Aslak Grinsted

University of Copenhagen · Center for Ice and Climate

The Greenland Ice Sheet has become an increasingly larger contributor to sea level rise in the past two decades and is projected to continue to lose mass. Climate variability is expected to increase under future warming, but the effect of climate variability on the Greenland Ice Sheet volume is poorly understood and is adding to the uncertainty of...

Subglacial hydrology can exert an important control on ice flow by affecting friction at the ice‐bedrock interface. Here, we report on a series of subglacial drainage events along the Northeast Greenland Ice Stream (NEGIS), initiating as far inland as 500 km from the margin of Zachariae Isstrøm. The drainage events exhibit local transient uplift, f...

The dynamic mass loss of ice sheets constitutes one of the biggest uncertainties in projections of ice-sheet evolution. One central, understudied aspect of ice flow is how the bulk orientation of the crystal orientation fabric translates to the mechanical anisotropy of ice. Here we show the spatial distribution of the depth-averaged horizontal anis...

Subglacial hydrology can exert an important control on ice flow by affecting drag at the ice-bedrock interface. Here, we report on a series of subglacial drainage events (outbursts) along the Northeast Greenland Ice Stream (NEGIS), initiating as far inland as ~500 km from the margin of Zachariae Isstrøm. The drainage events are associated with loca...

An optimization problem is proposed for inferring physical properties of polycrystals given ultrasonic (elastic) wave velocity measurements, made across multiple sample orientations. The feasibility of the method is demonstrated by inferring both the effective grain elastic parameters and the grain c -axis orientation distribution function (ODF) of...

Earth is warming and sea levels are rising as land‐based ice is lost to melt, and oceans expand due to accumulation of heat. The pace of ice loss and steric expansion is linked to the intensity of warming. How much faster sea level will rise as climate warms is, however, highly uncertain and difficult to model. Here, we quantify the transient sea l...

Mass loss near the ice-sheet margin is evident from remote sensing as frontal retreat and increases in ice velocities. Velocities in the ice sheet interior are orders of magnitude smaller, making it challenging to detect velocity change. Here, we analyze a 35-year record of remotely sensed velocities, and a 6-year record of repeated GPS observation...

In the accumulation zone of glaciers and ice sheets snow is transformed into glacial ice by firn densification. Classically, this process is assumed to solely depend on temperature and overburden pressure, which is controlled by the accumulation rate. However, exceptionally thin firn layers have been observed in the high-strain shear margins of ice...

The dynamic mass loss of ice sheets due to ice flow constitutes one of the biggest uncertainties in projections of ice-sheet evolution and sea-level rise. One central, understudied aspect of ice flow is how the bulk orientation of the ice-crystal lattice (fabric) translates to the mechanical anisotropy of ice. Here, we present a comprehensive analy...

The Müller Ice Cap will soon set the scene for a new drilling project. Therefore, ice thickness estimates are necessary for planning, since thickness measurements of the ice cap are sparse. Here, three models are presented and compared: (i) a simple Semi-Empirical Ice Thickness Model (SEITMo) based on an inversion of the shallow-ice approximation b...

Plain Language Summary The orientation of ice crystals in glacier ice locally co‐evolve with and can enhance the flow of ice. Methods that allow inferring the crystal structure inside glaciers and ice sheets are, therefore, essential for improving the accuracy and realism of ice‐flow models, and have broad implications for understanding past and pr...

In the accumulation zone of glaciers and ice sheets snow is transformed into glacial ice by firn densification. Classically, this processes is assumed to solely depend on temperature and overburden pressure which is controlled by the accumulation rate. However, exceptionally thin firn layers have been observed in the high-strain shear margins of ic...

The Müller Ice Cap will soon set the scene for a new drilling project. Therefore, ice thickness estimates are necessary for planning since thickness measurements of the ice cap are sparse. Here, two models are presented and compared, i) a simple inversion of the shallow ice approximation (SIA inversion) by the use of a single radar line in combinat...

Please cite the corresponding article of the Supplement when using this data. ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ Description: 1) The spread sheet 'GICC05-EGRIP-1_10Jun2021.xls' contai...

The Northeast Greenland Ice Stream (NEGIS) is the largest active ice stream on the Greenland Ice Sheet (GrIS) and a crucial contributor to the ice-sheet mass balance. To investigate the ice-stream dynamics and to gain information about the past climate, a deep ice core is drilled in the upstream part of the NEGIS, termed the East Greenland Ice-core...

Data availability and temporal resolution make it challenging to unravel the anatomy (duration and temporal phasing) of the Last Glacial abrupt climate changes. Here, we address these limitations by investigating the anatomy of abrupt changes using sub-decadal-scale records from Greenland ice cores. We highlight the absence of a systematic pattern...

To assess the amount of ice volume stored in glaciers or ice caps, a method to estimate ice thickness distribution is required for glaciers where no direct observations are available. In this study, we use an existing inverse method to estimate the bedrock topography and ice thickness of the Renland Ice Cap, East Greenland, using satellite-based ob...

The Northeast Greenland Ice Stream (NEGIS) is the largest active ice stream on the Greenland Ice Sheet (GrIS) and a crucial contributor to the ice-sheet mass balance. To investigate the ice-stream dynamics and to gain information about the past climate, a deep ice core is drilled in the upstream part of the NEGIS, termed the East Greenland Ice-Core...

Recent assessments from the Intergovernmental Panel on Climate Change (IPCC) imply that global mean sea level is unlikely to rise more than about 1.1 m within this century but will increase further beyond 2100. Even within the most intensive future anthropogenic greenhouse gas emission scenarios, higher levels are assessed to be unlikely. However,...

Bulk directional enhancement factors are determined for axisymmetric (girdle and single-maximum) orientation fabrics using a transversely isotropic grain rheology with an orientation-dependent non-linear grain fluidity. Compared to grain fluidities that are simplified as orientation independent, we find that bulk strain-rate enhancements for interm...

The Northeast Greenland Ice Stream (NEGIS) extends around 600 km upstream from the coast to its onset near the ice divide in interior Greenland. Several maps of surface velocity and topography of interior Greenland exist, but their accuracy is not well constrained by in situ observations. Here we present the results from a GPS mapping of surface ve...

Recent assessments from the Intergovernmental Panel on Climate Change implies that global mean sea level is unlikely to rise more than about 1.1 m within this century, but with further increase beyond 2100, even within the most intensive future anthropogenic carbon dioxide emission scenarios. However, some studies conclude that considerably greater...

In recent years, the Sentinel-1 satellites have provided a data archive of unprecedented volume, delivering C-band Synthetic Aperture Radar (SAR) acquisitions over most of the polar ice sheets with a repeat-pass period of 6-12 days using Interferometric Wide swath (IW) imagery acquired in Terrain Observation by Progressive Scans (TOPS) mode. Due to...

Abstract. The Northeast Greenland Ice Stream (NEGIS) extends around 600 km upstream from the coast to its onset near the ice divide in interior Greenland. Several maps of surface velocity and topography in the interior Greenland exist, but the accuracy is not well constrained by in situ observations and limiting detailed studies of flow structures...

We use remotely sensed ice velocities in combination with observations of surface elevation and glacier area change to investigate the dynamics of Hagen Bræ, North Greenland in high detail over the last 35 years. From our data, we can establish for the first time that Hagen Bræ is a surge-type glacier with characteristics of both Alaskan- and Svalb...

Significance We present an approach to normalize hurricane damage, where damage is framed in terms of an equivalent area of total destruction. This has some advantages over customary normalization schemes, and we demonstrate that our record has reduced variance and correlates marginally better with wind speeds and pressure. That is, it allows us to...

Accurate estimates of the past extent of the Greenland ice sheet provide critical constraints for ice sheet models used to determine Greenland’s response to climate forcing and contribution to global sea level. Here we use a continuous ice core dust record from the Renland ice cap on the east coast of Greenland to constrain the timing of changes to...

We estimate a median global sea level rise up to 52 cm (25–87 cm, 5th–95th percentile) and up to 63 cm (27−112 cm, 5th—95th percentile) for a temperature rise of 1.5 °C and 2.0 °C by 2100 respectively. We also estimate global annual flood costs under these scenarios and find the difference of 11 cm global sea level rise in 2100 could result in addi...

Engabreen is an outlet glacier of the Svartisen Ice Cap located in Northern Norway. It is a unique glacier due to the Svartisen Subglacial Laboratory which allows direct access to the glacier bed. In this study, we combine both sub- and supraglacial observations with ice-flow modelling in order to investigate conditions at the bed of Engabreen both...

As global average sea‐level rises in the early part of this century there is great interest in how much global and local sea level will change in the forthcoming decades. The Paris Climate Agreement's proposed temperature thresholds of 1.5°C and 2°C have directed the research community to ask what differences occur in the climate system for these t...

Forecasting the future sea level relies on accurate modeling of the response of the Greenland and Antarctic ice sheets to changing temperatures. The surface mass balance (SMB) of the Greenland Ice Sheet (GrIS) has a nonlinear response to warming. Cold and warm anomalies of equal size do not cancel out and it is therefore important to consider the e...

We report evidence of four cycles of outburst floods from Catalina Lake, an ice-dammed lake in East Greenland, identified in satellite imagery between 1966-2016. The lake measures 20-25 km², and lake level drops 130-150 m in each event, corresponding to a water volume of 2.6-3.4 Gt, and a release of potential energy of 10¹⁶ J, among the largest out...

The seasonal response to surface melting of the Northeast Greenland Ice Stream outlets, Zachariae and 79N, is investigated using new highly temporally resolved surface velocity maps for 2016 combined with numerical modelling. The seasonal speed-up at 79N of 0.15km/yr is suggested to be driven by a decrease in effective basal pressure induced by sur...

Forecasting the future sea level relies on accurate modeling of the response of the Greenland and Antarctic ice sheets to changing temperatures. We show why the steady state of an ice sheet is biased toward larger size if the interannual weather generated fluctuations in temperature are not taken into account in numerical modeling of the ice sheet....

Significance Warming of 2 °C will lead to an average global ocean rise of 20 cm, but more than 90% of coastal areas will experience greater rises. If warming continues above 2 °C, then, by 2100, sea level will be rising faster than at any time during human civilization, and 80% of the global coastline is expected to exceed the 95th percentile upper...

Significance We estimate that stratospheric sulfate aerosol geoengineering may somewhat ameliorate Atlantic hurricane intensity and frequency, but there will be more “Katrina”-level events than during the past 30 y. Geoengineering would likely be reasonably effective at controlling coastal flood risk relative to the coastal flood risk expected unde...

Sea level rise poses a significant threat to coastal communities, infrastructure, and ecosystems. Sea level rise is not uniform globally but is affected by a range of regional factors. In this study, we calculate regional projections of 21st century sea level rise in northern Europe, focusing on the British Isles, the Baltic Sea, and the North Sea....

Global warming is causing sea levels to rise, primarily due to loss of land-based ice masses and thermal (steric) expansion of the world oceans. Sea level does not rise in a globally uniform manner, but varies in complex spatial patterns. This chapter reviews projections of the individual contributions to sea-level rise. These are used to assemble...

The use of time-lapse camera systems is becoming an increasingly popular method for data acquisition. The camera setup is often cost-effective and simple, allowing for a large amount of data to be accumulated over a variety of environments for relatively minimal effort. The acquired data can, with the correct post-processing, result in a wide range...

This study presents average velocity fields, mass flux estimates and central flowline profiles for five major Greenland outlet glaciers; Jakobshavn Isbræ, Nioghalvfjerdsbræ, Kangerdlugssuaq, Helheim and Petermann glaciers, spanning the period (August) 2013–(September) 2014. The results are produced by the feature tracking toolbox, ImGRAFT using Lan...

We construct the probability density function of global sea level at 2100, estimating that sea level rises larger than 180 cm are less than 5% probable. An upper limit for global sea level rise of 190 cm is assembled by summing the highest estimates of individual sea level rise components simulated by process based models with the RCP8.5 scenario....

The use of time-lapse camera systems is becoming an increasingly popular method for data acquisition. The camera setup is often cost-effective and simple, allowing for a large amount of data to be accumulated over a variety of environments for relatively minimal effort. The acquired data can, with the correct post-processing, result in a wide range...

In order to extract the intrinsic information of climatic time series from background red noise, in this paper, we will first give an analytic formula on the distribution of Haar wavelet power spectra of red noise in a rigorous statistical framework. After that, by comparing the difference of wavelet power spectra of real climatic time series and r...

[1] We review the two main approaches to estimating sea level rise over the coming century: physically plausible models of reduced complexity that exploit statistical relationships between sea level and climate forcing, and more complex physics-based models of the separate elements of the sea level budget. Previously, estimates of future sea level...

We appreciate the opportunity to discuss our definition of events of Katrina magnitude. Kennedy et al. (1) argue that our definition of Katrina magnitude events (2) is too low because we do not use any tide gauge data in the immediate proximity of New Orleans and the region of absolute maximal surge height.

We use 1277 tide gauge records since 1807 to compose a global sea level reconstruction and analyse the evolution of sea level trend and acceleration. There is a good agreement between the rate of sea level rise (3.2 mm/yr) calculated from satellite altimetry and the rate of 3.1 mm/yr from tide gauge based reconstruction for the overlapping time per...

I will show empirical evidence for how global warming has changed extreme storm surge statistics for different regions in the world. Are there any detectable changes beyond what we expect from sea level rise. What does this suggest about the future of hurricane surges such as from hurricane Katrina and superstorm Sandy?

I asses the feasibility of using multi-variate scaling relationships to estimate glacier volume from glacier inventory data. Scaling laws are calibrated against volume observations optimized for the specific purpose of estimating total global glacier ice volume. I find that adjustments for continentality and elevation range improve skill of area-vo...

We review the two main approaches to estimating sea level rise over the coming century: physically plausible models of reduced complexity that exploit statistical relationships between sea level to climate forcing, and more complex physics-based models of the separate elements of the sea level budget. Recent estimates of sea level rise by 2100 have...

Different strategies can be chosen to initialize an ice-sheet model to a state representing present-day conditions. Here we use a forward approach where the ice-sheet model is forced with a paleo-climatic history and allowed to evolve to its present-day state. Nine model parameters are varied in order to form a large ensemble of possible solutions...

Detection and attribution of past changes in cyclone activity are hampered by biased cyclone records due to changes in observational capabilities. Here, we relate a homogeneous record of Atlantic tropical cyclone activity based on storm surge statistics from tide gauges to changes in global temperature patterns. We examine 10 competing hypotheses u...

Efforts to extract a Greenland ice core with a complete record of the Eemian interglacial (130,000 to 115,000 years ago) have until now been unsuccessful. The response of the Greenland ice sheet to the warmer-than-present climate of the Eemian has thus remained unclear. Here we present the new North Greenland Eemian Ice Drilling (‘NEEM’) ice core a...

We use 1277 tide gauge records since 1807 to provide an improved global sea level reconstruction and analyse the evolution of sea level trend and acceleration. In particular we use new data from the polar regions and remote islands to improve data coverage and extend the reconstruction to 2009. There is a good agreement between the rate of sea leve...

Detection and attribution of past changes in cyclone activity are hampered by biased cyclone records due to changes in observational capabilities. Here we construct an independent record of Atlantic tropical cyclone activity on the basis of storm surge statistics from tide gauges. We demonstrate that the major events in our surge index record can b...

We examine the limitations of a semiempirical model characterized by a sea level projection of 73 cm with RCP4.5 scenario by 2100. Calibrating the model with data to 1990 and then simulating the period 1993-2009 produces sea level in close agreement with acceleration in sea level rise observed by satellite altimetry. Nonradiative forcing contributo...

I asses the feasibility of multi-variate scaling relationships to estimate glacier volume from glacier inventory data. I calibrate scaling laws against volume observations of optimized towards the purpose of estimating the total global ice volume. This is applied individually to each record in the Randolph Glacier Inventory which is the first globa...

Four new Representative Concentration Pathways radiative forcing scenarios are used to estimate sea level rise of 0.57-1.10 m by 2100 with semi-empirical model. In this study, a semi-empirical model is constrained by the 300 years of global sea level records from tide gauges and driven by various radiative forcing time series (solar, volcanic, gree...

We use all available tide gauge records since 1807 to compose a global sea level reconstruction and analyse the evolution of global and regional sea level trends and their acceleration. Regional linear trends for 14 ocean basins since 1960 suggest the fastest sea level rise near the coast of Antarctica (3.6 mm/yr) and North West Pacific region (3.4...

Sea level rise over the coming centuries is perhaps the most damaging side of rising temperature (Anthoff et al., 2009). The economic costs and social consequences of coastal flooding and forced migration will probably be one of the dominant impacts of global warming (Sugiyama et al., 2008). To date, however, few studies (Nicholls et al., 2008; Ant...

We analyze the global sea-level budget since 1850. Good estimates of sea-level contributions from glaciers and small ice caps, the Greenland ice sheet and thermosteric sea level are available over this period, though considerable scope for controversy remains in all. Attempting to close the sea-level budget by adding the components results in a res...

We use all available tide gauge records since 1807 to compose global and regional sea level reconstructions and analyse the evolution of sea level trends and changes in low/high frequency variability. Decadal sea level trends for 14 ocean basins show a lot of variability and divergent regional patterns; for example, strong rise since 1990s in Centr...

Kemp et al. (1) presented a new salt-marsh proxy record of relative sea level (RSL) from North Carolina (NCRSL). The salt marsh is slowly subsiding as a result of glacial isostatic adjustment (GIA), and the NCRSL record needs to be adjusted to remove this vertical land movement from the sea level record. Kemp et al. (1) corrected for a constant sub...

Sea level rise is perhaps the most damaging repercussion of global warming, as 150 million people live less than one meter above current high tides .Using an inverse statistical model we examine potential response in coastal sea level to the changes in natural and anthropogenic forcings by 2100. With six IPCC radiative forcing scenarios we estimate...

Geoengineering has been proposed as a feasible way of mitigating anthropogenic climate change, especially increasing global temperatures in the 21st century. The two main geoengineering options are limiting incoming solar radiation, or modifying the carbon cycle. Here we examine the impact of five geoengineering approaches on sea level; SO(2) aeros...

We used tide gauge records to construct an index of storm surge intensity in the tropical Atlantic cyclone region, which we interpret as a measure of the threat posed by tropical cyclones. Changes in surge index return periods are related to changes in global average temperature at the 95% significance level. Surge risk increases with temperature f...

Geoengineering has been proposed as a feasible way of mitigating anthropogenic climate change, especially increasing global temperatures in the 21st century. The two main geoengineering options are limiting incoming solar radiation, or modifying the carbon cycle. Here we examine the impact of 5 geoengineering approaches on sea level; SO2 aerosol in...

Geophysical studies are plagued by short and noisy time series. These time series are typically nonstationary, contain various quasi-periodic components, and have rather low signal-to-noise ratios and poor spatial sampling. Classic examples of these time series are tide gauge records. We employ a delayed response statistical model to relate the pas...

We examine the links between the 11 year solar cycle and ocean variability. We analyze 3 independent data sets: global sea level, sea surface temperature, and ocean heat content using a variety of statistical methods and noise backgrounds. The choice of noise background (white or red noise, bootstrapping, and Fourier transformed) in testing quasi-m...

Semi-empirical models for global sea level rise currently provide the best guess for projections of sea level. Here, a statistical comparison of recent semi-empirical models for global sea level rise will be presented.

We discuss a novel wavelet-lag coherence method to study of cause-and-effect relations over a large space of timescales, phase lags and periods. We use 135 years of observational records to demonstrate how sea-surface temperature, sea-level pressure and cyclone numbers are linked. We examine the statistical properties of the time series and test ho...

The rate of sea level rise and its causes are topics of active debate. Here we use a delayed response statistical model to attribute the past 1000 years of sea level variability to various natural (volcanic and solar radiative) and anthropogenic (greenhouse gases and aerosols) forcings. We show that until 1800 the main drivers of sea level change a...

We reconstructed decadal to centennial variability of maximum sea ice extent in the Western Nordic Seas for A.D. 1200–1997 using a combination of a regional tree-ring chronology from the timberline area in Fennoscandia and δ18O from the Lomonosovfonna ice core in Svalbard. The reconstruction successfully explained 59% of the variance in sea ice ext...

We examine the relationship between 50 year long records of global sea level (GSL) calculated from 1023 tide gauge stations and global ocean heat content (GOHC), glacier and ice sheet melting. The sea level contributions calculated from continental glacier volume changes and ice sheet melting in Greenland and Antarctica make up the leading componen...