Rapid Climate Transitions Research Articles

Asymmetry of AMOC Hysteresis in a State‐Of‐The‐Art Global Climate Model

AbstractWe study hysteresis properties of the Atlantic Meridional Overturning Circulation (AMOC) under a slowly‐varying North Atlantic (20°N–50°N) freshwater flux forcing in state‐of‐the‐art global climate model (GCM), the Community Earth System Model. Results are presented of a full hysteresis simulation (4,400 model years) and show that there is a hysteresis width of about 0.4 Sv. This demonstrates that an AMOC collapse and recovery do not only occur in conceptual and idealized climate models, but also in a state‐of‐the‐art GCM. The AMOC recovery is about a factor six faster than the AMOC collapse and this asymmetry is due to the major effect of the North Atlantic sea‐ice distribution on the AMOC recovery. The results have implications for projections of possible future AMOC behavior and for explaining relatively rapid climate transitions in the geological past.

Are rapid and inclusive energy and climate transitions oxymorons? Towards principles of responsible acceleration

Building from two strands of literature within “Sociotechnical agendas: Reviewing future directions for energy and climate research”, this perspective piece seeks to open a discussion about how to responsibly accelerate transitions. First, we identify a managerial literature on how innovation and diffusion can be accelerated, which focuses on deliberation with consensus-oriented ambitions. Second, is a set of perspectives that highlights unevenness, and therefore seeks to radically expand climate and energy democracy by promoting new forms of participatory practices. There are few contact points between these literatures. We argue that this can be explained by tensions and paradoxes that accompany accelerated transitions. These paradoxes cannot easily be resolved. We discuss how accelerated social and technological change poses challenges to inclusive and participatory transitions. Further, we discuss how rapid transitions tends to contribute to conflicts between core and peripheral sites. Thus, transitions are not only affected by societal conditions, but also contribute to co-producing social order, including the many forms of social turmoil currently experienced. Such insight places greater responsibilities on transition scholars, especially from reflexive disciplines such as STS and geography. We conclude by discussing how this responsibility could translate into situating climate and energy transition scholarship in broader debates about future socio-technical orders, and sketch three principles of responsible acceleration: a) Moving towards a broad epistemic basis for producing and assessing transition policies and strategies, b) Nurturing polycentrism for rapid climate and energy transitions, and c) Developing polytemporal strategies for transition.

Using the past to inform the future

Paleoecology The late Quaternary paleorecord, within the past ∼130,000 years, can help to inform present-day management of the Earth's ecosystems and biota under climate change. Fordham et al. review when and where rapid climate transitions can be found in the paleoclimate record. They show how such events in Earth's history can shape our understanding of the consequences of future global warming, including rates of biodiversity loss, changes in ecosystem structure and function, and degradation in the goods and services that these ecosystems provide to humanity. They also highlight how recent developments at the intersection of paleoecology, paleoclimatology, and macroecology can provide opportunities to anticipate and manage the responses of species and ecosystems to changing climates in the Anthropocene. Science , this issue p. [eabc5654][1] [1]: /lookup/doi/10.1126/science.abc5654

Timing of the first drainage of the Baltic Ice Lake synchronous with the onset of Greenland Stadial 1

Glacial varves can give significant insights into recession and melting rates of decaying ice sheets. Moreover, varve chronologies can provide an independent means of comparison to other annually resolved climatic archives, which ultimately help to assess the timing and response of an ice sheet to changes across rapid climate transitions. Here we report a composite 1257‐year‐long varve chronology from southeastern Sweden spanning the regional late Allerød–late Younger Dryas pollen zone. The chronology was correlated to the Greenland Ice‐Core Chronology 2005 using the time‐synchronous Vedde Ash volcanic marker, which can be found in both successions. For the first time, this enables secure placement of the Lateglacial Swedish varve chronology in absolute time. Geochemical analysis from new varve successions indicate a marked change in sedimentation regime accompanied by an interruption of ice‐rafted debris deposition synchronous with the onset of Greenland Stadial 1 (GS‐1; 12 846 years before AD 1950). With the support of a simple ice‐flow/calving model, we suggest that slowdown of sediment transfer can be explained by ice‐sheet margin stabilization/advance in response to a significant drop of the Baltic Ice Lake level. A reassessment of chronological evidence from central‐western and southern Sweden further supports the hypothesis of synchronicity between the first (penultimate) catastrophic drainage of the Baltic Ice Lake and the start of GS‐1 in Greenland ice‐cores. Our results may therefore provide the first chronologically robust evidence linking continental meltwater forcing to rapid atmosphere–ocean circulation changes in the North Atlantic.

Abrupt glacial climate shifts controlled by ice sheet changes.

During glacial periods of the Late Pleistocene, an abundance of proxy data demonstrates the existence of large and repeated millennial-scale warming episodes, known as Dansgaard-Oeschger (DO) events. This ubiquitous feature of rapid glacial climate change can be extended back as far as 800,000 years before present (BP) in the ice core record, and has drawn broad attention within the science and policy-making communities alike. Many studies have been dedicated to investigating the underlying causes of these changes, but no coherent mechanism has yet been identified. Here we show, by using a comprehensive fully coupled model, that gradual changes in the height of the Northern Hemisphere ice sheets (NHISs) can alter the coupled atmosphere-ocean system and cause rapid glacial climate shifts closely resembling DO events. The simulated global climate responses--including abrupt warming in the North Atlantic, a northward shift of the tropical rainbelts, and Southern Hemisphere cooling related to the bipolar seesaw--are generally consistent with empirical evidence. As a result of the coexistence of two glacial ocean circulation states at intermediate heights of the ice sheets, minor changes in the height of the NHISs and the amount of atmospheric CO2 can trigger the rapid climate transitions via a local positive atmosphere-ocean-sea-ice feedback in the North Atlantic. Our results, although based on a single model, thus provide a coherent concept for understanding the recorded millennial-scale variability and abrupt climate changes in the coupled atmosphere-ocean system, as well as their linkages to the volume of the intermediate ice sheets during glacials.

Climate refugia: from the Last Glacial Maximum to the twenty‐first century

Climate refugia: from the Last Glacial Maximum to the twenty‐first century

Barents Sea inflow shutdown: A new mechanism for rapid climate changes

A new mechanism for rapid climate transitions in the high latitudes is presented which involves complex ocean‐sea ice‐atmosphere interactions. A shutdown of the Barents Sea Inflow (BSI) which carries a vast amount of heat into the Arctic Ocean is at the heart of the mechanism. The BSI shutdown is studied in a multi‐millennium integration with a global climate model forced by periodically (1000 yr) varying solar constant (±2 W/m2). A positive feedback between the inflow and sea ice cover is revealed in the model, which triggers rapid climate changes. The BSI shutdown events are associated with strong cooling in the northern latitudes and subsequent rearrangement of the Arctic Ocean surface current system. The results reveal the existence of a bifurcation point in the Arctic climate system and demonstrate that rapid climate transitions may be caused by local feedbacks and restricted to confined areas without significant global impacts.

The ‘flickering switch’ of late Pleistocene climate change revisited

Extremely rapid fluctuations observed in records of electrical conductivity measurements (ECM) from Greenland ice‐cores provoked the idea that the climate system may be capable of flickering between two states during rapid climate transitions. Here it is shown that in general, the flickers seen in ECM records probably reflect the highly non‐linear response of electrical conductivity as ice approaches acid/base neutrality, rather than significant changes in the climate system. High frequency, relatively low amplitude changes in chemistry, superimposed upon the broader changes typical of climate transitions would be capable of producing the observed characteristics of ECM records. It must be stated that this result does not detract from the observation of extremely rapid changes in, for example, ice core chemistry and isotopes, which clearly demonstrate that Earth's climate is capable of very rapid and major reorganisations.

On the origin and timing of rapid changes in atmospheric methane during the Last Glacial Period

We present high resolution records of atmospheric methane from the GISP2 (Greenland Ice Sheet Project 2) ice core for four rapid climate transitions that occurred during the past 50 ka: the end of the Younger Dryas at 11.8 ka, the beginning of the Bølling‐Allerød period at 14.8 ka, the beginning of interstadial 8 at 38.2 ka, and the beginning of interstadial 12 at 45.5 ka. During these events, atmospheric methane concentrations increased by 200–300 ppb over time periods of 100–300 years, significantly more slowly than associated temperature and snow accumulation changes recorded in the ice core record. We suggest that the slower rise in methane concentration may reflect the timescale of terrestrial ecosystem response to rapid climate change. We find no evidence for rapid, massive methane emissions that might be associated with large‐scale decomposition of methane hydrates in sediments. With additional results from the Taylor Dome Ice Core (Antarctica) we also reconstruct changes in the interpolar methane gradient (an indicator of the geographical distribution of methane sources) associated with some of the rapid changes in atmospheric methane. The results indicate that the rise in methane at the beginning of the Bølling‐Allerød period and the later rise at the end of the Younger Dryas were driven by increases in both tropical and boreal methane sources. During the Younger Dryas (a 1.3 ka cold period during the last deglaciation) the relative contribution from boreal sources was reduced relative to the early and middle Holocene periods.

Abrupt onset and termination of the African Humid Period:: rapid climate responses to gradual insolation forcing

A detailed (ca. 100 yr resolution) and well-dated (18 AMS 14 C dates to 23 cal. ka BP) record of latest Pleistocene–Holocene variations in terrigenous (eolian) sediment deposition at ODP Site 658C off Cap Blanc, Mauritania documents very abrupt, large-scale changes in subtropical North African climate. The terrigenous record exhibits a well-defined period of low influx between 14.8 and 5.5 cal. ka BP associated with the African Humid Period, when the Sahara was nearly completely vegetated and supported numerous perennial lakes; an arid interval corresponding to the Younger Dryas Chronozone punctuates this humid period. The African Humid Period has been attributed to a strengthening of the African monsoon due to gradual orbital increases in summer season insolation. However, the onset and termination of this humid period were very abrupt, occurring within decades to centuries. Both transitions occurred when summer season insolation crossed a nearly identical threshold value, which was 4.2% greater than present. These abrupt climate responses to gradual insolation forcing require strongly non-linear feedback processes, and current coupled climate model studies invoke vegetation and ocean temperature feedbacks as candidate mechanisms for the non-linear climate sensitivity. The African monsoon climate system is thus a low-latitude corollary to the bi-stable behavior of high-latitude deep ocean thermohaline circulation, which is similarly capable of rapid and large-amplitude climate transitions.

Warm climate transitions: A general circulation modeling study of the Late Paleocene Thermal Maximum (∼56 Ma)

A unique opportunity to study rapid climate transitions in a warm climate world is provided by the Late Paleocene Thermal Maximum (LPTM), a ∼100,000 year interval during which high‐latitude temperatures suddenly rose to their highest levels in the Cenozoic. In order to explore the processes and feedbacks which may have generated or limited this brief warming event, we model the atmosphere in equilibrium with sea surface temperatures (SSTs) derived for LPTM and for conditions more representative of the late Paleocene or early Eocene. Our model results suggest that conditions during the LPTM were more equable relative to the late Paleocene or early Eocene, with the mean annual temperature range reduced by more than 5°C over much of the continental interiors and precipitation over land increased by 5–10%. Nevertheless, despite specifying warm polar SSTs which exclude sea‐ice, the model produces January continental interior temperatures less than −13°C, in contrast to proxy data estimates of higher temperatures. The zonal wind strength is drastically reduced during the LPTM, and during Northern Hemisphere winter, deep atmospheric convection over the Arctic Sea is generated owing to the specified warm SSTs. We calculate substantial wind‐driven ocean circulation response to model‐produced wind fields for these time intervals, including increases in inferred western boundary current strength of 8–28%. In general, our results are in agreement with deep‐sea sediment‐derived clay and eolian records which suggest warm, wet conditions with less vigorous atmospheric circulation during these time periods. However, major changes in the high‐latitude hydrological cycle found in our LPTM experiment results raise important questions about high‐latitude stable isotopic paleoclimate interpretations.

Sudden climate transitions during the Quaternary

The time span of the past few million years has been punctuated by many rapid climate transitions, most of them on timescales of centuries to decades. The most detailed information is available for the Younger Dryas-to-Holocene stepwise change around 11 500 years ago, which seems to have occurred over a few decades. The speed of this change is probably representative of similar but less well studied climate transitions during the last few hundred thousand years. These include sudden cold events (Heinrich events/stadials), warm events (interstadials) and the beginning and ending of long warm phases, such as the Eemian interglacial. Detailed analysis of terrestrial and marine records of climate change will, however, be necessary before we can say confidently on what timescale these events occurred; they almost certainly did not take longer than a few centuries. Various mechanisms, involving changes in ocean circulation and biotic productivity, changes in atmospheric concentrations of greenhouse gases and haze particles, and changes in snow and ice cover, have been invoked to explain sudden regional and global transitions. We do not know whether such changes could occur in the near future as a result of human effects on climate. Phenomena such as the Younger Dryas and Heinrich events might only occur in a ‘glacial’ world with much larger ice sheets and more extensive sea-ice cover. A major sudden cold event, however, did probably occur under global climate conditions similar to those of the present, during the Eemian interglacial around 122 000 years ago. Less intensive, but significant rapid climate changes also occurred during the present (Holocene) interglacial, with cold and dry phases occurring on a 1500-year cycle, and with climate transitions on a decade-to-century timescale. In the past few centuries, smaller transitions (such as the ending of the Little Ice Age at about AD 1650) probably occurred over only a few decades at most. All evidence indicates that long-term climate change occurs in sudden jumps rather than incremental changes.

Sudden climate transitions during the Quaternary

The time span of the past few million years has been punctuated by many rapid climate transitions, most of them on timescales of centuries to decades. The most detailed information is available for the Younger Dryas-to-Holocene stepwise change around 11 500 years ago, which seems to have occurred over a few decades. The speed of this change is probably representative of similar but less well studied climate transitions during the last few hundred thousand years. These include sudden cold events (Heinrich events/stadials), warm events (interstadials) and the beginning and ending of long warm phases, such as the Eemian interglacial. Detailed analysis of terrestrial and marine records of climate change will, however, be necessary before we can say confidently on what timescale these events occurred; they almost certainly did not take longer than a few centuries.Various mechanisms, involving changes in ocean circulation and biotic productivity, changes in atmospheric concentrations of greenhouse gases and haze particles, and changes in snow and ice cover, have been invoked to explain sudden regional and global transitions. We do not know whether such changes could occur in the near future as a result of human effects on climate. Phenomena such as the Younger Dryas and Heinrich events might only occur in a ‘glacial’ world with much larger ice sheets and more extensive sea-ice cover. A major sudden cold event, however, did probably occur under global climate conditions similar to those of the present, during the Eemian interglacial around 122 000 years ago. Less intensive, but significant rapid climate changes also occurred during the present (Holocene) interglacial, with cold and dry phases occurring on a 1500-year cycle, and with climate transitions on a decade-to-century timescale. In the past few centuries, smaller transitions (such as the ending of the Little Ice Age at about AD 1650) probably occurred over only a few decades at most. All evidence indicates that long-term climate change occurs in sudden jumps rather than incremental changes.

Electrical measurements on the Greenland Ice Sheet Project 2 Core

The Greenland Ice Sheet Project 2 (GISP2) electrical conductivity measurement (ECM) record is an indication of the concentration of H + in the core. The ECM detected seasonal variations in the nitrate concentration of the core which were used to assist in dating the core by annual layer counting. Volcanic eruptions that produce acidic aerosols are recorded in the ECM record. Evidence of biomass burning is detected by the ECM because fire‐related ammonium emissions neutralize the acids in the core. Rapid climate transitions associated with the Younger Dryas and Dansgaard/Oeschger interstadial events alter the concentration of alkaline dust and are detected by the ECM. The ECM has been used to develop stratigraphic ties between the GISP2 and the Greenland Ice Core Project cores. Users of the data should be aware of some instrument‐related artifacts in the ECM record.

Rapid climate transitions in a coupled ocean–atmosphere model

RECENT geochemical data1,2 have challenged the view that rapid climate fluctuations in the North Atlantic at the end of the last glacial were caused by the thermohaline circulation of the ocean being switched 'on' or 'off'. Instead, these data suggest that the circulation pattern must have switched between a warm, deep mode and a cold, shallow mode, probably associated with different sites of deep convection3. Here I present simulations with a three-dimensional ocean model, coupled to an idealized atmosphere, which show this kind of transition. The mechanism for the transition is a rearrangement of convection in the North Atlantic, triggered by a brief freshwater pulse. This results in a drop in sea surface temperature in the North Atlantic by up to 5 °C within less than 10 years. The rate of North Atlantic Deep Water (NADW) forma-tion is the same in the cold climate as in the warm climate, but NADW sinks to intermediate depths only, while Antarctic Bottom Water pushes north to fill the entire abyssal Atlantic.

Global and local influences on the chemical composition of snowfall at Dye 3, Greenland: the record between 10 ka B.P. and 40 ka B.P.

Wisconsin Age ice from Dye 3, Greenland, shows a number of δ 18O level changes which indicate the occurrence of rapid climate transitions. In order to study the effect of climate change on geochemical fluxes we have selected several of these transitions for chemical analysis. At each transition we have measured chloride, nitrate and sulfate concentrations with 5 cm depth resolution. All three anionic species show significant variations which correlate with the measured δ 18O shifts. In general, periods of high δ 18O (warm periods) have lower anion concentrations than adjacent periods of low δ 18O (cold periods). However, the relative concentration shifts are not the same for all species, indicating that the concentration variations cannot be caused only by changes in snow accumulation rate acting on a constant anion flux. In addition to these rapid concentration changes, over the last 40 ka slower, secular variations in baseline concentrations also occurred. Baseline chloride and sulfate concentrations reached maxima near time of maximum ice volume. Baseline nitrate, on the other hand, remained relatively constant until near the end of the glaciation when its concentration rose. If a constant sulfate flux is assumed, the measured sulfate concentrations imply a dependence of snow accumulation rate on δ 18O for the Wisconsin which is similar to that presently observed in Greenland. The sulfate concentrations would then suggest that Wisconsin snowfall rates were, at times, as much as eight times lower than today.