Mid-Holocene climates of the Americas: a dynamical response to changed seasonality

Harrison, Sandy P.; Kutzbach, John E.; Liu, Z.; Bartlein, Patrick J.; Otto‐Bliesner, Bette L.; Muhs, Daniel R.; Prentice, I. Colin; Thompson, Robert S.

doi:10.1007/s00382-002-0300-6

Cited by 180 publications

(147 citation statements)

References 70 publications

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“…6). The 6 ka changes over Africa, India, and North America are consistent with proxy records of lake levels (Kohfeld and Harrison, 2000;Yu et al, 2000;Harrison et al, 2003). In particular, over Africa, not only moistening over the Sahara but also moistening over the tropical coastal area of Eastern Africa is reproduced by the models.…”

Section: Atmospheric Changes At 6 Kasupporting

confidence: 79%

“…The period 6 ka is characterized by enhanced seasonality in the Northern Hemisphere and reduced seasonality in the Southern Hemisphere due to a difference in solar insolation compared with the present-day, associated with orbital variations of the Earth (Berger, 1978). Many proxy records such as pollen Harrison et al, 2001;Bigelow et al, 2003;Pickett et al, 2004;Wohlfahrt et al, 2008;Bartlein et al, 2011) and lake level (Kohfeld and Harrison, 2000;Yu et al, 2000;Harrison et al, 2003;Lezine et al, 2011) suggest humid and vegetated conditions over the Sahara, and a northward shift of vegetation in the northern high latitudes.…”

Section: Introductionmentioning

confidence: 99%

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Can an Earth System Model simulate better climate change at mid-Holocene than an AOGCM? A comparison study of MIROC-ESM and MIROC3

et al. 2013

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The importance of evaluating models through paleoclimate simulations is becoming more recognized in efforts to improve climate projection. To evaluate an integrated Earth System Model, MIROC-ESM, we performed simulations in time-slice experiments for the mid-Holocene (6000 yr before present, 6 ka) and preindustrial (1850 AD, 0 ka) periods under the protocol of the Coupled Model Intercomparison Project 5/Paleoclimate Modelling Intercomparison Project 3. We first give an overview of the simulated global climates by comparing with simulations using a previous version of the MIROC model (MIROC3), which is an atmosphere–ocean coupled general circulation model. We then comprehensively discuss various aspects of climate change with 6 ka forcing and how the differences in the models can affect the results. We also discuss the representation of the precipitation enhancement at 6 ka over northern Africa. The precipitation enhancement at 6 ka over northern Africa according to MIROC-ESM does not differ greatly from that obtained with MIROC3, which means that newly developed components such as dynamic vegetation and improvements in the atmospheric processes do not have significant impacts on the representation of the 6 ka monsoon change suggested by proxy records. Although there is no drastic difference between the African monsoon representations of the two models, there are small but significant differences in the precipitation enhancement over the Sahara in early summer, which can be related to the representation of the sea surface temperature rather than the vegetation coupling in MIROC-ESM. Because the oceanic parts of the two models are identical, the difference in the sea surface temperature change is ultimately attributed to the difference in the atmospheric and/or land modules, and possibly the difference in the representation of low-level clouds

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Section: Atmospheric Changes At 6 Kasupporting

confidence: 79%

Section: Introductionmentioning

confidence: 99%

Can an Earth System Model simulate better climate change at mid-Holocene than an AOGCM? A comparison study of MIROC-ESM and MIROC3

et al. 2013

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“…FOAM was designed for long century-scale integrations and exhibits minimal ocean drift with no flux corrections (Wu et al, 2003). FOAM's simulation of modern climate shows reasonable agreement with present-day observations and NCAR CSM (Harrison et al, 2003). FOAM has been widely used to study climate change through geological time (e.g.…”

Section: Experimental Designmentioning

confidence: 88%

Amplification of obliquity forcing through mean annual and seasonal atmospheric feedbacks

Lee

Poulsen

2008

Clim. Past

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Abstract. Pleistocene benthic δ 18 O records exhibit strong spectral power at ∼41 kyr, indicating that global ice volume has been modulated by Earth's axial tilt. This feature, and weak spectral power in the precessional band, has been attributed to the influence of obliquity on mean annual and seasonal insolation gradients at high latitudes. In this study, we use a coupled ocean-atmosphere general circulation model to quantify changes in continental snowfall associated with mean annual and seasonal insolation forcing due to a change in obliquity. Our model results indicate that insolation changes associated with a decrease in obliquity amplify continental snowfall in three ways: (1) Local reductions in air temperature enhance precipitation as snowfall. (2) An intensification of the winter meridional insolation gradient strengthens zonal circulation (e.g. the Aleutian low), promoting greater vapor transport from ocean to land and snow precipitation. (3) An increase in the summer meridional insolation gradient enhances summer eddy activity, increasing vapor transport to high-latitude regions. In our experiments, a decrease in obliquity leads to an annual snowfall increase of 25.0 cm; just over one-half of this response (14.1 cm) is attributed to seasonal changes in insolation. Our results indicate that the role of insolation gradients is important in amplifying the relatively weak insolation forcing due to a change in obliquity. Nonetheless, the total snowfall response to obliquity is similar to that due to a shift in Earth's precession, suggesting that obliquity forcing alone can not account for the spectral characteristics of the ice-volume record.

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“…Not all portions of North America experienced this trend, however, and the Pacific Northwest and the southern tropics, in particular, were characterized by drying toward present. In many areas, the changes continue trends that persisted for millennia during the Holocene, and the patterns may indicate the continuation of long-term, low-20 frequency responses of Hadley circulation, the position and influence of the subtropical high systems, and the major westerly storm tracks to orbital and greenhouse gas forcing (Braconnot et al, 2007;Harrison et al, 2003).…”

Section: Discussionmentioning

confidence: 99%

“…Changes in global forcing, such as slow changes in seasonal insolation and greenhouse gases, can explain many of the Holocene-scale trends (Shuman and Marsicek, 5 2016). Climate models run with mid-Holocene (4050 BCE or 6000 YBP) forcings simulate extensive drying, which must have been followed by moistening towards the present, because of dynamical responses of the atmosphere to seasonal insolation change, sea-surface conditions in the tropical Pacific and Atlantic, and surface-atmosphere feedbacks (Diffenbaugh et al, 2006;Harrison et al, 2003;Shin et al, 2006). Because of the responses to external forcing, the Common Era and especially the second millennium CE stand out as the wettest periods of the Holocene over much of North America, 10 despite the decadal "mega-droughts" that occasionally punctuated the persistence of the relatively wet conditions.…”

Section: Differences Between the First And Second Millennia 25mentioning

confidence: 99%

Millennial-to-centennial patterns and trends in the hydroclimate of North America over the past 2000 years

Shuman

Routson

McKay

et al. 2017

Preprint

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Abstract.A synthesis of 93 hydrologic records from across North and Central America, and adjacent tropical and Arctic islands, reveals centennial to millennial trends in the regional hydroclimates of the Common Era (CE; past 2000 years). The hydrological records derive from materials stored in lakes, bogs, caves, and ice from extant glaciers, which have the continuity through time to preserve low-frequency (>100 year) climate signals that may not be well represented by other 20 shorter-lived archives, such as tree-ring chronologies. The most common pattern, represented in 46 (49%) of the records, indicates that the centuries before 1000 CE were drier than the centuries since that time. Principal components analysis indicates that millennial-scale trends represent the dominant pattern of variance in the southwest and northeast U.S., the midcontinent, Pacific Northwest, the Arctic, and the tropics, although not all records within a region show the same direction of change. The Pacific Northwest, Greenland, and the southernmost tier of the tropical sites tended to dry toward present, as 25 many other areas became wetter than before. Twenty-two records (24%) indicate that the Medieval period (800-1300 CE) was drier than the Little Ice Age (1400-1900 CE), but in many cases the difference was part of the longer millennial-scale trend, and, in 25 records (27%), the Medieval period represented a pluvial (wet) phase. Where quantitative records permitted a comparison, we found that centennial-scale fluctuations over the Common Era represented changes of 3-7% of the modern inter-annual range of variability in precipitation, but the accumulation of these long-term trends over the entirety of the 30Holocene caused recent centuries to be significantly wetter, on average, than most of the past 11,000 years.

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Mid-Holocene climates of the Americas: a dynamical response to changed seasonality

Cited by 180 publications

References 70 publications

Can an Earth System Model simulate better climate change at mid-Holocene than an AOGCM? A comparison study of MIROC-ESM and MIROC3

Can an Earth System Model simulate better climate change at mid-Holocene than an AOGCM? A comparison study of MIROC-ESM and MIROC3

Amplification of obliquity forcing through mean annual and seasonal atmospheric feedbacks

Millennial-to-centennial patterns and trends in the hydroclimate of North America over the past 2000 years

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