Comment on "Radiative forcings for 28 potential Archean greenhouse gases" by Byrne and Goldblatt (2014)
Summary: In the article Clim Past 10, 1779 (2014), the HITRAN2012 database was employed to evaluate the radiative forcing of 28 Archean gases. The authors claimed that for NO2, H2O2, C2H4, CH3OH, and CH3Br there are severe disagreements between cross sections generated from the HITRAN line-by-line data and those of the PNNL experimental database. In this work we show that the differences are not nearly at the scale suggested by the authors, and their conclusions about these gases and HO2 are not correct.
Clim. Past Discuss., 11, 1985-2007, doi:10.5194/cpd-11-1985-2015, 2015
Carbon cycle dynamics during recent interglacials
Clim. Past Discuss., 11, 1945-1983, doi:10.5194/cpd-11-1945-2015, 2015
Miocene–Pliocene stepwise intensification of the Benguela upwelling over the Walvis Ridge off Namibia
Clim. Past Discuss., 11, 1913-1943, doi:10.5194/cpd-11-1913-2015, 2015
Climatic variability and human impact during the last 2000 years in western Mesoamerica: evidences of late Classic and Little Ice Age drought events
Summary: We present results from western Mexico, where very few paleoclimatic research sites exist. The record has good chronological resolution (ca. 20yr) and clear climatic trends during the last 2ka. The most important signals are: 1. dry conditions during the late Classic (AD 500 to 1000), specially from AD 600 to 800 and 2. low lake levels during the LIA, in two phases that follow Spörer and Maunder solar minima. Dryer conditions are realted wtih a lower intentisty of the North American Monsoon.
Clim. Past Discuss., 11, 1887-1911, doi:10.5194/cpd-11-1887-2015, 2015
Carbon isotope excursions in paleosol carbonate marking five early Eocene hyperthermals in the Bighorn Basin, Wyoming
Summary: Ancient greenhouse warming episodes are studied in river floodplain sediments in the western interior of the USA. Paleohydrological changes reveal to be opposite for four smaller warming episodes than for the largest, most-studied event. Carbon cycle tracers are used to unravel whether this largest event was a similar event but scaled to the smaller ones, or if this event was distinct not only in size but also in carbon sourcing, for which the current work cannot come with a definitive solution.
Clim. Past Discuss., 11, 1857-1885, doi:10.5194/cpd-11-1857-2015, 2015
Multi-century lake area changes in the Andean high-elevation ecosystems of the Southern Altiplano
Clim. Past Discuss., 11, 1821-1855, doi:10.5194/cpd-11-1821-2015, 2015
Frequency, magnitude and character of hyperthermal events at the onset of the Early Eocene Climatic Optimum
Summary: Several episodes of global warming took place during greenhouse conditions in the early Eocene and are recorded in deep-sea sediments. The stable carbon and oxygen isotope records are used to investigate the magnitude of six of these events describing their effects on the global carbon cycle and the associated temperature response. Findings indicate that these events share a common nature and hint to the presence of multiple sources of carbon release.
Clim. Past Discuss., 11, 1795-1820, doi:10.5194/cpd-11-1795-2015, 2015
A collection of sub-daily pressure and temperature observations for the early instrumental period with a focus on the "year without a summer" 1816
Summary: A dataset of instrumental pressure and temperature observations for the early instrumental period (before ca. 1850) is described. This is the result of a digitisation effort involving the period immediately after the eruption of Mount Tambora in 1815, combined with the collection of already available sub-daily time series. The highest data availability is therefore for the years 1815 to 1817. An analysis of pressure variability and of case studies in Europe is performed for that period.
Clim. Past Discuss., 11, 1741-1794, doi:10.5194/cpd-11-1741-2015, 2015
Rapid millennial-scale vegetation changes in the tropical Andes
Summary: We compare eight pollen records reflecting environmental change in the tropical Andes over the past 50,000 years. We identify rapid responses of the tropical vegetation to millennial-scale climate variability, and relate differences between sites to moisture sources and site sensitivity.
Clim. Past Discuss., 11, 1701-1739, doi:10.5194/cpd-11-1701-2015, 2015
Astronomical calibration of the geological timescale: closing the middle Eocene gap
Summary: Testing hypotheses for mechanisms and dynamics of past climate change rely on the accuracy of geological dating. Development of a highly accurate geological time scale for the Cenozoic Era has previously been hampered by discrepancies between radio-isotopic and astronomical dating methods, and a stratigraphic gap in the middle Eocene. We close this gap and provide a fundamental advance in establishing a reliable and highly accurate geological time scale for the last 66 million years.
Clim. Past Discuss., 11, 1665-1699, doi:10.5194/cpd-11-1665-2015, 2015
The Eocene–Oligocene transition at ODP Site 1263, Atlantic Ocean: decreases in nannoplankton size and abundance and correlation with benthic foraminiferal assemblages
Summary: Deep-sea sediments at ODP Site 1263 (Walvis Ridge, South Atlantic) show that marine calcifying algae decreased in abundance and size at the Eocene-Oligocene boundary, when the Earth transitioned from a greenhouse to a more glaciated and cooler climate. This decreased the food supply for benthic foraminifer communities. The plankton rapidly responded to fast-changing conditions, such as seasonal nutrient availability, or to threshold-levels in pCO2, cooling and ocean circulation.
Clim. Past Discuss., 11, 1615-1664, doi:10.5194/cpd-11-1615-2015, 2015
Stability of ENSO and its tropical Pacific teleconnections over the Last Millennium
Clim. Past Discuss., 11, 1579-1613, doi:10.5194/cpd-11-1579-2015, 2015
Stability of the vegetation–atmosphere system in the early Eocene climate
Clim. Past Discuss., 11, 1551-1578, doi:10.5194/cpd-11-1551-2015, 2015
The historic reality of the cyclonic variability in French Antilles, 1635–2007
Summary: Facing climate change and increasing costs of natural disasters, the exposure analysis requires having a long-term knowledge of the impacts of extreme events. The research based on historical archives made it possible to reconstruct, for the first time, the chronology and severity of hurricanes in the French Antilles since the 17th century. The analysis of a historical period highlights the variability of cyclonic activity and the interest of pluridisciplinary scientific perspectives.
Clim. Past Discuss., 11, 1519-1550, doi:10.5194/cpd-11-1519-2015, 2015
Variability of daily winter wind speed distribution over Northern Europe during the past millennium in regional and global climate simulations
Clim. Past Discuss., 11, 1479-1518, doi:10.5194/cpd-11-1479-2015, 2015
Phase relationships between orbital forcing and the composition of air trapped in Antarctic ice cores
Summary: We present new measurements of dO2/N2 and d18Oatm performed on well-conserved ice from EDC between MIS5 and 380-800 ka. We present a multi-proxy comparison over MIS 5 of EDC, Vostok and Dome F. Our results indicate that the dO2/N2 can be influenced by local climatic parameters. Then, combining Vostok and EDC records, we are able to discuss the delay between d18Oatm and precession over the last 800 ka. This delay has varied through time, periods of larger delay are associated with Heinrich events
Clim. Past Discuss., 11, 1437-1477, doi:10.5194/cpd-11-1437-2015, 2015
Millennial-scale precipitation variability over Easter Island (South Pacific) during MIS 3: inter-hemispheric teleconnections with North Atlantic abrupt cold events
Summary: The Rano Aroi peat record (Easter Island, 27ºS) is characterized by six major events of enhanced precipitation between 38 and 65 kyr BP coinciding with Heinrich and Dansgaard-Oeschger (DO) Stadials. These events draw a coherent regional picture involving atmospheric and oceanic reorganization. The singular location of Easter Island, filling a gap in an area where marine records are not available, contributes to understand the mechanisms behind these global rapid climatic excursions.
Clim. Past Discuss., 11, 1407-1435, doi:10.5194/cpd-11-1407-2015, 2015
Mammal faunal response to the Paleogene hyperthermals ETM2 and H2
Summary: This project describes mammal faunal response to the ETM2 and H2 hyperthermals (rapid global warming events) of the early Paleogene, including changes in faunal structure and species relative body size. Comparative analysis demonstrates that response is proportionate to the magnitude of climate change, and environmental moisture and rate of change are important moderators of response. Results permit prediction of faunal response to anthropogenically-driven warming across North America.
Clim. Past Discuss., 11, 1371-1405, doi:10.5194/cpd-11-1371-2015, 2015
Variability in terrigenous sediment supply offshore of the Rio de la Plata (Uruguay) recording the continental climatic history over the past 1200 years
Summary: The observed changes in the proxy records indicate variations in the continental runoff and the marine influence, related to regional climatic variability (the Medieval Climatic Anomaly and the Little Ice Age). Therefore, we put forward the suggestion that global atmospheric changes (mainly the latitudinal shifts of the ITCZ and the ENSO events) have made an impact on the local sedimentation regime, on the inner Uruguayan continental shelf over the past 1200 cal yr BP (750-2000 AD).
Clim. Past Discuss., 11, 1343-1369, doi:10.5194/cpd-11-1343-2015, 2015
Early warnings and missed alarms for abrupt monsoon transitions
Summary: Using a combination of speleothem records and model simulations of the East Asian Monsoon over the penultimate glacial cycle, we search for early warning signals of past tipping points. We detect a characteristic slower response to perturbations prior to an abrupt monsoon shift at the glacial termination; however, we do not detect these signals in the preceding shifts. Our results have important implications for detecting tipping points in palaeoclimate records outside glacial terminations.
Clim. Past Discuss., 11, 1313-1341, doi:10.5194/cpd-11-1313-2015, 2015
Arctic sea ice in the PlioMIP ensemble: is model performance for modern climates a reliable guide to performance for the past or the future?
Summary: Simulations of pre-industrial and Pliocene Arctic sea ice by eight GCMs are analysed. Ensemble variability of sea ice extent and thickness is greater in the Pliocene, particularly during the summer months. Weak correlations between pre-industrial sea ice and temperatures are suggested to be affected by model tuning, which along with comparisons to proxy data indicate that pre-industrial performance not necessarily a reliable guide to Pliocene performance for sea ice simulation.
Clim. Past Discuss., 11, 1263-1312, doi:10.5194/cpd-11-1263-2015, 2015
Quality assessment of chronologies in Latin American pollen records: a contribution to centennial to millennial scale studies of environmental change
Summary: We present a review of chronological dating from ca. 1100 fossil pollen records in Central and South America. Additionally, a temporal quality assessment is implemented on 292 records from northwest South-America, which include recalibrating 233 age models. This method evaluates uncertainties for inferred sample ages and chronologies. Important time windows on centennial-millennial climate variability are discussed for sample resolution (estimated years/sample) and temporal uncertainty.
Clim. Past Discuss., 11, 1219-1262, doi:10.5194/cpd-11-1219-2015, 2015
Short-term variability in the sedimentary BIT index of Lake Challa, East Africa over the past 2200 years: validating the precipitation proxy
Clim. Past Discuss., 11, 1177-1218, doi:10.5194/cpd-11-1177-2015, 2015
Parallelisms between sea surface temperature changes in the western tropical Atlantic (Guiana basin) and high latitude climate signals over the last 140 000 years
Summary: The alkenone sea surface temperatures in the Guiana basin show a rapid transmission of the climate variability from arctic-to-tropical latitudes during the last two interglacials (MIS1 and MIS5e) and warm long interstadials (MIS5d-a). In contrast, the abrupt variability of the glacial interval does not follow the North Atlantic climate but it is shaped by precessional changes. This arctic-to-tropical decoupling occurs when the Atlantic meridional overturning circulation is substantially reduced
Clim. Past Discuss., 11, 1143-1175, doi:10.5194/cpd-11-1143-2015, 2015
The simulated climate of the Last Glacial Maximum and the insights into the global carbon cycle
Summary: Global climate models provide an important tool for simulating the earth's climate. Here we present a simulation of the climate of the Last Glacial Maximum, which was obtained by setting atmospheric greenhouse gas concentrations and the earth's orbital parameters to the 21 000 years before present values. We simulate an ocean behaviour that agrees with paleoclimate reconstructions supporting our ability to model the climate system and use the model to explore the impacts on the carbon cycle.
Clim. Past Discuss., 11, 1093-1142, doi:10.5194/cpd-11-1093-2015, 2015
Terrestrial biosphere changes over the last 120 kyr and their impact on ocean δ 13C
Summary: In this paper we use two climate models to test how earth’s vegetation responded to changes in climate over the last 120 000 years, looking at warm interglacial climates like today, cold ice-age glacial climates, and intermediate climates. The models agree well with observations from pollen, showing smaller forested areas and larger desert areas during cold periods. Forests store most terrestrial carbon; the terrestrial carbon lost during cold climates was most likely relocated to the oceans.
Clim. Past Discuss., 11, 1031-1091, doi:10.5194/cpd-11-1031-2015, 2015
Radiative forcing by forest and subsequent feedbacks in the early Eocene climate
Clim. Past Discuss., 11, 997-1029, doi:10.5194/cpd-11-997-2015, 2015
Greenland Ice Sheet influence on Last Interglacial climate: global sensitivity studies performed with an atmosphere–ocean general circulation model
Summary: The Last Interglacial has been warmer with a reduced Greenland Ice Sheet (GIS) compared to the late Holocene. We analyse - through climate model simulations - the impact of a reduced GIS on the global surface air temperature and find a relatively strong warming especially in the Northern Hemisphere. These results are then compared to temperature reconstructions, indicating good agreement with respect to the pattern. However, the simulated temperatures underestimate the proxy-based temperatures.
Clim. Past Discuss., 11, 933-995, doi:10.5194/cpd-11-933-2015, 2015
Early-Holocene warming in Beringia and its mediation by sea-level and vegetation changes
Summary: The ongoing warming of the Arctic is producing changes in vegetation and hydrology, that coupled with rising sea level, could mediate the global changes. We explore this possibility using a regional climate-model simulations of a past interval of warming in Beringia, and found that the regional-scale changes do strongly mediate the responses to global changes, amplifying them in some cases, damping them in others, and, overall, generating considerable spatial heterogeneity in climate change.
Clim. Past Discuss., 11, 873-932, doi:10.5194/cpd-11-873-2015, 2015
Optimal Ranking Regime analysis of TreeFlow dendrohydrological reconstructions
Summary: A new approach to time series analysis - the ORR method- was used to evaluate reconstructed western U.S. streamflow records during 1500-2007. This method shows an interesting pattern of alternating drought and wet periods during the late 16th and 17th centuries, a period with relatively few drought or wet periods during the 18th century, and the and the reappearance of alternating dry and wet periods during the 19th and early 20th centuries.
Clim. Past Discuss., 11, 755-803, doi:10.5194/cpd-11-755-2015, 2015
Trace metal evidence for a poorly ventilated glacial Southern Ocean
Summary: Trace metal (Ag, Cd, Re, Mo) concentrations in glacial-age, Atlantic sector Southern Ocean sediments that are similar to those found in modern sediments underlying oxygen minimum zones (e.g., Eastern Pacific) imply that the glacial Southern Ocean was significantly less well ventilated than present. These data point to a glacial equivalent of Lower Circumpolar Deep Water as the low-oxygen water mass, and the potential storage location of the ‘missing’ glacial CO2.
Clim. Past Discuss., 11, 637-670, doi:10.5194/cpd-11-637-2015, 2015
Coupled Northern Hemisphere permafrost-ice sheet evolution over the last glacial cycle
Summary: In this paper we explore the permafrost-ice sheet interaction using the fully coupled climate-ice sheet model CLIMBER-2 with the addition of a newly developed permafrost module. We find that permafrost has a moderate but significant effect on ice sheet dynamics during the last glacial cycle. In particular at the last glacial maximum the inclusion of permafrost leads to a 15 meter sea level equivalent increase in Northern Hemisphere ice volume when permafrost is included.
Clim. Past Discuss., 11, 555-601, doi:10.5194/cpd-11-555-2015, 2015
South-western Africa vegetation responses to atmospheric and oceanic changes during the last climatic cycle
Summary: We present a new pollen-based palaeoclimatic reconstruction covering the period between 190,000 and 24,000 years ago from a marine sediment core located off the Namibian coast. Our work identifies increased dryness during the three warmest periods of the last interglacial involving atmospheric and oceanic reorganizations in southern Africa that are linked to precession minima.
Clim. Past Discuss., 11, 345-376, doi:10.5194/cpd-11-345-2015, 2015
A~regional climate palaeosimulation for Europe in the period 1501–1990 – Part II: Comparison with gridded reconstructions
Clim. Past Discuss., 11, 307-343, doi:10.5194/cpd-11-307-2015, 2015