Hydrologic impacts of past shifts of Earth’s thermal equator offer insight into those to be produced by fossil fuel CO
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Broecker, Wallace S.; Putnam, Aaron E.

doi:10.1073/pnas.1301855110

Cited by 81 publications

(55 citation statements)

References 66 publications

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“…Although there is no consensus among climate models, most simulations for the coming decades also suggest changes in precipitation in the subtropical regions-in particular an increase over the Sahel in northern Africa (11)(12)(13)-that can lead to a reduction of dust emission (10). Large changes in dust emissions (14,15) and precipitation over the Sahel (16)(17)(18) have already occurred during the Holocene (i.e., the last 12,000 y) as shown by previous studies, and modifications in those parameters during warm climate periods of the past may offer useful insights into future climatic change (19). In particular, it may be feasible to better constrain future changes in TC activity by improving understanding of the relationships between the joint behavior of Sahel/Sahara vegetation cover, dust emissions from these regions, and tropical storminess during the Holocene Thermal Maximum (11,000-5,000 yBP).…”

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confidence: 83%

Tropical cyclone activity enhanced by Sahara greening and reduced dust emissions during the African Humid Period

Pausata

Emanuel

Chiacchio

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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Tropical cyclones (TCs) can have devastating socioeconomic impacts. Understanding the nature and causes of their variability is of paramount importance for society. However, historical records of TCs are too short to fully characterize such changes and paleosediment archives of Holocene TC activity are temporally and geographically sparse. Thus, it is of interest to apply physical modeling to understanding TC variability under different climate conditions. Here we investigate global TC activity during a warm climate state (mid-Holocene, 6,000 yBP) characterized by increased boreal summer insolation, a vegetated Sahara, and reduced dust emissions. We analyze a set of sensitivity experiments in which not only solar insolation changes are varied but also vegetation and dust concentrations. Our results show that the greening of the Sahara and reduced dust loadings lead to more favorable conditions for tropical cyclone development compared with the orbital forcing alone. In particular, the strengthening of the West African Monsoon induced by the Sahara greening triggers a change in atmospheric circulation that affects the entire tropics. Furthermore, whereas previous studies suggest lower TC activity despite stronger summer insolation and warmer sea surface temperature in the Northern Hemisphere, accounting for the Sahara greening and reduced dust concentrations leads instead to an increase of TC activity in both hemispheres, particularly over the Caribbean basin and East Coast of North America. Our study highlights the importance of regional changes in land cover and dust concentrations in affecting the potential intensity and genesis of past TCs and suggests that both factors may have appreciable influence on TC activity in a future warmer climate.hurricanes | mid-Holocene | dust emissions | vegetation changes | land cover changes

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confidence: 83%

Tropical cyclone activity enhanced by Sahara greening and reduced dust emissions during the African Humid Period

Pausata

Emanuel

Chiacchio

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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“…Changes in ITA related to external forcings are of particular interest given their potential effect in displacing the intertropical convergence zone, with the implication that the current precipitation patterns over large parts of the world could change (Broecker and Putnam, 2013;Seo et al, 2016). However, our analysis shows that, although there is a trend in ITA that can be traced to changes in anthropogenic forcings, the structural break in the level and the slope registered in the late 1960s is very likely the product of combining low-frequency variability of different magnitudes, phases and periods that are contained in the temperatures of the northern and southern hemispheres.…”

Section: Discussionmentioning

confidence: 99%

“…The temperature contrast between hemispheres has emerged in the literature as an indicator of climate change (Friedman et al, 2013). Changes in ITA linked to increases in radiative forcing are of particular interest given its potential effect in displacing the intertropical convergence zone and with it the current precipitation patterns over large parts of the world could change (Broecker and Putnam, 2013;Seo et al, 2016). The observed ITA has been characterized as showing no trend during most of the 20th century but having an increasing trend of about 0.17 ºC per decade since 1980.…”

Section: Testing For a Common Secular Trend Between Temperatures And mentioning

confidence: 99%

Characterizing and attributing the warming trend in sea and land surface temperatures

Estrada

Martins

Perron³

2017

Atm

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RESUMENDebido a la variabilidad interna de baja frecuencia, las tendencias del calentamiento observadas y subyacentes en series de temperatura pueden ser marcadamente diferentes. Las temperaturas hemisféricas están caracterizadas por importantes discrepancias en las tendencias no lineales observadas, sugiriendo que los hemisferios norte y sur han respondido de manera diferente a los cambios en el forzamiento radiativo. Mediante la utilización de técnicas econométricas recientes es posible reconciliar estas diferencias y mostrar que todas las temperaturas terrestres y oceánicas comparten propiedades de series de tiempo similares, así como una tendencia subyacente común de origen antrópico. También se investiga la asimetría inter-hemisférica de temperatura (ITA, por sus siglas en inglés) y se muestra que la diferencia en el calentamiento entre hemisferios se debe en parte al forzamiento antrópico, pero que la mayoría de los cambios rápidos observados son probablemente producto de la variabilidad natural. La atribución de cambios en la ITA es importante porque los aumentos en el contraste de temperaturas entre hemisferios podrían ocasionar un desplazamiento de la zona intertropical de convergencia y alterar los patrones de precipitación. También se investigan la existencia y causas de una reciente ralentización en el calentamiento. Los resultados sugieren que dicha lentificación es una característica común de las temperaturas hemisféricas globales tanto en tierra como en el océano, y que puede atribuirse al menos parcialmente a cambios en el forzamiento antrópico. ABSTRACTBecause of low-frequency internal variability, the observed and underlying warming trends in temperature series can be markedly different. Important differences in the observed nonlinear trends in hemispheric temperature series suggest that the northern and southern hemispheres have responded differently to the changes in the radiative forcing. Using recent econometric techniques, we can reconcile such differences and show that all sea and land temperatures share similar time series properties and a common underlying warming trend having a dominant anthropogenic origin. We also investigate the interhemispheric temperature asymmetry (ITA) and show that the differences in warming between hemispheres are in part driven by anthropogenic forcing but that most of the observed rapid changes is likely due to natural variability. The attribution of changes in ITA is relevant since increases in the temperature contrast between hemispheres could potentially produce a shift in the Intertropical Convergence Zone and alter rainfall patterns. The existence of a current slowdown in the warming and its causes are also investigated. The results suggest that the slowdown is a common feature in global and hemispheric sea and land temperatures that can, at least partly, be attributed to changes in anthropogenic forcing.

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“…At equilibrium (stable lake level), the amount of water evaporating from the lake surface matches the inflow into the lake, which is calculated as the fraction of precipitation in the catchment that enters the lake as runoff multiplied by the catchment area of the lake and precipitation amount (20). To constrain the model, we first investigated the modern lake using satellite imagery, lake and stream chemistry, and longterm measurements of precipitation, air temperature, and evaporation (SI Materials and Methods).…”

Section: ) and Southmentioning

confidence: 99%

Northward extent of East Asian monsoon covaries with intensity on orbital and millennial timescales

Goldsmith

Broecker

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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The magnitude, rate, and extent of past and future East Asian monsoon (EAM) rainfall fluctuations remain unresolved. Here, late Pleistocene-Holocene EAM rainfall intensity is reconstructed using a well-dated northeastern China closed-basin lake area record located at the modern northwestern fringe of the EAM. The EAM intensity and northern extent alternated rapidly between wet and dry periods on time scales of centuries. Lake levels were 60 m higher than present during the early and middle Holocene, requiring a twofold increase in annual rainfall, which, based on modern rainfall distribution, requires a ∼400 km northward expansion/migration of the EAM. The lake record is highly correlated with both northern and southern Chinese cave deposit isotope records, supporting rainfall "intensity based" interpretations of these deposits as opposed to an alternative "water vapor sourcing" interpretation. These results indicate that EAM intensity and the northward extent covary on orbital and millennial timescales. The termination of wet conditions at 5.5 ka BP (∼35 m lake drop) triggered a large cultural collapse of Early Neolithic cultures in north China, and possibly promoted the emergence of complex societies of the Late Neolithic.East Asian monsoon | closed-basin lake | paleo-rainfall | Chinese cave record | northward expansion T he East Asian monsoon (EAM) is a major component of the global climate system (1), and its variability directly impacts the lives of over a billion people. Understanding EAM sensitivity to past climate changes and its future variability are essential for determining the EAM response to different climate forcings and for constraining future climate projections. Two competing interpretations of existing paleoclimate records frame our current understanding of the response of the EAM to orbital-scale and high-latitude millennial-scale forcing during the late PleistoceneHolocene. The first interpretation suggests that oxygen isotopic records from Chinese cave deposits reflect real rainfall changes, indicating a direct response of EAM rains to external climate forcings (2-4). The competing view holds that these isotopic records reflect changes in moisture sourcing and depend on the Indian Monsoon intensity (5-10), suggesting that the cave deposit isotopic values are decoupled from actual rainfall amounts, and thus question the validity of oxygen isotope-based EAM intensity reconstructions. Missing from this debate has been an independent quantitative record of past rainfall variability in the EAM region.Here, we present a detailed, well-dated lake-level history for Lake Dali (43.15°N, 116.29°E), a closed-basin lake in Inner Mongolia (1,220 m above sea level, 220 km 2 lake area and maximum depth of 11 m), presently located near the northwestern limit of EAM domain (e.g., ref. 11; Fig. 1). The peripheral location of Lake Dali with respect to the monsoon region provides an excellent opportunity to examine the magnitude of spatial expansion of the EAM and whether the millennial-and orbital-scale change...

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Hydrologic impacts of past shifts of Earth’s thermal equator offer insight into those to be produced by fossil fuel CO ₂

Cited by 81 publications

References 66 publications

Tropical cyclone activity enhanced by Sahara greening and reduced dust emissions during the African Humid Period

Tropical cyclone activity enhanced by Sahara greening and reduced dust emissions during the African Humid Period

Characterizing and attributing the warming trend in sea and land surface temperatures

Northward extent of East Asian monsoon covaries with intensity on orbital and millennial timescales

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Hydrologic impacts of past shifts of Earth’s thermal equator offer insight into those to be produced by fossil fuel CO 2

Cited by 81 publications

References 66 publications

Tropical cyclone activity enhanced by Sahara greening and reduced dust emissions during the African Humid Period

Tropical cyclone activity enhanced by Sahara greening and reduced dust emissions during the African Humid Period

Characterizing and attributing the warming trend in sea and land surface temperatures

Northward extent of East Asian monsoon covaries with intensity on orbital and millennial timescales

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Hydrologic impacts of past shifts of Earth’s thermal equator offer insight into those to be produced by fossil fuel CO ₂