Chicxulub's Impact Caused "Nuclear" Winter in New Jersey

Evidence for Cretaceous-Paleogene boundary bolide "impact winter" conditions from New Jersey, USA

Authors:

Vellekoop et al

Abstract:

Abrupt and short-lived "impact winter" conditions have commonly been implicated as the main mechanism leading to the mass extinction at the Cretaceous-Paleogene (K-Pg) boundary (ca. 66 Ma), marking the end of the reign of the non-avian dinosaurs. However, so far only limited evidence has been available for such a climatic perturbation. Here we perform high-resolution TEX86 organic paleothermometry on three shallow cores from the New Jersey paleoshelf, (northeastern USA) to assess the impact-provoked climatic perturbations immediately following the K-Pg impact and to place these short-term events in the context of long-term climate evolution. We provide evidence of impact-provoked, severe climatic cooling immediately following the K-Pg impact. This so-called "impact winter" occurred superimposed on a long-term cooling trend that followed a warm phase in the latest Cretaceous.

Human Caused Global Warming has Postponed the Next Glacial Cycle by at Least 50,000 Years

Humanity has become a geological force that is able to suppress the beginning of the next ice age, a study now published in the renowned scientific journal Nature shows. Cracking the code of glacial inception, scientists of the Potsdam Institute for Climate Impact Research found the relation of insolation and CO2 concentration in the atmosphere to be the key criterion to explain the last eight glacial cycles in Earth history. At the same time their results illustrate that even moderate human interference with the planet's natural carbon balance might postpone the next glacial inception by 100.000 years.

"Even without man-made climate change we would expect the beginning of a new ice age no earlier than in 50.000 years from now - which makes the Holocene as the present geological epoch an unusually long period in between ice ages," explains lead author Andrey Ganopolski. "However, our study also shows that relatively moderate additional anthropogenic CO2-emissions from burning oil, coal and gas are already sufficient to postpone the next ice age for another 50.000 years. The bottom line is that we are basically skipping a whole glacial cycle, which is unprecedented. It is mind-boggling that humankind is able to interfere with a mechanism that shaped the world as we know it."

For the first time, research can explain the onset of the past eight ice ages by quantifying several key factors that preceded the formation of each glacial cycle. "Our results indicate a unique functional relationship between summer insolation and atmospheric CO2 for the beginning of a large-scale ice-sheet growth which does not only explain the past, but also enables us to anticipate future periods when glacial inception might occur again," Ganopolski says.

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Evidence of Orbital Climate Forcing at the Triassic/Jurassic Boundary

Triassic–Jurassic climate in continental high-latitude Asia was dominated by obliquity-paced variations (Junggar Basin, Ürümqi, China)

Authors:

Sha et al

Abstract:

Empirical constraints on orbital gravitational solutions for the Solar System can be derived from the Earth’s geological record of past climates. Lithologically based paleoclimate data from the thick, coal-bearing, fluvial-lacustrine sequences of the Junggar Basin of Northwestern China (paleolatitude ∼60°) show that climate variability of the warm and glacier-free high latitudes of the latest Triassic–Early Jurassic (∼198–202 Ma) Pangea was strongly paced by obliquity-dominated (∼40 ky) orbital cyclicity, based on an age model using the 405-ky cycle of eccentricity. In contrast, coeval low-latitude continental climate was much more strongly paced by climatic precession, with virtually no hint of obliquity. Although this previously unknown obliquity dominance at high latitude is not necessarily unexpected in a high CO2 world, these data deviate substantially from published orbital solutions in period and amplitude for eccentricity cycles greater than 405 ky, consistent with chaotic diffusion of the Solar System. In contrast, there are indications that the Earth–Mars orbital resonance was in today’s 2-to-1 ratio of eccentricity to inclination. These empirical data underscore the need for temporally comprehensive, highly reliable data, as well as new gravitational solutions fitting those data.

Orbital Climate Forcing at the Calymmian/Ectasian MesoProterozoic Boundary

Orbital forcing of climate 1.4 billion years ago

Authors:

Zhang et al

Abstract:

Fluctuating climate is a hallmark of Earth. As one transcends deep into Earth time, however, both the evidence for and the causes of climate change become difficult to establish. We report geochemical and sedimentological evidence for repeated, short-term climate fluctuations from the exceptionally well-preserved ∼1.4-billion-year-old Xiamaling Formation of the North China Craton. We observe two patterns of climate fluctuations: On long time scales, over what amounts to tens of millions of years, sediments of the Xiamaling Formation record changes in geochemistry consistent with long-term changes in the location of the Xiamaling relative to the position of the Intertropical Convergence Zone. On shorter time scales, and within a precisely calibrated stratigraphic framework, cyclicity in sediment geochemical dynamics is consistent with orbital control. In particular, sediment geochemical fluctuations reflect what appear to be orbitally forced changes in wind patterns and ocean circulation as they influenced rates of organic carbon flux, trace metal accumulation, and the source of detrital particles to the sediment.

Does Undersea Volcanic Activity Affect Climate on 100,000 Year Cycle?

The intensity of volcanic activity at deeply submerged mid-ocean ridges waxes and wanes on a roughly 100,000-year cycle, according to a new study that might help explain poorly understood variations in Earth's climate that occur on approximately the same timetable.

Cyclical variations in Earth's tilt and orbit--occurring at 23,000-, 41,000- and 100,000-year intervals--are known to strongly influence our planet's long-term climate. They are associated with the coming and going of ice ages that also takes place about every 100,000 years.

In particular, changes in the roundness of Earth's orbit around the Sun unfold on approximately the same 100,000 year cycle as the planet's global swings between icy and temperate conditions. But, the variation in solar radiation reaching Earth due to temporarily larger and smaller distances between our planet and the Sun can't fully explain the magnitude of the climatic shifts.

The new research finds evidence in the profile of sea-floor elevation that volcanic activity at mid-ocean ridges, where molten rock emerges from Earth's interior and creates new planetary crust, coincides with these 100,000-year changes in Earth's orbit and climate. Given that volcanic eruptions release the climate-altering gas carbon-dioxide, significant emissions of the gas might take place during upswings of undersea volcanic activity, potentially affecting the climate at 100,000-year intervals.

"Generally, mid-ocean ridges are thought of as this tiny, not very significant contributor to the carbon cycle and that is true, but that's because they are thought of as a steady-state process. But, if they go through periods of significantly enhanced volcanism and significantly suppressed volcanism, then they may be more important than we thought," said Maya Tolstoy, an associate professor at Lamont-Doherty Earth Observatory at Columbia University in New York and sole author of the new study accepted for publication in Geophysical Research Letters, a journal of the American Geophysical Union.

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The Link Between Tectonics & Climate in Miocene Neogene Asian Interior's Aridification

Late Miocene stepwise aridification in the Asian interior and the interplay between tectonics and climate

Authors:

Sun et al

Abstract:

The mid-latitudinal central Asian continent is characterized by large sand deserts and Gobi (stony desert). In this context, it is of interest to study the timing and forcing mechanisms of aridification in the region. Here we present multiple geochemical climatic proxies from late Cenozoic strata in the Tarim Basin of northwestern China, a region sensitive to climatic change. The results yield long-term climatic records covering a time interval of 13.3 to 2.5 Ma. We find that a general trend towards a dry climate was superimposed by two stepwise aridification events, the first lesser aridity phase occurred at ~ 7–5.3 Ma and the second extreme aridity episode was initiated at ~ 5.3 Ma. Based on the correlation between climatic change and regional tectonic events, we propose a mechanism to explain the climatic variations. The general long-term drying trend since the mid-Miocene was a response to global climatic cooling, while the stepwise aridification since the latest Miocene was controlled mainly by regional tectonic uplift.

Sensivity of Late Miocene Neogene Paleoclimate to Carbon dioxide Forcing

Disentangling the roles of late Miocene palaeogeography and vegetation – Implications for climate sensitivity

Authors:

Bradshaw et al

Abstract:

The impact of rising CO2 on future climate remains uncertain but the evidence for high CO2 in the palaeorecord suggests that past climates could provide a potentially quantifiable indication of climate in a high-CO2 world. One such past time period is the late Miocene (11.6–5.3 Ma), for which CO2 reconstructions indicate higher levels than those of preindustrial, and similar to the present atmospheric level (~ 400 ppm). The late Miocene palaeorecord suggests a much warmer and wetter Northern Hemisphere than preindustrial. However, vegetation feedbacks are an important component of the climate system and vegetation distribution reconstructions from the palaeorecord have been shown to be very different to the present vegetation distribution. We examine the roles that different vegetation and palaeogeography play in climate sensitivity for the late Miocene and consider the implications for potential future climate change. To do this we use coupled atmosphere-ocean-vegetation simulations of late Miocene and potential modern climates forced by three different CO2 concentrations with vegetation perturbation experiments and make quantitative comparisons to the palaeorecord. Optimal regions to target late Miocene palaeodata acquisition for the purposes of informing about future climate include North America, northern Africa, Australia, Paraguay and southern Brazil, and northeastern Asia. These regions are those which the model results predict to be most sensitive to CO2 forcing, but where the local temperature response to CO2 forcing is similar between the simulated potential modern and late Miocene climates. The model results suggest that climate sensitivity to CO2 forcing is directly affected by the palaeogeographic configuration and that the inferred climate sensitivity for doubled CO2 is 0.5–0.8 °C higher for the late Miocene than we might expect for future climate because of differences in synergy. The greater land mass at high northern latitudes during the late Miocene and the differences in vegetation distribution predictions that result, combined with differences in ocean circulation and the effect of sea ice, make the late Miocene boundary conditions more sensitive to CO2 forcing than the modern boundary conditions.

Volcanic Climate Forcing Stronger Than Expected

Total volcanic stratospheric aerosol optical depths and implications for global climate change

Authors:

Ridley et al

Abstract:

Understanding the cooling effect of recent volcanoes is of particular interest in the context of the post-2000 slowing of the rate of global warming. Satellite observations of aerosol optical depth (AOD) above 15 km have demonstrated that small-magnitude volcanic eruptions substantially perturb incoming solar radiation. Here we use lidar, AERONET and balloon-borne observations to provide evidence that currently available satellite databases neglect substantial amounts of volcanic aerosol between the tropopause and 15 km at mid to high latitudes, and therefore underestimate total radiative forcing resulting from the recent eruptions. Incorporating these estimates into a simple climate model, we determine the global volcanic aerosol forcing since 2000 to be −0.19 ± 0.09 Wm−2. This translates into an estimated global cooling of 0.05 to 0.12 °C. We conclude that recent volcanic events are responsible for more post-2000 cooling than is implied by satellite databases that neglect volcanic aerosol effects below 15 km.

erm? A Recovered 100-million Year History of the Carbon Cycle is Accurate?

A 100-million year history of the carbon cycle based on the 400-kyr cycle in marine δ13C benthic records

Authors:

Pallard et al

Abstract:

Documenting the past co-evolution of Earth temperatures and of the carbon cycle is of paramount importance for our understanding of climate dynamics. Atmospheric CO2 is well constrained over the last million years through direct measurements in air bubbles from Antarctic ice cores. For older times, many different and sometimes conflicting proxies have been suggested. Here, we provide a new methodology to constrain the carbon cycle in the past, based on marine benthic δ13C records. Marine δ13C data is recording a persistent 400-kyr cycle, with an amplitude primarily linked to the total amount of carbon in the ocean, or dissolved inorganic carbon (DIC). By extracting this amplitude from published records, we obtain a new strong constraint on the 100-million year history of Earth's carbon cycle. The obtained Cenozoic evolution of DIC is in surprisingly good agreement with existing reconstructions of pCO2, suggesting that pCO2 is mostly driven by DIC changes over this period. In contrast, we find no strong decreasing trend in DIC between the Cretaceous and the Cenozoic, suggesting that Cretaceous atmospheric pCO2 levels were limited, and high temperatures at this time should be explained by other mechanisms. Alternatively, high Cretaceous atmospheric pCO2 could occur as a consequence of changes in oceanic chemistry, but not carbon content.

Does Short Term GeoEngineering Really Help With Climate Change?

Disentangling the effects of CO2 and short-lived climate forcer mitigation

Authors:

Rogelj et al

Abstract:

Anthropogenic global warming is driven by emissions of a wide variety of radiative forcers ranging from very short-lived climate forcers (SLCFs), like black carbon, to very long-lived, like CO2. These species are often released from common sources and are therefore intricately linked. However, for reasons of simplification, this CO2–SLCF linkage was often disregarded in long-term projections of earlier studies. Here we explicitly account for CO2–SLCF linkages and show that the short- and long-term climate effects of many SLCF measures consistently become smaller in scenarios that keep warming to below 2 °C relative to preindustrial levels. Although long-term mitigation of methane and hydrofluorocarbons are integral parts of 2 °C scenarios, early action on these species mainly influences near-term temperatures and brings small benefits for limiting maximum warming relative to comparable reductions taking place later. Furthermore, we find that maximum 21st-century warming in 2 °C-consistent scenarios is largely unaffected by additional black-carbon-related measures because key emission sources are already phased-out through CO2 mitigation. Our study demonstrates the importance of coherently considering CO2–SLCF coevolutions. Failing to do so leads to strongly and consistently overestimating the effect of SLCF measures in climate stabilization scenarios. Our results reinforce that SLCF measures are to be considered complementary rather than a substitute for early and stringent CO2 mitigation. Near-term SLCF measures do not allow for more time for CO2 mitigation. We disentangle and resolve the distinct benefits across different species and therewith facilitate an integrated strategy for mitigating both short and long-term climate change.

Increased Arctic Planet Growth Increases High Latitude Warming

Increased carbon dioxide in the atmosphere is known to boost vegetation cover at high latitudes — and this could accelerate Arctic warming year-round.

Grasses and shrubs have a warming effect because plant-covered areas reflect less sunlight than barren surfaces do. Baek-Min Kim at the Korea Polar Research Institute in Incheon, South Korea, Sang-Yoon Jun at the Korea Institute of Atmospheric Prediction Systems in Seoul and their colleagues used a climate model to study the impact of doubled CO2 concentrations and increased high-latitude plant growth on Arctic temperatures.

They found that increased vegetation in summer warms the surface and this heat moves to the Arctic, where it causes additional ocean warming and sea-ice melting in winter and spring. The exposed ocean then releases more heat, leading to a further boost in Arctic warming and promoting even more plant growth the following season, the team says.

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Nanodiamond-Rich Layer across Three Continents at the Younger Dryas Boundary

Nanodiamond-Rich Layer across Three Continents Consistent with Major Cosmic Impact at 12,800 Cal BP

Authors:

Kinzie et al

Abstract:

A major cosmic-impact event has been proposed at the onset of the Younger Dryas (YD) cooling episode at ≈12,800 ± 150 years before present, forming the YD Boundary (YDB) layer, distributed over greater than 50 million km2 on four continents. In 24 dated stratigraphic sections in 10 countries of the Northern Hemisphere, the YDB layer contains a clearly defined abundance peak in nanodiamonds (NDs), a major cosmic-impact proxy. Observed ND polytypes include cubic diamonds, lonsdaleite-like crystals, and diamond-like carbon nanoparticles, called n-diamond and i-carbon. The ND abundances in bulk YDB sediments ranged up to ≈500 ppb (mean: 200 ppb) and that in carbon spherules up to ≈3700 ppb (mean: ≈750 ppb); 138 of 205 sediment samples (67%) contained no detectable NDs. Isotopic evidence indicates that YDB NDs were produced from terrestrial carbon, as with other impact diamonds, and were not derived from the impactor itself. The YDB layer is also marked by abundance peaks in other impact-related proxies, including cosmic-impact spherules, carbon spherules (some containing NDs), iridium, osmium, platinum, charcoal, aciniform carbon (soot), and high-temperature melt-glass. This contribution reviews the debate about the presence, abundance, and origin of the concentration peak in YDB NDs. We describe an updated protocol for the extraction and concentration of NDs from sediment, carbon spherules, and ice, and we describe the basis for identification and classification of YDB ND polytypes, using nine analytical approaches. The large body of evidence now obtained about YDB NDs is strongly consistent with an origin by cosmic impact at ≈12,800 cal BP and is inconsistent with formation of YDB NDs by natural terrestrial processes, including wildfires, anthropogenesis, and/or influx of cosmic dust.

Evidence of Milankovitch Cycle Driven Climate Forcing From Eocene Paleogene Spain

Climate forcing of fine-grained deep-marine systems in an active tectonic setting: Middle Eocene, Ainsa Basin, Spanish Pyrenees

Authors:

Cantealejo et al

Abstract:

A multi-proxy approach to understand environmental change in deep time was undertaken on about 150 m of core from a 230 m-long Middle Eocene core from the Ainsa basin, Spanish Pyrenees, representing deep-marine siliciclastic sediments, using detailed sedimentary logging, high-resolution multi-element XRF geochemistry, total organic carbon, and stable carbon isotopes. The Well A6 was drilled, as part of an industry–university consortium, through siltstones, fine-/very fine-grained sandstone turbidites, and hemipelagic structureless mudstones, that were deposited as overbank and off-axis deposits from a sandy submarine fan, and interfan deposits. For comparative mineralogy between the sandstone turbidites and siltstones, scanning electron microscopy (SEM) and X-ray diffraction (XRD) were undertaken on selected samples. The sandstone turbidites show enrichment of detrital elements such as Si, Zr and Ti, that can be linked to greater quartz and heavy-mineral content compared with adjacent siltstones. Structureless hemipelagic mudstones comprise mainly clay minerals and carbonate. We interpret the sandstone turbidites as from hyperpycnal flows during high river sediment discharge, whilst hemipelagic mudstones resulted from the suspension fall-out of hypopycnal flows. Cyclostratigraphic analysis of the core reveals Milankovitch cyclicity at frequencies of ~ 0.03 cycles/m (short eccentricity), ~ 0.09 cycles/m (obliquity), ~ 0.15 cycles/m (precession couplet) and ~ 0.19 cycles/m (precession couplet). Orbital parameters appear to have controlled the cyclic delivery of coarser-grained sediment by turbidity currents. Two equally plausible depositional models, both as Milankovitch-driven, can explain the cyclical changes in the deep-marine sediments: (1) climatic cycles, with humid periods of enhanced chemical weathering, increased storminess and greater riverine run-off, leading to high sediment flux to the deep basin as sandstone turbidites; (2) climatic cycles, with cooler conditions linked to high-frequency small-scale eustatic sea-level fluctuations, with lowstand shelf-edge delta progradation, resulting in greater volumes of coarse detrital sediment to the seafloor by hyperpycnal flows. This study provides an insight into the likely depositional effects of orbitally-induced climate change on the nature and delivery of terrigenous sediment into deep-marine environments.

Did an Injection of Fresh Water in the Labrador Sea Help Trigger the Little Ice Age?

Surface changes in the Eastern Labrador Sea around the onset of the Little Ice Age

Authors:

Moffa-Sánchez et al

Abstract:

Despite the relative climate stability of the present interglacial, it has been punctuated by several centennial time scale climatic oscillations, the latest of which are often colloquially referred to as the Medieval Climatic Anomaly (MCA) and the Little Ice Age (LIA). The most favored explanation for the cause of these anomalies is that they were triggered by variability in solar irradiance and/or volcanic activity and amplified by ocean-atmosphere-sea ice feedbacks. As such, changes in the strength of the Atlantic Meridional Overturning Circulation (AMOC) are widely believed to have been involved in the amplification of such climatic oscillations. The Labrador Sea is a key area of deep water formation. The waters produced here contribute approximately one-third of the volume transport of the deep limb of the AMOC and drive changes in the North Atlantic surface hydrography and subpolar gyre circulation. In this study, we present multi-proxy reconstructions from a high-resolution marine sediment core located south of Greenland that suggest an increase in the influence of polar waters reaching the Labrador Sea close to MCA-LIA transition. Changes in freshwater forcing may have reduced the formation of Labrador Sea Water and contributed towards the onset of the LIA cooling.

Carbon Residence Time Dominates Future Climate Scenarios

Carbon residence time dominates uncertainty in terrestrial vegetation responses to future climate and atmospheric CO2

Authors:

Friend et al

Abstract:

Future climate change and increasing atmospheric CO2 are expected to cause major changes in vegetation structure and function over large fractions of the global land surface. Seven global vegetation models are used to analyze possible responses to future climate simulated by a range of general circulation models run under all four representative concentration pathway scenarios of changing concentrations of greenhouse gases. All 110 simulations predict an increase in global vegetation carbon to 2100, but with substantial variation between vegetation models. For example, at 4 °C of global land surface warming (510–758 ppm of CO2), vegetation carbon increases by 52–477 Pg C (224 Pg C mean), mainly due to CO2 fertilization of photosynthesis. Simulations agree on large regional increases across much of the boreal forest, western Amazonia, central Africa, western China, and southeast Asia, with reductions across southwestern North America, central South America, southern Mediterranean areas, southwestern Africa, and southwestern Australia. Four vegetation models display discontinuities across 4 °C of warming, indicating global thresholds in the balance of positive and negative influences on productivity and biomass. In contrast to previous global vegetation model studies, we emphasize the importance of uncertainties in projected changes in carbon residence times. We find, when all seven models are considered for one representative concentration pathway × general circulation model combination, such uncertainties explain 30% more variation in modeled vegetation carbon change than responses of net primary productivity alone, increasing to 151% for non-HYBRID4 models. A change in research priorities away from production and toward structural dynamics and demographic processes is recommended.

Precessional Forcing Remarkably Recored in Lower Maastrichtian Cretaceous Section in France

Lower Maastrichtian cyclostratigraphy of the Bidart section (Basque country, SW France): A remarkable record of precessional forcing

Authors:

Husson et al

Abstract:

Cyclostratigraphic analysis of the Maastrichtian limestone-marl alternations of Bidart (SW France) allows the hypothesis of orbital control on lithological cycles to be evaluated. Magnetic Susceptibility (MS), oxygen and carbon isotope measurements, sampled at a high resolution, are analyzed using various cyclostratigraphic tools. A statistically significant orbital signal is detected, with a remarkable record of the precession corresponding to the limestone-marl couplets. This well expressed orbital forcing allows the building of a relative cyclostratigraphic time scale for the MS and δ13C records based on the 100 kyr eccentricity cycle. The total duration of the section is estimated at 1.44 ± 0.22 Myr. Correlation based on calcareous nannofossil biostratigraphy and comparison of the scaled Bidart δ13C record to the astronomically calibrated δ13C signal of ODP hole 762C shows that the studied section extends from -71.5 to -70 Ma, covering the upper part of Chron C32n.1n and 2/3 of Chron C31r. Oxygen isotope data suggest a 2°C cooling of sea-surface temperatures during the studied interval. When placed on the long-term δ18O trend of the Bidart section, this interval is here recognized as the onset of the early Maastrichtian cooling event. With its excellent record of the precessional forcing, the Bidart section, along with other sections of the Basque country, is a useful tool for the refinement of the Maastrichtian timescale.

Miocene Cooling Tied to Increased Eastern Pacific Upwelling

Middle Miocene climate cooling linked to intensification of eastern equatorial Pacific upwelling

Authors:

Holbourn et al

Abstract:

During the Middle Miocene, Earth's climate transitioned from a relatively warm phase (Miocene climatic optimum) to a colder mode with reestablishment of permanent ice sheets on Antarctica, thus marking a fundamental step in Cenozoic cooling. Carbon sequestration and atmospheric CO2 drawdown through increased terrestrial and/or marine productivity have been proposed as the main drivers of this fundamental transition. We integrate high-resolution (1–3 k.y.) benthic stable isotope data with X-ray fluorescence scanner-derived biogenic silica and carbonate accumulation estimates in an exceptionally well preserved sedimentary archive, recovered at Integrated Ocean Drilling Program Site U1338, to reconstruct eastern equatorial Pacific productivity variations and to investigate temporal links between high- and low-latitude climate change over the interval 16–13 Ma. Our records show that the climatic optimum (16.8–14.7 Ma) was characterized by high-amplitude climate variations, marked by intense perturbations of the carbon cycle. Episodes of peak warmth at (Southern Hemisphere) insolation maxima coincided with transient shoaling of the carbonate compensation depth and enhanced carbonate dissolution in the deep ocean. A switch to obliquity-paced climate variability after 14.7 Ma concurred with a general improvement in carbonate preservation and the onset of stepwise global cooling, culminating with extensive ice growth over Antarctica ca. 13.8 Ma. We find that two massive increases in opal accumulation ca. 14.0 and ca. 13.8 Ma occurred just before and during the final and most prominent cooling step, supporting the hypothesis that enhanced siliceous productivity in the eastern equatorial Pacific contributed to CO2 drawdown.

Carbon Dioxide Emissions From United States Lowest Since 1994

Carbon dioxide emissions from energy production in the United States fell to 5.29 billion metric tons in 2012 - its lowest level since 1994 - despite a growing economy and rising population, according to government data released on Monday.

The Energy Information Administration, the statistics arm of the Department of Energy, said there was a 3.8 percent drop from the previous year.

That marked the largest decline in a non-recession year since EIA started tracking the data.

The latest decline came amid a large drop in energy intensity, the amount of energy consumed relative to GDP.

"The emissions decline was the largest in a year with positive growth in per capita output and the only year to show a decline where per capita output increased 2 percent or more," the EIA said.

Energy consumption fell 2.4 percent in 2012 from 2011 while GDP rose 2.8 percent.

In addition to reduced energy intensity, carbon dioxide emissions reflected lower residential sector demand for heating after a warmer-than-usual winter in 2012.

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Toba Didn't Do It to Us: No Sign of Volcanic Winter Induced in Sediment from African Lake

Ash from the Toba supereruption in Lake Malawi shows no volcanic winter in East Africa at 75 ka

Authors:

1. Christine S. Lane (a)
2. Ben T. Chorn (b)
3. Thomas C. Johnson (b)

Affiliations:

a. Research Laboratory for Archaeology and the History of Art, University of Oxford, Oxford OX1 3QY, United Kingdom; and

b. Large Lakes Observatory and Department of Geological Sciences, University of Minnesota, Duluth, MN 55812

Abstract:

The most explosive volcanic event of the Quaternary was the eruption of Mt. Toba, Sumatra, 75,000 y ago, which produced voluminous ash deposits found across much of the Indian Ocean, Indian Peninsula, and South China Sea. A major climatic downturn observed within the Greenland ice cores has been attributed to the cooling effects of the ash and aerosols ejected during the eruption of the Youngest Toba Tuff (YTT). These events coincided roughly with a hypothesized human genetic bottleneck, when the number of our species in Africa may have been reduced to near extinction. Some have speculated that the demise of early modern humans at that time was due in part to a dramatic climate shift triggered by the supereruption. Others have argued that environmental conditions would not have been so severe to have such an impact on our ancestors, and furthermore, that modern humans may have already expanded beyond Africa by this time. We report an observation of the YTT in Africa, recovered as a cryptotephra layer in Lake Malawi sediments, >7,000 km west of the source volcano. The YTT isochron provides an accurate and precise age estimate for the Lake Malawi paleoclimate record, which revises the chronology of past climatic events in East Africa. The YTT in Lake Malawi is not accompanied by a major change in sediment composition or evidence for substantial temperature change, implying that the eruption did not significantly impact the climate of East Africa and was not the cause of a human genetic bottleneck at that time.