The response of glaciers to climatic persistence

Roe, Gerard H.; Baker, M.

doi:10.1017/jog.2016.4

Cited by 20 publications

(34 citation statements)

References 53 publications

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“…The effects of persistence are dramatic: for both S or Ω forcing, 4 yr AR-1 persistence more than doubles σ L compared to length fluctuations driven by white forcing, and both 20 yr AR-1 and power-law persistence cause a ∼5-to-6-fold increase in σ L . This is consistent with the approximate proportionality between σ 2 L and τ AR1 predicted by theory (see, e.g., Roe and Baker, 2016;Robel et al, 2019). The power spectra of the forcings and responses show why persistence has such a strong effect.…”

supporting

confidence: 89%

“…While the comparisons above show that interior and terminus forcing elicit 275 different glacier responses due to the distinct geometries of the respective flux anomalies, we must also consider the possibility of climatic persistence in order to fully characterize an outlet glacier's response to natural climate variability. Roe and Baker (2016) showed that persistence in surface mass balance variability amplified the length fluctuations of mountain glaciers; we can expect similar principles to be especially relevant to outlet glaciers if they are sensitive to decade-scale ocean variability.…”

Section: Persistence In Variability 270mentioning

confidence: 84%

“…We generate timeseries following Percival et al (2001) and Roe and Baker (2016), first defining the desired spectral properties in frequency space, and then applying the same set of random phases to each case so that the resulting anomalies are correlated in the time domain. The power spectrum of a discrete AR-1 process as a function of frequency f , is…”

Section: Persistence In Variability 270mentioning

confidence: 99%

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The contrasting response of outlet glaciers to interior and ocean forcing

Christian¹,

Robel²,

Proistosescu³

et al. 2020

Preprint

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Abstract. The dynamics of marine-terminating outlet glaciers are of fundamental interest in glaciology, and affect mass loss from ice sheets in a warming climate. In this study, we analyze the response of outlet glaciers to different sources of climate forcing. We find that outlet glaciers have a characteristically different transient response to surface-mass-balance forcing applied over the interior than to oceanic forcing applied at the grounding line. A recently developed reduced model represents outlet glacier dynamics via two widely-separated response timescales: a fast response associated with grounding-zone dynamics, and a slow response of interior ice. The reduced model is shown to emulate the behavior of a more complex numerical model of ice flow. Together, these models demonstrate that ocean forcing first engages the fast, local response, and then the slow adjustment of interior ice, whereas surface-mass-balance forcing is dominated by the slow interior adjustment. We also demonstrate the importance of the timescales of stochastic forcing for assessing the natural variability of outlet glaciers, highlighting that decadal persistence in ocean variability can affect the behavior of outlet glaciers on centennial and longer timescales. Finally, we show that these transient responses have important implications for: attributing observed glacier changes to natural or anthropogenic influences; the future change already committed by past forcing; and the impact of past climate changes on the preindustrial glacier state, against which current and future anthropogenic influences are assessed.

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supporting

confidence: 89%

Section: Persistence In Variability 270mentioning

confidence: 84%

Section: Persistence In Variability 270mentioning

confidence: 99%

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The contrasting response of outlet glaciers to interior and ocean forcing

Christian¹,

Robel²,

Proistosescu³

et al. 2020

Preprint

View full text Add to dashboard Cite

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“…Though we have assumed that the noise forcing of ice shelf length includes no persistence in time (white noise), it would be more realistic to simulate ice shelf calving with autocorrelation in time. This would lead to greater stochastic glacier variability (Mantelli et al, ; Roe & Baker, ) and perhaps an even larger shift in the time‐averaged glacier state.…”

Section: Nonlinearity Of Noisy Processes Causes Grounding Line Retreatmentioning

confidence: 99%

Response of Marine‐Terminating Glaciers to Forcing: Time Scales, Sensitivities, Instabilities, and Stochastic Dynamics

2018

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Recent observations indicate that many marine-terminating glaciers in Greenland and Antarctica are currently retreating and thinning, potentially due to long-term trends in climate forcing. In this study, we describe a simple two-stage model that accurately emulates the response to external forcing of marine-terminating glaciers simulated in a spatially extended model. The simplicity of the model permits derivation of analytical expressions describing the marine-terminating glacier response to forcing. We find that there are two time scales that characterize the stable glacier response to external forcing, a fast time scale of decades to centuries, and a slow time scale of millennia. These two time scales become unstable at different thresholds of bed slope, indicating that there are distinct slow and fast forms of the marine ice sheet instability. We derive simple expressions for the approximate magnitude and transient evolution of the stable glacier response to external forcing, which depend on the equilibrium glacier state and the strength of nonlinearity in forcing processes. The slow response rate of marine-terminating glaciers indicates that current changes at some glaciers are set to continue and accelerate in coming centuries in response to past climate forcing and that the current extent of change at these glaciers is likely a small fraction of the future committed change caused by past climate forcing. Finally, we find that changing the amplitude of natural fluctuations in some nonlinear forcing processes, such as ice shelf calving, changes the equilibrium glacier state. Plain Language SummaryWe develop a very simple mathematical model to explain how change in climate causes change in marine glaciers. The model shows that this response mostly occurs in two phases, a fast phase over tens to hundreds of years, and a slow phase over thousands of years. Glaciers have a larger response when they are on flat bedrock or when changes in the length of their ice shelf occur due to iceberg detachment. Even though some glaciers have not thinned or retreated significantly in recent years because they sit on steep downward sloping bedrock, they may experience rapid thinning and retreat in the future as they continue to respond to past climate change over thousands of years. Noise in climate and other processes that cause glaciers to be noisy can potentially cause permanent changes in glacier size.These results indicate that we should include noise when making predictions of glaciers changes so that we can calculate uncertainty in future projections and the impact of noise on permanent glacier size.It has long been understood that glaciers act as integrators of external forcing (Nye, 1960(Nye, , 1963a(Nye, , 1963b(Nye, , 1965. Stochastic noise in climate forcing is integrated by glaciers on a characteristic time scale set by glacier

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“…1d,f). Therefore, although power-law behavior can be used to derive expected return times for extreme events (e.g., Roe and Baker 2016;Ault et al 2013b), the apparent negative scaling in the tropics should not be used to calculate return times for extreme events owing to the lack of negative power-law scaling behavior in this region. We refer to a given time series as ''white'' if it roughly had equal variance at all frequencies and had a flat slope (between 20.2 and 0.2) (Ault et al 2013b) in log-log space, such as precipitation over the North Atlantic in CESM (Fig.…”

Section: B Power Spectra Estimationmentioning

confidence: 99%

Temperature and Precipitation Variance in CMIP5 Simulations and Paleoclimate Records of the Last Millennium

et al. 2017

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Accurate assessments of future climate impacts require realistic simulation of interannual-century-scale temperature and precipitation variability. Here, well-constrained paleoclimate data and the latest generation of Earth system model data are used to evaluate the magnitude and spatial consistency of climate variance distributions across interannual to centennial frequencies. It is found that temperature variance generally increases with time scale in patterns that are spatially consistent among models, especially over the mid-and high-latitude oceans. However, precipitation is similar to white noise across much of the globe. When Earth system model variance is compared to variance generated by simple autocorrelation, it is found that tropical temperature variability in Earth system models is difficult to distinguish from variability generated by simple autocorrelation. By contrast, both forced and unforced Earth system models produce variability distinct from a simple autoregressive process over most high-latitude oceans. This new analysis of tropical paleoclimate records suggests that low-frequency variance dominates the temperature spectrum across the tropical Pacific and Indian Oceans, but in many Earth system models, interannual variance dominates the simulated central and eastern tropical Pacific temperature spectrum, regardless of forcing. Tropical Pacific model spectra are compared to spectra from the instrumental record, but the short instrumental record likely cannot provide accurate multidecadal-centennial-scale variance estimates. In the coming decades, both forced and natural patterns of decade-century-scale variability will determine climaterelated risks. Underestimating low-frequency temperature and precipitation variability may significantly alter our understanding of the projections of these climate impacts.

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The response of glaciers to climatic persistence

Cited by 20 publications

References 53 publications

The contrasting response of outlet glaciers to interior and ocean forcing

The contrasting response of outlet glaciers to interior and ocean forcing

Response of Marine‐Terminating Glaciers to Forcing: Time Scales, Sensitivities, Instabilities, and Stochastic Dynamics

Temperature and Precipitation Variance in CMIP5 Simulations and Paleoclimate Records of the Last Millennium

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