Observations reveal a poleward expansion of the tropics in recent decades, implying a potential role of human activity. However, although theory and modelling suggest increasing GHG concentrations should widen the tropics, previous observational-based studies depict disparate rates of expansion, including many that are far higher than those simulated by climate models. Here, we review the rates and possible causes of observed and projected tropical widening. By accounting for methodological differences, the tropics are found to have widened about 0.5° of latitude per decade since 1979. However, it is too early to detect robust anthropogenically induced widening imprints due to large internal variability. Future work should target the seasonal and regional signatures of forced widening, as well as the associated dynamical mechanisms.
Subscribe to Journal
Get full journal access for 1 year
only $17.42 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Rent or Buy article
Get time limited or full article access on ReadCube.
All prices are NET prices.
Fu, Q., Johanson, C. M., Wallace, J. M. & Reichler, T. Enhanced mid-latitude tropospheric warming in satellite measurements. Science 312, 1179 (2006).
Seidel, D. J. & Randel, W. J. Recent widening of the tropical belt: evidence from tropopause observations. J. Geophys. Res. Atmos. 112, D20113 (2007).
Seidel, D. J., Fu, Q., Randel, W. J. & Reichler, T. J. Widening of the tropical belt in a changing climate. Nat. Geosci. 1, 21–24 (2008).
Hudson, R. D., Andrade, M. F., Follette, M. B. & Frolov, A. D. The total ozone field separated into meteorological regimes – Part II: Northern Hemisphere mid-latitude total ozone trends. Atmos. Chem. Phys. 6, 5183–5191 (2006).
Hu, Y. & Fu, Q. Observed poleward expansion of the Hadley circulation since 1979. Atmos. Chem. Phys. 7, 5229–5236 (2007).
Si, D., Ding, Y. & Liu, Y. Decadal northward shift of the Meiyu belt and the possible cause. Chinese Sci. Bull. 54, 4742–4748 (2009).
Brönnimann, S. et al. Southward shift of the northern tropical belt from 1945 to 1980. Nat. Geosci. 8, 969–974 (2015).
Post, D. A. et al. Decrease in southeastern Australian water availability linked to ongoing Hadley cell expansion. Earth’s Future 2, 231–238 (2014).
Scheff, J. & Frierson, D. Twenty-first-century multimodel subtropical precipitation declines are mostly midlatitude shifts. J. Clim. 25, 4330–4347 (2012).
Feng, S. & Fu, Q. Expansion of global drylands under a warming climate. Atmos. Chem. Phys. 13, 10081–10094 (2013).
Polovina, J. J., Howell, E. A. & Abecassis, M. Ocean’s least productive waters are expanding. Geophys. Res. Lett. 35, L03618 (2008).
Irwin, A. J. & Oliver, M. J. Are ocean deserts getting larger? Geophys. Res. Lett. 36, L18609 (2009).
Moore, J. K. et al. Sustained climate warming drives declining marine biological productivity. Science 359, 1139–1143 (2018).
Studholme, J. & Gulev, S. Concurrent changes to Hadley crculation and the meridional distribution of tropical cyclones. J. Clim. 31, 4367–4389 (2018).
Rankin, W. Population Histograms (Radical Cartography, 2008); http://www.radicalcartography.net/index.html?histpop
Birner, T., Davis, S. M. & Seidel, D. J. The changing width of Earth’s tropical belt. Phys. Today 67, 38–44 (2014).
Lu, J., Vecchi, G. A. & Reichler, T. Expansion of the Hadley cell under global warming. Geophys. Res. Lett. 34, L06805 (2007).
Lu, J., Deser, C. & Reichler, T. Cause of the widening of the tropical belt since 1958. Geophys. Res. Lett. 36, L03803 (2009).
Staten, P. W., Rutz, J. J., Reichler, T. & Lu, J. Breaking down the tropospheric circulation response by forcing. Clim. Dynam. 39, 2361–2375 (2012).
Min, S.-K. & Son, S.-W. Multimodel attribution of the Southern Hemisphere Hadley cell widening: major role of ozone depletion. J. Geophys. Res. Atmos. 118, 3007–3015 (2013).
Waugh, D. W., Garfinkel, C. I. & Polvani, L. M. Drivers of the recent tropical expansion in the Southern Hemisphere: changing SSTs or ozone depletion? J. Clim. 28, 6581–6586 (2015).
Kim, Y.-H., Min, S.-K., Son, S.-W. & Choi, J. Attribution of the local Hadley cell widening in the Southern Hemisphere. Geophys. Res. Lett. 1015–1024 (2017).
Davis, N. & Birner, T. On the discrepancies in tropical belt expansion between reanalyses and climate models and among tropical belt width metrics. J. Clim. 30, 1211–1231 (2016).
Homeyer, C. R. & Bowman, K. P. Rossby wave breaking and transport between the tropics and extratropics above the subtropical jet. J. Atmos. Sci. 70, 607–626 (2012).
Waugh, D. W. et al. Revisiting the relationship among metrics of tropical expansion. J. Clim. 31, 7565–7581 (2018).
Birner, T. Recent widening of the tropical belt from global tropopause statistics: sensitivities. J. Geophys. Res. Atmos. 115, D23109 (2010).
Davis, S. M. & Rosenlof, K. H. A multidiagnostic intercomparison of tropical-width time series using reanalyses and satellite observations. J. Clim. 25, 1061–1078 (2011).
Davis, N. A., Davis, S. M. & Waugh, D. W. New insights into tropical belt metrics. Variations 16, 1–7 (2018).
Solomon, A., Polvani, L. M., Waugh, D. W. & Davis, S. M. Contrasting upper and lower atmospheric metrics of tropical expansion in the Southern Hemisphere. Geophys. Res. Lett. 43, 10496–10503 (2016).
Fu, Q. & Lin, P. Poleward shift of subtropical jets inferred from satellite-observed lower-stratospheric temperatures. J. Clim. 24, 5597–5603 (2011).
Manney, G. L. & Hegglin, M. I. Seasonal and regional variations of long-term changes in upper-tropospheric jets from reanalyses. J. Clim. 31, 423–448 (2017).
Zurita-Gotor, P. & Álvarez-Zapatero, P. Coupled interannual variability of the Hadley and Ferrel cells. J. Clim. 31, 4757–4773 (2018).
Amaya, D. J., Siler, N., Xie, S.-P., & Miller, A. J. The interplay of internal and forced modes of Hadley Cell expansion: lessons from the global warming hiatus. Clim. Dynam. 305–319 (2017)..
Allen, R. J., Sherwood, S. C., Norris, J. R. & Zender, C. S. Recent Northern Hemisphere tropical expansion primarily driven by black carbon and tropospheric ozone. Nature 485, 350–354 (2012).
Allen, R. J., Norris, J. R. & Kovilakam, M. Influence of anthropogenic aerosols and the Pacific decadal oscillation on tropical belt width. Nat. Geosci. 7, 270–274 (2014).
Hu, Y., Zhou, C. & Liu, J. Observational evidence for poleward expansion of the Hadley circulation. Adv. Atmos. Sci. 28, 33–44 (2011).
Hu, Y., Tao, L. & Liu, J. Poleward expansion of the Hadley circulation in CMIP5 simulations. Adv. Atmos. Sci. 30, 790–795 (2013).
Grise, K. M., Davis, S. M. & Staten, P. W. Regional and seasonal characteristics of the recent expansion of the tropics. J. Clim. https://doi.org/10.1175/JCLI-D-18-0060.1 (2018).
McGraw, M. C. & Barnes, E. A. Seasonal sensitivity of the eddy-driven jet to tropospheric heating in an idealized AGCM. J. Clim. 29, 5223–5240 (2016).
Johanson, C. M. & Fu, Q. Hadley cell widening: model simulations versus observations. J. Clim. 22, 2713–2725 (2009).
Tao, L., Hu, Y. & Liu, J. Anthropogenic forcing on the Hadley circulation in CMIP5 simulations. Clim. Dynam. 46, 3337–3350 (2016).
Allen, R. J. & Kovilakam, M. The role of natural climate variability in recent tropical expansion. J. Clim. 30, 6329–6350 (2017).
Mantsis, D. F., Sherwood, S., Allen, R. & Shi, L. Natural variations of tropical width and recent trends. Geophys. Res. Lett. 44, 3825–3832 (2017).
Perlwitz, J. Tug of war on the jet stream. Nat. Clim. Change 1, 29–31 (2011).
Held, I. M., Salmon, R., Fields, J. & Thiffeault, J.-L. in The General Circulation of the Atmosphere: 2000 Program in Geophysical Fluid Dynamics Technical Report No. WHOI-2001-03 1–54 (Woods Hole Oceanographic Institute, 2000); http://hdl.handle.net/1912/15
Korty, R. L. & Schneider, T. Extent of Hadley circulations in dry atmospheres. Geophys. Res. Lett. 35, L23803 (2008).
Son, S.-W., Tandon, N. F., Polvani, L. M. & Waugh, D. W. Ozone hole and Southern Hemisphere climate change. Geophys. Res. Lett. 36, L15705 (2009).
Polvani, L. M., Waugh, D. W., Correa, G. J. P. & Son, S.-W. Stratospheric ozone depletion: the main driver of twentieth-century atmospheric circulation changes in the Southern Hemisphere. J. Clim. 24, 795–812 (2010).
Son, S.-W. et al. Impact of stratospheric ozone on Southern Hemisphere circulation change: A multimodel assessment. J. Geophys. Res. Atmos. 115, D00M07 (2010).
Lucas, C., Nguyen, H. & Timbal, B. An observational analysis of Southern Hemisphere tropical expansion. J. Geophys. Res. Atmos. 117, D17112 (2012).
Robock, A., Adams, T., Moore, M., Oman, L. & Stenchikov, G. Southern Hemisphere atmospheric circulation effects of the 1991 Mount Pinatubo eruption. Geophys. Res. Lett. 34, L23710 (2007).
Barnes, E. A., Solomon, S. & Polvani, L. M. Robust wind and precipitation responses to the Mount Pinatubo eruption, as simulated in the CMIP5 models. J. Clim. 29, 4763–4778 (2016).
Kovilakam, M. & Mahajan, S. Confronting the “Indian summer monsoon response to black carbon aerosol” with the uncertainty in its radiative forcing and beyond. J. Geophys. Res. Atmos. 121, 7833–7852 (2016).
Allen, R. J. & Ajoku, O. Future aerosol reductions and widening of the northern tropical belt. J. Geophys. Res. Atmos. 121, 6765–6786 (2016).
Bonfils, C. & Santer, B. D. Investigating the possibility of a human component in various Pacific decadal oscillation indices. Clim. Dynam. 37, 1457–1468 (2011).
Newman, M. et al. The Pacific decadal oscillation, revisited. J. Clim. 29, 4399–4427 (2016).
Xu, Y. & Hu, A. How would the twenty-first-century warming influence Pacific decadal variability and its connection to North American rainfall: assessment based on a revised procedure for the IPO/PDO. J. Clim. 31, 1547–1563 (2017).
Wills, R. C., Schneider, T., Wallace, J. M., Battisti, D. S. & Hartmann, D. L. Disentangling global warming, multidecadal variability, and El Niño in Pacific temperatures. Geophys. Res. Lett. 45, 2487–2496 (2018).
Simpson, I. R. Natural variability in the width of the tropics. Variations 16, 14–20 (2018).
Lu, J., Chen, G. & Frierson, D. M. W. Response of the zonal mean atmospheric circulation to El Niño versus global warming. J. Clim. 21, 5835–5851 (2008).
Chen, G., Lu, J. & Frierson, D. M. W. Phase speed spectra and the latitude of surface westerlies: interannual variability and global warming trend. J. Clim. 21, 5942–5959 (2008).
Lau, N.-C. & Nath, M. J. A model study of heat waves over North America: meteorological aspects and projections for the twenty-first century. J. Clim. 25, 4761–4784 (2012).
Nguyen, H., Lucas, C., Evans, A., Timbal, B. & Hanson, L. Expansion of the Southern Hemisphere Hadley cell in response to greenhouse gas forcing. J. Clim. 28, 8067–8077 (2015).
Seager, R., Harnik, N., Kushnir, Y., Robinson, W. & Miller, J. Mechanisms of hemispherically symmetric climate variability. J. Clim. 16, 2960–2978 (2016).
Garfinkel, C. I., Waugh, D. W. & Polvani, L. M. Recent Hadley cell expansion: the role of internal atmospheric variability in reconciling modeled and observed trends. Geophys. Res. Lett. 42, 10824–10831 (2015).
Eyring, V. et al. Multimodel projections of stratospheric ozone in the 21st century. J. Geophys. Res. Atmos. 112, D16303 (2007).
McLandress, C. et al. Separating the dynamical effects of climate change and ozone depletion. Part II: Southern Hemisphere troposphere. J. Clim. 24, 1850–1868 (2010).
Simpson, I. R., Shaw, T. A. & Seager, R. A diagnosis of the seasonally and longitudinally varying midlatitude circulation response to global warming. J. Atmos. Sci. 71, 2489–2515 (2014).
Quan, X.-W., Hoerling, M. P., Perlwitz, J., Diaz, H. F. & Xu, T. How fast are the tropics expanding? J. Clim. 27, 1999–2013 (2013).
Barnes, E. A. Revisiting the evidence linking Arctic amplification to extreme weather in midlatitudes. Geophys. Res. Lett. 40, 4734–4739 (2013).
Grise, K. M. & Polvani, L. M. Is climate sensitivity related to dynamical sensitivity? J. Geophys. Res. Atmos. 121, 5159–5176 (2016).
Schmidt, D. F. & Grise, K. M. The response of local precipitation and sea level pressure to Hadley cell expansion. Geophys. Res. Lett. 44, 10,510–573,582 (2017).
Huang, R., Chen, S., Chen, W. & Hu, P. Interannual variability of regional Hadley circulation intensity over Western Pacific during boreal winter and its climatic impact over Asia‐Australia region. J. Geophys. Res. Atmos. 123, 344–366 (2017).
Zhang, H. & Delworth, T. L. Detectability of decadal anthropogenic hydroclimate changes over North America. J. Clim. 31, 2579–2597 (2018).
Hartmann, D.L. et al. in Climate Change 2013: The Physical Science Basis (eds Stocker, T. F. et al.) Ch. 2 (IPCC, Cambridge Univ. Press, 2013).
Choi, J., Son, S.-W., Lu, J. & Min, S.-K. Further observational evidence of Hadley cell widening in the Southern Hemisphere. Geophys. Res. Lett. 41, 2590–2597 (2014).
Lucas, C. & Nguyen, H. Regional characteristics of tropical expansion and the role of climate variability. J. Geophys. Res. Atmos. 120, 6809–6824 (2015).
Lamarque, J.-F. & Solomon, S. Impact of changes in climate and halocarbons on recent lower stratosphere ozone and temperature trends. J. Clim. 23, 2599–2611 (2010).
Archer, C. L. & Caldeira, K. Historical trends in the jet streams. Geophys. Res. Lett. 35, L08803 (2008).
Zhou, Y. P., Xu, K.-M., Sud, Y. C. & Betts, A. K. Recent trends of the tropical hydrological cycle inferred from Global Precipitation Climatology Project and International Satellite Cloud Climatology Project data. J. Geophys. Res. Atmos. 116, D09101 (2011).
Schneider, E. K. & Lindzen, R. S. Axially symmetric steady-state models of the basic state for instability and climate studies. Part I. Linearized calculations. J. Atmos. Sci. 34, 263–279 (1977).
Held, I. M. & Hou, A. Y. Nonlinear axially symmetric circulations in a nearly inviscid atmosphere. J. Atmos. Sci. 37, 515–533 (1980).
Lindzen, R. S. & Hou, A. V. Hadley circulations for zonally averaged heating centered off the Equator. J. Atmos. Sci. 45, 2416–2427 (1988).
Robinson, W. A. On the midlatitude thermal response to tropical warmth. Geophys. Res. Lett. 29, 31–34 (2002).
Walker, C. C. & Schneider, T. Eddy influences on Hadley circulations: simulations with an idealized GCM. J. Atmos. Sci. 63, 3333–3350 (2006).
Rodrigo, C. Role of eddies in the interannual variability of Hadley cell strength. Geophys. Res. Lett. 34, L22705 (2007).
Palmén, E. & Newton, C. W. Atmospheric circulation systems: their structural and physical interpretation. Science 167, 972 (1970).
Schneider, T., O’Gorman, P. A. & Levine, X. J. Water vapor and the dynamics of climate changes. Rev. Geophys. 48, RG3001 (2010).
Lu, J., Chen, G. & Frierson, D. M. W. The position of the midlatitude storm track and eddy-driven westerlies in aquaplanet AGCMs. J. Atmos. Sci. 67, 3984–4000 (2010).
Yin, J. H. A consistent poleward shift of the storm tracks in simulations of 21st century climate. Geophys. Res. Lett. 32, L18701 (2005).
Brayshaw, D. J., Hoskins, B. & Blackburn, M. The storm-track response to idealized SST perturbations in an aquaplanet GCM. J. Atmos. Sci. 65, 2842–2860 (2008).
Sampe, T., Nakamura, H., Goto, A. & Ohfuchi, W. Significance of a midlatitude SST frontal zone in the formation of a storm track and an eddy-driven westerly jet. J. Clim. 23, 1793–1814 (2009).
Rivière, G. A dynamical interpretation of the poleward shift of the jet streams in global warming scenarios. J. Atmos. Sci. 68, 1253–1272 (2011).
Tandon, N. F., Gerber, E. P., Sobel, A. H. & Polvani, L. M. Understanding Hadley cell expansion versus contraction: insights from simplified models and implications for recent observations. J. Clim. 26, 4304–4321 (2012).
Chen, G. & Held, I. M. Phase speed spectra and the recent poleward shift of Southern Hemisphere surface westerlies. Geophys. Res. Lett. 34, L21805 (2007).
Williams, G. P. Circulation sensitivity to tropopause height. J. Atmos. Sci. 63, 1954–1961 (2006).
Lorenz, D. J. Understanding midlatitude jet variability and change using Rossby wave chromatography: poleward-shifted jets in response to external forcing. J. Atmos. Sci. 71, 2370–2389 (2014).
Wittman, M. A. H., Charlton, A. J. & Polvani, L. M. the effect of lower stratospheric shear on baroclinic instability. J. Atmos. Sci. 64, 479–496 (2007).
Kidston, J. & Vallis, G. K. The relationship between the speed and the latitude of an eddy-driven jet in a stirred barotropic model. J. Atmos. Sci. 69, 3251–3263 (2012).
Lu, J., Sun, L., Wu, Y. & Chen, G. The role of subtropical irreversible PV mixing in the zonal mean circulation response to global warming-like thermal forcing. J. Clim. 27, 2297–2316 (2013).
P.W.S., K.M.G., T.B. and S.M.D. are members of working groups related to the topic of this review—the International Space Science Institute (ISSI) Tropical Width Diagnostics Intercomparison Project and the US Climate Variability and Predictability Program (US CLIVAR) Changing Width of the Tropical Belt Working Group. We thank the the ISSI and US CLIVAR offices, and sponsoring agencies (the ESA, Swiss Confederation, Swiss Academy of Sciences, University of Bern, NASA, NOAA, NSF and DOE) for supporting these groups and activities. J.L. is supported by the US Department of Energy Office of Science Biological and Environmental Research (BER) as part of the Regional and Global Climate Modeling Program. We acknowledge F. Liu for his assistance in drawing Fig. 4.
The authors declare no competing interests.
Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
About this article
Cite this article
Staten, P.W., Lu, J., Grise, K.M. et al. Re-examining tropical expansion. Nature Clim Change 8, 768–775 (2018). https://doi.org/10.1038/s41558-018-0246-2
Observed low-frequency linkage between Northern Hemisphere tropical expansion and polar vortex weakening from 1979 to 2012
Atmospheric Research (2020)
Singapore Journal of Tropical Geography (2020)
Seasonal and Annual Changes of the Regional Tropical Belt in GPS-RO Measurements and Reanalysis Datasets
Journal of Climate (2020)
Geophysical Research Letters (2020)
Climate Dynamics (2020)