Martin Vermeer

Global sea level linked to global temperature.

We propose a simple relationship linking global sea-level variations on time scales of decades to centuries to global mean temperature. This relationship is tested on synthetic data from a global climate model for the past millennium and the next century. When applied to observed data of sea level and temperature for 1880–2000, and taking into account known anthropogenic hydrologic contributions to sea level, the correlation is >0.99, explaining 98% of the variance. For future global temperature scenarios of the Intergovernmental Panel on Climate Changes Fourth Assessment Report, the relationship projects a sea-level rise ranging from 75 to 190 cm for the period 1990–2100.

Climate related sea-level variations over the past two millennia

We present new sea-level reconstructions for the past 2100 y based on salt-marsh sedimentary sequences from the US Atlantic coast. The data from North Carolina reveal four phases of persistent sea-level change after correction for glacial isostatic adjustment. Sea level was stable from at least BC 100 until AD 950. Sea level then increased for 400 y at a rate of 0.6 mm/y, followed by a further period of stable, or slightly falling, sea level that persisted until the late 19th century. Since then, sea level has risen at an average rate of 2.1 mm/y, representing the steepest century-scale increase of the past two millennia. This rate was initiated between AD 1865 and 1892. Using an extended semiempirical modeling approach, we show that these sea-level changes are consistent with global temperature for at least the past millennium.

Testing the robustness of semi-empirical sea level projections

We determine the parameters of the semi-empirical link between global temperature and global sea level in a wide variety of ways, using different equations, different data sets for temperature and sea level as well as different statistical techniques. We then compare projections of all these different model versions (over 30) for a moderate global warming scenario for the period 2000–2100. We find the projections are robust and are mostly within ±20% of that obtained with the method of Vermeer and Rahmstorf (Proc Natl Acad Sci USA 106:21527–21532, 2009), namely ~1 m for the given warming of 1.8°C. Lower projections are obtained only if the correction for reservoir storage is ignored and/or the sea level data set of Church and White (Surv Geophys, 2011) is used. However, the latter provides an estimate of the base temperature T0 that conflicts with the constraints from three other data sets, in particular with proxy data showing stable sea level over the period 1400–1800. Our new best-estimate model, accounting also for groundwater pumping, is very close to the model of Vermeer and Rahmstorf (Proc Natl Acad Sci USA 106:21527–21532, 2009).

Predictability of twentieth century sea-level rise from past data

The prediction of global sea-level rise is one of the major challenges of climate science. While process-based models are still being improved to capture the complexity of the processes involved, semi-empirical models, exploiting the observed connection between global-mean sea level and global temperature and calibrated with data, have been developed as a complementary approach. Here we investigate whether twentieth century sea-level rise could have been predicted with such models given a knowledge of twentieth century global temperature increase. We find that either proxy or early tide gauge data do not hold enough information to constrain the model parameters well. However, in combination, the use of proxy and tide gauge sea-level data up to 1900 AD allows a good prediction of twentieth century sea-level rise, despite this rise being well outside the rates experienced in previous centuries during the calibration period of the model. The 90% confidence range for the linear twentieth century rise predicted by the semi-empirical model is 13‐30 cm, whereas the observed interval (using two tide gauge data sets) is 14‐26 cm.

Discussion of: Houston, J.R. and Dean, R.G., 2011. Sea-Level Acceleration Based on U.S. Tide Gauges and Extensions of Previous Global-Gauge Analyses. Journal of Coastal Research, 27(3), 409–417

Abstract A recent article published in the Journal of Coastal Research analysed a number of different sea-level records and reported that they found no acceleration of sea-level rise. We show that this is due to their focusing on records that are either too short or only regional in character, and on their specific focus on acceleration since the year 1930, which represents a unique minimum in the acceleration curve. We find that global sea-level rise is accelerating in a way strongly correlated with global temperature. This correlation also explains the acceleration minimum for time periods starting around 1930; it is due to the mid-twentieth-century plateau in global temperature.

Long-term sea-level rise implied by 1.5 degrees C and 2 degrees C warming levels

Sea-level rise is one of the key consequences of climate change. Its impact is long-term owing to the multi-century response timescales involved. This study addresses how much sea-level rise will result in coming centuries from climate-policy decisions taken today.

Modelling land uplift rates and their error propagation

Abstract The article describes a method for deriving the precision of a predicted land uplift value at an arbitrary terrain point which is assumed connected in height to a levelling benchmark using GNSS and a precise geoid model. We derive a statistical model for predicting the uplift rate from the existing point rates along with its empirical signal covariance function. One of our aims is a study on how a land uplift rate model and its empirical covariance function can be determined and then used for calculating changes in height over the time interval between precise levellings or GNSS heightings.