# Polar amplification

NASA GISS temperature trend 2000–2009, showing strong arctic amplification.

Polar amplification is the phenomenon that any change in the net radiation balance (for example greenhouse intensification) tends to produce a larger change in temperature near the poles than the planetary average.[1] On a planet with an atmosphere that can restrict emission of longwave radiation to space (a greenhouse effect), surface temperatures will be warmer than a simple planetary equilibrium temperature calculation would predict. Where the atmosphere or an extensive ocean is able to transport heat polewards, the poles will be warmer and equatorial regions cooler than their local net radiation balances would predict.[2]

In the extreme, the planet Venus is thought to have experienced a very large increase in greenhouse effect over its lifetime,[3] so much so that its poles have warmed sufficiently to render its surface temperature effectively isothermal (no difference between poles and equator).[4][5] On Earth, water vapor and trace gasses provide a lesser greenhouse effect, and the atmosphere and extensive oceans provide efficient poleward heat transport. Both palaeoclimate changes and recent global warming changes have exhibited strong polar amplification, as described below.

Arctic amplification is polar amplification of the Earth's North Pole only; Antarctic amplification is that of the South Pole.

## History

An observation based study related to Arctic amplification was published in 1969 by Mikhail Budyko,[6] the study conclusion has been summarized as, "Sea ice loss affects Arctic temperatures through the surface albedo feedback."[7][8] The same year a similar model was published by William D. Sellers.[9] Both studies attracted significant attention since they hinted at the possibility for a runaway positive feedback within the global climate system.[10] In 1975 Manabe and Wetherald published the first somewhat plausible general circulation model that looked at the effects of an increase of greenhouse gas. Although confined to less than one-third of the globe, with a "swamp" ocean and only land surface at high latitudes, it showed an Arctic warming faster than the tropics (as have all subsequent models).[11]

## Amplification

### Amplifying mechanisms

Feedbacks associated with sea ice and snow cover are widely cited as the main cause of recent terrestrial polar amplification.[12][13][14] However, amplification is also observed in model worlds with no ice or snow.[15] It appears to arise both from a (possibly transient) intensification of poleward heat transport and more directly from changes in the local net radiation balance (an overall decrease in outward radiation will produce a larger relative increase in net radiation near the poles than near the equator).[15]

Some examples of climate system feedbacks thought to contribute to recent polar amplification include the reduction of snow cover and sea ice, changes in atmospheric and ocean circulation, the presence of anthropogenic soot in the Arctic environment, and increases in cloud cover and water vapor.[13] Most studies connect sea ice changes to polar amplification.[13] Some models of modern climate exhibit Arctic amplification without changes in snow and ice cover.[16] The individual processes contributing to polar warming are critical to understanding climate sensitivity.[17]

### Ocean circulation

It has been estimated that 70% of global wind energy is transferred to the ocean and takes place within the Antarctic Circumpolar Current (ACC). Eventually, upwelling due to wind-stress transports cold Antarctic waters through the Atlantic surface current, while warming them over the equator, and into the Arctic environment. Thus, warming in the Arctic depends on the efficiency of the global ocean transport and plays a role in the polar see-saw effect.[18]

Decreased oxygen and low-pH during La Niña are processes that correlate with decreased primary production and a more pronounced poleward flow of ocean currents.[19] It has been proposed that the mechanism of increased Arctic surface air temperature anomalies during La Niña periods of ENSO may be attributed to the Tropically Excited Arctic Warming Mechanism (TEAM), when Rossby waves propagate more poleward, leading to wave dynamics and an increase in downward infrared radiation.[1][20]

### Amplification factor

Polar amplification is quantified in terms of a polar amplification factor, generally defined as the ratio of some change in a polar temperature to a corresponding change in a broader average temperature:

${\displaystyle {PAF}={\Delta {T}_{p} \over \Delta {\overline {T}}}}$  ,

where ${\displaystyle \Delta {T}_{p}}$ is a change in polar temperature and ${\displaystyle \Delta {\overline {T}}}$   is, for example, a corresponding change in a global mean temperature.

Common implementations[21][22] define the temperature changes directly as the anomalies in surface air temperature relative to a recent reference interval (typically 30 years). Others have used the ratio of the variances of surface air temperature over an extended interval.[23]

### Amplification phase

Temperature trends in West Antarctica (left) have greatly exceeded the global average; East Antarctica less so

It is observed that Arctic and Antarctic warming commonly proceed out of phase because of orbital forcing, resulting in the so-called polar see-saw effect.[24]

## Paleoclimate polar amplification

The glacial / interglacial cycles of the Pleistocene provide extensive palaeoclimate evidence of polar amplification, both from the Arctic and the Antarctic.[22] In particular, the temperature rise since the last glacial maximum 20,000 years ago provides a clear picture. Proxy temperature records from the Arctic (Greenland) and from the Antarctic indicate polar amplification factors on the order of 2.0.[22]

## Recent Arctic amplification

The dark ocean surface reflects only 6 percent of incoming solar radiation, instead sea ice reflects 50 to 70 percent.[25]

Suggested mechanisms leading to the observed Arctic amplification include Arctic sea ice decline (open water reflects less sunlight than sea ice), and atmospheric heat transport from the equator to the Arctic.[26]

Jennifer Francis told Scientific American in 2017, "A lot more water vapor is being transported northward by big swings in the jet stream. That’s important because water vapor is a greenhouse gas just like carbon dioxide and methane. It traps heat in the atmosphere. That vapor also condenses as droplets we know as clouds, which themselves trap more heat. The vapor is a big part of the amplification story—a big reason the Arctic is warming faster than anywhere else."[27]

Studies have linked rapidly warming Arctic temperatures, and thus a vanishing cryosphere, to extreme weather in mid-latitudes.[28][29][30][31] In particular, one hypothesis links polar amplification to extreme weather by changing the polar jet stream.[28] However, a 2013 study noted that extreme events in particular associated with sea ice and snow cover decline have not yet been observed for long enough to distinguish natural climate variability from impacts related to recent climate change.[32]

Studies published in 2017 and 2018 identified stalling patterns of rossby waves, in the northern hemisphere jet stream, to have caused almost stationary extreme weather events, such as the 2018 European heatwave, the 2003 European heat wave, 2010 Russian heat wave, 2010 Pakistan floods - these events have been linked to global warming, the rapid heating of the Arctic.[33][34]

According to a 2009 study the Atlantic Multi-decadal Oscillation (AMO) is highly correlated with changes in Arctic temperature, suggesting that the Atlantic Ocean thermohaline circulation is linked to temperature variability in the Arctic on a multi-decadal time scale.[35] A study in 2014 concluded that Arctic amplification significantly decreased cold-season temperature variability over the Northern Hemisphere in recent decades. Cold Arctic air intrudes into the warmer lower latitudes more rapidly today during autumn and winter, a trend projected to continue in the future except during summer, thus calling into question whether winters will bring more cold extremes.[36] According to a 2015 study, based on computer modelling of aerosols in the atmosphere, up to 0.5 degrees Celsius of the warming observed in the Arctic between 1980 and 2005 is due to aerosol reductions in Europe.[37][38]

## References

1. ^ a b Lee, Sukyoung (January 2014). "A theory for polar amplification from a general circulation perspective" (PDF). Asia-Pacific Journal of the Atmospheric Sciences. 50 (1): 31–43. Bibcode:2014APJAS..50...31L. doi:10.1007/s13143-014-0024-7.
2. ^ Pierrehumbert, R. T. (2010). Principles of Planetary Climate. Cambridge University Press. ISBN 978-0521865562.
3. ^ Kasting, J. F. (1988). "Runaway and moist greenhouse atmospheres and the evolution of Earth and Venus". Icarus. 74 (3): 472–94. Bibcode:1988Icar...74..472K. doi:10.1016/0019-1035(88)90116-9. PMID 11538226.
4. ^ Williams, David R. (15 April 2005). "Venus Fact Sheet". NASA. Retrieved 2007-10-12.
5. ^ Lorenz, Ralph D.; Lunine, Jonathan I.; Withers, Paul G.; McKay, Christopher P. (2001). "Titan, Mars and Earth: Entropy Production by Latitudinal Heat Transport" (PDF). Ames Research Center, University of Arizona Lunar and Planetary Laboratory. Retrieved 2007-08-21.
6. ^ Budyko, M.I. (1969). "The effect of solar radiation variations on the climate of the Earth". Tellus. 21 (5): 611–9. doi:10.3402/tellusa.v21i5.10109.
7. ^ Cvijanovic, Ivana; Caldeira, Ken (2015). "Atmospheric impacts of sea ice decline in CO2 induced global warming" (PDF). Climate Dynamics. 44 (5–6): 1173–86. doi:10.1007/s00382-015-2489-1.
8. ^ "Ice in Action: Sea ice at the North Pole has something to say about climate change". YaleScientific. 2016.
9. ^ Sellers, William D. (1969). "A Global Climatic Model Based on the Energy Balance of the Earth-Atmosphere System". Journal of Applied Meteorology. 8 (3): 392–400. Bibcode:1969JApMe...8..392S. doi:10.1175/1520-0450(1969)008<0392:AGCMBO>2.0.CO;2.
10. ^ Oldfield, Jonathan D. (2016). "Mikhail Budyko's (1920–2001) contributions to Global Climate Science: from heat balances to climate change and global ecology". Advanced Review. 7 (5): 682–692. doi:10.1002/wcc.412.
11. ^ Manabe, Syukoro; Wetherald, Richard T. (1975). "The Effects of Doubling the CO2 Concentration on the Climate of a General Circulation Model". Journal of the Atmospheric Sciences. 32: 3–15. doi:10.1175/1520-0469(1975)032<0003:TEODTC>2.0.CO;2.
12. ^ Hansen J., Sato M., Ruedy R. (1997). "Radiative forcing and climate response". Journal of Geophysical Research: Atmospheres. 102 (D6): 6831–64. Bibcode:1997JGR...102.6831H. doi:10.1029/96jd03436.CS1 maint: multiple names: authors list (link)
13. ^ a b c "IPCC AR5 – Near-term Climate Change: Projections and Predictability (Chapter 11 / page 983 )" (PDF). 2013. Cite journal requires |journal= (help)
14. ^ Pistone, Kristina; Eisenman, Ian; Ramanathan, Veerabhadran (2019). "Radiative Heating of an Ice-Free Arctic Ocean". Geophysical Research Letters. 46 (13): 7474–7480. doi:10.1029/2019GL082914.
15. ^ a b Alexeev V. A., Langen P. L., Bates J. R. (2005). "Polar amplification of surface warming on an aquaplanet in "ghost forcing" experiments without sea ice feedbacks". Climate Dynamics. 24 (7–8): 655–666. Bibcode:2005ClDy...24..655A. doi:10.1007/s00382-005-0018-3.CS1 maint: multiple names: authors list (link)
16. ^ Pithan, Felix; Mauritsen, Thorsten (February 2, 2014). "Arctic amplification dominated by temperature feedbacks in contemporary climate models". Nature Geoscience. 7 (3): 181–4. Bibcode:2014NatGe...7..181P. doi:10.1038/ngeo2071.
17. ^ Taylor, Patrick C., Ming Cai, Aixue Hu, Jerry Meehl, Warren Washington, Guang J. Zhang (September 23, 2013). "A Decomposition of Feedback Contributions to Polar Warming Amplification". Climate. 23 (18): 7023–43. Bibcode:2013JCli...26.7023T. doi:10.1175/JCLI-D-12-00696.1.CS1 maint: uses authors parameter (link)
18. ^ Petr Chylek, Chris K. Folland, Glen Lesins, and Manvendra K. Dubey (February 3, 2010). "Twentieth century bipolar seesaw of the Arctic and Antarctic surface air temperatures" (PDF). Geophysical Research Letters. 12 (8): 4015–22. Bibcode:2010GeoRL..37.8703C. doi:10.1029/2010GL042793.CS1 maint: uses authors parameter (link)
19. ^ Sung Hyun Nam, Hey-Jin Kim and Uwe Send (November 23, 2011). "Amplification of hypoxic and acidic events by La Niña conditions on the continental shelf off California". Geophysical Research Letters. 83 (22): L22602. Bibcode:2011GeoRL..3822602N. doi:10.1029/2011GL049549.CS1 maint: uses authors parameter (link)
20. ^ Sukyoung Lee (June 2012). "Testing of the Tropically Excited Arctic Warming Mechanism (TEAM) with Traditional El Niño and La Niña". Journal of Climate. 25 (12): 4015–22. Bibcode:2012JCli...25.4015L. doi:10.1175/JCLI-D-12-00055.1.CS1 maint: uses authors parameter (link)
21. ^ Masson-Delmotte, V., M. Kageyama, P. Braconnot, S. Charbit, G. Krinner, C. Ritz, E. Guilyardi et al. (2006). "Past and future polar amplification of climate change: climate model intercomparisons and ice-core constraints". Climate Dynamics. 26 (5): 513–529. Bibcode:2006ClDy...26..513M. doi:10.1007/s00382-005-0081-9.CS1 maint: uses authors parameter (link)
22. ^ a b c James Hansen, Makiko Sato, Gary Russell and Pushker Kharecha (September 2013). "Climate sensitivity, sea level and atmospheric carbon dioxide". Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences. 371 (2001): 20120294. arXiv:1211.4846. Bibcode:2013RSPTA.37120294H. doi:10.1098/rsta.2012.0294. PMC 3785813. PMID 24043864. Archived from the original on 2013-09-17.CS1 maint: uses authors parameter (link)
23. ^ Kobashi, T., Shindell, D. T., Kodera, K., Box, J. E., Nakaegawa, T., & Kawamura, K. (2013). "On the origin of multidecadal to centennial Greenland temperature anomalies over the past 800 yr". Climate of the Past. 9 (2): 583–596. Bibcode:2013CliPa...9..583K. doi:10.5194/cp-9-583-2013.CS1 maint: uses authors parameter (link)
24. ^ Kyoung-nam Jo, Kyung Sik Woo, Sangheon Yi, Dong Yoon Yang, Hyoun Soo Lim, Yongjin Wang, Hai Cheng & R. Lawrence Edwards (March 30, 2014). "Mid-latitude interhemispheric hydrologic seesaw over the past 550,000 years". Nature. 508 (7496): 378–382. Bibcode:2014Natur.508..378J. doi:10.1038/nature13076. PMID 24695222.CS1 maint: uses authors parameter (link)
25. ^ "Thermodynamics: Albedo". NSIDC.
26. ^ "Arctic amplification". NASA. 2013.
27. ^ Fischetti, Mark (2017). "The Arctic Is Getting Crazy". Scientific American.
28. ^ a b Francis, J. A.; Vavrus, S. J. (2012). "Evidence linking Arctic amplification to extreme weather in mid-latitudes". Geophysical Research Letters. 39 (6): L06801. Bibcode:2012GeoRL..39.6801F. doi:10.1029/2012GL051000.
29. ^ Petoukhov, Vladimir; Semenov, Vladimir A. (November 2010). "A link between reduced Barents-Kara sea ice and cold winter extremes over northern continents" (PDF). Journal of Geophysical Research: Atmospheres. 115 (21): D21111. Bibcode:2010JGRD..11521111P. doi:10.1029/2009JD013568.
30. ^ Screen, J A (November 2013). "Influence of Arctic sea ice on European summer precipitation". Environmental Research Letters. 8 (4): 044015. Bibcode:2013ERL.....8d4015S. doi:10.1088/1748-9326/8/4/044015.
31. ^ Qiuhong Tang; Xuejun Zhang; Francis, J. A. (December 2013). "Extreme summer weather in northern mid-latitudes linked to a vanishing cryosphere". Nature Climate Change. 4 (1): 45–50. Bibcode:2014NatCC...4...45T. doi:10.1038/nclimate2065.
32. ^ James E. Overland (December 8, 2013). "Atmospheric science: Long-range linkage". Nature Climate Change. 4 (1): 11–12. Bibcode:2014NatCC...4...11O. doi:10.1038/nclimate2079.
33. ^ Mann, Michael E.; Rahmstorf, Stefan (27 March 2017). "Influence of Anthropogenic Climate Change on Planetary Wave Resonance and Extreme Weather Events". Scientific Reports. 7: 45242. Bibcode:2017NatSR...745242M. doi:10.1038/srep45242. PMC 5366916. PMID 28345645.
34. ^ "Extreme global weather is 'the face of climate change' says leading scientist". The Guardian. 2018.
35. ^ Chylek, Petr; Folland, Chris K.; Lesins, Glen; Dubey, Manvendra K.; Wang, Muyin (16 July 2009). "Arctic air temperature change amplification and the Atlantic Multidecadal Oscillation". Geophysical Research Letters. 36 (14): L14801. Bibcode:2009GeoRL..3614801C. CiteSeerX 10.1.1.178.6926. doi:10.1029/2009GL038777.
36. ^ Screen, James A. (15 June 2014). "Arctic amplification decreases temperature variance in northern mid- to high-latitudes". Nature Climate Change. 4 (7): 577–582. Bibcode:2014NatCC...4..577S. doi:10.1038/nclimate2268. hdl:10871/15095.
37. ^ Harvey, C. (14 March 2016). "How cleaner air could actually make global warming worse". Washington Post.
38. ^ Acosta Navarro, J.C.; Varma, V.; Riipinen, I.; Seland, Ø.; Kirkevåg, A.; Struthers, H.; Iversen, T.; Hansson, H.-C.; Ekman, A.M.L. (2016). "Amplification of Arctic warming by past air pollution reductions in Europe". Nature Geoscience. 9 (4): 277–281. Bibcode:2016NatGe...9..277A. doi:10.1038/ngeo2673.