J. Thompson, 2023: The Key Role of Cloud–Climate Coupling in
Extratropical Sea Surface Temperature Variability. J. Climate, 36, 2753–2762,
https://doi.org/10.1175/JCLI-D-22-0362.1
45. Athanase, M., Sánchez-Benítez, A., Goessling, H.F. et al. (2024). Projected amplification of
summer marine heatwaves in a warming Northeast Pacific Ocean. Commun Earth Environ 5,
53, https://doi.org/10.1038/s43247-024-01212-1
46. Qu, X., Hall, A., Klein, S.A. et al. (2014). On the spread of changes in marine low cloud
cover in climate model simulations of the 21st century. Clim Dyn 42, 2603–2626,
https://doi.org/10.1007/s00382-013-1945-z
47. Sherwood, S. C., Webb, M. J., Annan, J. D., Armour, K. C., Forster, P. M., Hargreaves, J. C.,
et al. (2020). An assessment of Earth’s climate sensitivity using multiple lines of evidence.
Reviews of Geophysics, 58, e2019RG000678. https://doi.org/10.1029/2019RG000678
48. Smith, C. J., Kramer, R. J., Myhre, G., Alterskjær, K., Collins, W., Sima, A., Boucher, O.,
Dufresne, J.-L., Nabat, P., Michou, M., Yukimoto, S., Cole, J., Paynter, D., Shiogama, H.,
O’Connor, F. M., Robertson, E., Wiltshire, A., Andrews, T., Hannay, C., Miller, R.,
Nazarenko, L., Kirkevåg, A., Olivié, D., Fiedler, S., Lewinschal, A., Mackallah, C., Dix, M.,
Pincus, R., and Forster, P. M. (2020). Effective radiative forcing and adjustments in CMIP6
models, Atmos. Chem. Phys., 20, 9591–9618, https://doi.org/10.5194/acp-20-9591-2020
49. Kiehl, J. T. (2007), Twentieth century climate model response and climate sensitivity,
Geophys. Res. Lett., 34, L22710, doi:10.1029/2007GL031383
50. Forster, P. M., T. Andrews, P. Good, J. M. Gregory, L. S. Jackson, and M. Zelinka (2013),
Evaluating adjusted forcing and model spread for historical and future scenarios in the
CMIP5 generation of climate models, J. Geophys. Res. Atmos., 118, 1139–1150,
doi:10.1002/jgrd.50174
Acknowledgments: We thank Hans Hersbach and Adrian Simmons for answering our questions
about the interpretation of ERA5 trends and aerosol handling. Sebastian Bathiany, Tobias
Becker, Suvarchal Cheedala and Antje Boetius provided very valuable comments on a draft
version of this paper. We are grateful to the Copernicus Climate Change Service (C3S) and the
National Aeronautics and Space Administration (NASA) for the development, production and
provision of the invaluable CERES-EBAF and ERA5 data sets. We thank the German Climate
Computing Centre (DKRZ) for providing simple access to the ERA5 data and computing
resources for the data analysis.
Funding: HFG and TJ based on internal funds of the Alfred Wegener Institute, Helmholtz
Centre for Polar and Marine Research, which is part of the Helmholtz Association and
funded by the Germany Ministry of Education and Research (BMBF). This research has been
supported by the European Commission Horizon 2020 Framework Programme nextGEMS
(grant no. 101003470)
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