On the Origin of the Surface Air Temperature Difference between the Hemispheres in Earth's Present-Day Climate

Abstract

In today's climate, the annually averaged surface air temperature in the Northern Hemisphere (NH) is 18-28C higher than in the Southern Hemisphere (SH). Historically, this interhemispheric temperature difference has been attributed to a number of factors, including seasonal differences in insolation, the larger area of (tropical) land in the NH, the particularities of the Antarctic in terms of albedo and temperature, and northward heat transport by ocean circulation. A detailed investigation of these factors and their contribution to the temperature difference, however, has to the authors' knowledge not been performed so far. Here the origin of the interhemispheric temperature difference is traced using an assessment of climatological data and the observed energy budget of Earth as well as model simulations. It is found that for the preindustrial climate the temperature difference is predominantly due to meridional heat transport in the oceans, with an additional contribution from the albedo differences between the polar regions. The combination of these factors (that are to some extent coupled) governs the evolution of the temperature difference over the past millennium. Since the beginning of industrialization the interhemispheric temperature difference has increased due to melting of sea ice and snow in the NH. Furthermore, the predicted higher rate of warming over land as compared to the oceans contributes to this increase. Simulations for the twenty-first century show that the interhemispheric temperature difference continues to grow for the highest greenhouse gas emission scenarios due to the land-ocean warming contrast and the strong loss of Arctic sea ice, whereas the decrease in overturning strength dominates for the more moderate scenarios.

Projected effects of declining aerosols in RCP4.5: unmasking global warming?

“…The NH is expected to warm more rapidly than the SH under strong long-lived GHG forcing due to its larger proportion of land, and deep ocean mixing in the SH. However, a weakening of northward heat transport by the Atlantic meridional overturning circulation (AMOC) can exert the dominant control on the inter-hemispheric warming difference under moderate warming scenarios (Feulner et al, 2013). Our simulations do exhibit a strong "warming hole" over the mid-latitude North Atlantic (not shown), indicative of a substantial weakening of the AMOC (Drijfhout et al, 2012).…”

Influência da inclinação do eixo de rotação da Terra na temperatura do ar global

“…5 a-b-c-e) é que o aquecimento na região tropical não ocorre de maneira simétrica em ambos os hemisférios; no HN a área mais quente é ligeiramente mais extensa latitudinalmente e, segundo Feulner et al (2013), isso torna o HN entre 1º a 2º C mais quente do que o HS na média anual. Feulner et al (2013) e Kang et al (2015) mencionam que historicamente as diferenças de temperatura entre os hemisférios norte e sul têm sido atribuídas há vários fatores, como: ao HN ter mais área continental e, portanto, se aquecer mais no verão devido à menor capacidade térmica em relação ao oceano e pelo transporte de calor dos oceanos austrais para o HN. Ambos, Feulner et al (2013) e Kang et al (2015) fizeram estudos com modelos numéricos e mostraram a importância do transporte meridional de calor nos oceanos do HS para o HN como principal causa das diferenças de temperatura inter-hemisféricas.…”

“…Feulner et al (2013) e Kang et al (2015) mencionam que historicamente as diferenças de temperatura entre os hemisférios norte e sul têm sido atribuídas há vários fatores, como: ao HN ter mais área continental e, portanto, se aquecer mais no verão devido à menor capacidade térmica em relação ao oceano e pelo transporte de calor dos oceanos austrais para o HN. Ambos, Feulner et al (2013) e Kang et al (2015) fizeram estudos com modelos numéricos e mostraram a importância do transporte meridional de calor nos oceanos do HS para o HN como principal causa das diferenças de temperatura inter-hemisféricas. Entretanto, Feulner et al (2013) também mencionam uma contribuição adicional da diferença de albedo entre as regiões polares.…”

“…Ambos, Feulner et al (2013) e Kang et al (2015) fizeram estudos com modelos numéricos e mostraram a importância do transporte meridional de calor nos oceanos do HS para o HN como principal causa das diferenças de temperatura inter-hemisféricas. Entretanto, Feulner et al (2013) também mencionam uma contribuição adicional da diferença de albedo entre as regiões polares. Já para Kang et al (2015), a contribuição adicional seria a diferença no aprisionamento dos gases de efeito estufa em ambos os hemisférios.…”

The role of the North Atlantic overturning and deep ocean for multi-decadal global-mean-temperature variability

“…Atlantic variability is found to contribute significantly to Northern Hemisphere variations Knight et al, 2005Knight et al, , 2006 and eventually to global mean temperature (GMT). Zanchettin et al (2010) find multi-decadal AMOC variations to be a major source of GMT variability over the last millennium, and Feulner et al (2013) report meridional heat transport in the Atlantic to be the dominant process behind the persistent temperature difference between the Northern Hemisphere and Southern Hemisphere in an unperturbed climate. Results of a multi-model intercomparison suggest that multi-decadal variability in the high northern latitudes might be a major source of deviations within the CMIP5 model ensemble and in comparison with observational data over the 20th century (Jones et al, 2013).…”