Glacier fluctuations, global temperature and sea-level change

The current world-wide glacier retreat is a clear sign of global warming. In addition, glaciers contribute to sea-level rise as a consequence of the current retreat. In this thesis we use records of past glacier fluctuations to reconstruct past climate variations and the glacier contribution to sea-level change. Firstly, a coherent data set of world-wide glacier fluctuations over the past centuries is compiled. Most available information of glacier fluctuations concerns glacier length fluctuations. There is currently a large number of sources available, varying from field observations, satellite images and aerial photography to reconstructions from historical documents and geological evidence. The data set, resulting from the compilation of available data, contains 374 length records of glaciers from all continents and is described in Chapter 2. In Chapter 3, a climatic interpretation of the length fluctuations of Glaciar Frías is presented. This glacier in North Patagonia has the longest detailed length record in southern South America. The glacier behaviour is modelled with a simplified mass balance model that is coupled with a flow line model. A warming of North Patagonian climate with 1.16 °Csince the mid 17th century, or a decrease in precipitation of 34%, would best explain the observed retreat since 1639. Driving the glacier model with existing climate reconstructions shows that the uncertainties in these reconstructions are rather large. In addition, it appears that the length fluctuations are mainly driven by variations in temperature rather than variations in precipitation. The development of such detailed models is not feasible for all glaciers in the length fluctuations data set. In the next chapter a simplified approach is used to reconstruct global and hemispheric temperature for the period 1600–2000 from world-wide glacier length fluctuations. The reconstructions show that global temperature was more or less constant from 1600 until the middle of the 19th century. Since then, temperature rises until 2000, with a period of slight cooling from 1940 to 1970. Glacier-based reconstructions are completely independent from both other proxy-based reconstructions and from the instrumental record. Still, the reconstructed temperature agrees well with the instrumental record of the 20th century and it is in broad agreement with existing temperature reconstructions. However, according to the glacier length reconstruction the global warming starts in the middle of the 19th century instead of in the beginning of the 20th century, as indicated by several other reconstructions. The data set of glacier length changes can also be used to estimate the glacier contribution to sea-level change. In Chapter 5, a global glacier length signal is calculated from the available glacier length records. The global length signal is scaled to global volume change, which is calibrated on mass balance and geodetic observations of the period 1950–2005. The reconstructed glacier contribution is 8.4 ± 2.1 cm for the period 1800–2005 and 9.1 ± 2.3 cm for the period 1850–2005. These estimates are significantly higher than earlier estimates. Glacier retreat accounts for half the observed sea-level rise since the middle of the 19th century

Global and hemispheric temperature reconstruction from glacier length fluctuations

A library of more than 4,500 signature-tagged insertion mutants of the human pathogenic fungus Cryptococcus neoformans was generated, and a subset was screened in a murine inhalation model to identify genes required for virulence. New genes that regulate aspects of C. neoformans virulence were also identified by screening the entire library for in vitro phenotypes related to the ability to cause disease, including melanin production, growth at high temperature, and growth under conditions of nutrient limitation. A screen of 10% of the strain collection in mice identified an avirulent mutant strain with an insertion in the ENA1 gene, which is predicted to encode a fungus-specific sodium or potassium P-type ATPase. The results of the deletion of the gene and complementation experiments confirmed its key role in mammalian virulence. ena1 mutant strains exhibited no change in sensitivity to high salt concentrations but were sensitive to alkaline pH conditions, providing evidence that the fungus may have to survive at elevated pH during infection of the mammalian host. The mutation of the well-characterized virulence factor calcineurin (CNA1) also rendered C. neoformans strains sensitive to elevated pH. ENA1 transcripts in wild-type and cna1 mutant strains were upregulated in response to high pH, and cna1 ena1 double mutant strains exhibited increased sensitivity to elevated pH, indicating that at least two pathways in the fungus mediate survival under alkaline conditions. Signature-tagged mutagenesis is an effective strategy for the discovery of new virulence genes in fungal pathogens of animals

Estimating the glacier contribution to sea-level rise for the period 1800-2005

In this study, a new estimate of the contribution of glaciers and ice caps to the sea-level rise over the period 1800-2005 is presented. We exploit the available information on changes in glacier length. Length records form the only direct evidence of glacier change that has potential global coverage before 1950. We calculate a globally representative signal from 349 glacier length records. By means of scaling, we deduce a global glacier volume signal, that is calibrated on the mass-balance and geodetic observations of the period 1950-2005. We find that the glacier contribution to sea-level rise was 8.4 ± 2.1 cm for the period 1800-2005 and 9.1 ± 2.3 cm for the period 1850-2005

Glacier fluctuations, global temperature and sea-level change

The current world-wide glacier retreat is a clear sign of global warming. In addition, glaciers contribute to sea-level rise as a consequence of the current retreat. In this thesis we use records of past glacier fluctuations to reconstruct past climate variations and the glacier contribution to sea-level change. Firstly, a coherent data set of world-wide glacier fluctuations over the past centuries is compiled. Most available information of glacier fluctuations concerns glacier length fluctuations. There is currently a large number of sources available, varying from field observations, satellite images and aerial photography to reconstructions from historical documents and geological evidence. The data set, resulting from the compilation of available data, contains 374 length records of glaciers from all continents and is described in Chapter 2. In Chapter 3, a climatic interpretation of the length fluctuations of Glaciar Frías is presented. This glacier in North Patagonia has the longest detailed length record in southern South America. The glacier behaviour is modelled with a simplified mass balance model that is coupled with a flow line model. A warming of North Patagonian climate with 1.16 °Csince the mid 17th century, or a decrease in precipitation of 34%, would best explain the observed retreat since 1639. Driving the glacier model with existing climate reconstructions shows that the uncertainties in these reconstructions are rather large. In addition, it appears that the length fluctuations are mainly driven by variations in temperature rather than variations in precipitation. The development of such detailed models is not feasible for all glaciers in the length fluctuations data set. In the next chapter a simplified approach is used to reconstruct global and hemispheric temperature for the period 1600–2000 from world-wide glacier length fluctuations. The reconstructions show that global temperature was more or less constant from 1600 until the middle of the 19th century. Since then, temperature rises until 2000, with a period of slight cooling from 1940 to 1970. Glacier-based reconstructions are completely independent from both other proxy-based reconstructions and from the instrumental record. Still, the reconstructed temperature agrees well with the instrumental record of the 20th century and it is in broad agreement with existing temperature reconstructions. However, according to the glacier length reconstruction the global warming starts in the middle of the 19th century instead of in the beginning of the 20th century, as indicated by several other reconstructions. The data set of glacier length changes can also be used to estimate the glacier contribution to sea-level change. In Chapter 5, a global glacier length signal is calculated from the available glacier length records. The global length signal is scaled to global volume change, which is calibrated on mass balance and geodetic observations of the period 1950–2005. The reconstructed glacier contribution is 8.4 ± 2.1 cm for the period 1800–2005 and 9.1 ± 2.3 cm for the period 1850–2005. These estimates are significantly higher than earlier estimates. Glacier retreat accounts for half the observed sea-level rise since the middle of the 19th century

Modelling and climatic interpretation of the length fluctuations of glaciar Frías (North Patagonia, Argentina) 1639-2009 AD

We explore the climatic information contained in the record of length fluctuations of Glaciar Frías, in the north Patagonian Andes of Argentina. This record is one of the longest and most detailed glacier records in southern South America, starting in 1639. In order to interpret the length variations of Glaciar Frías since the maximum Little Ice Age extent, we use a combination of a simplified surface energy-balance model to calculate the glacier mass balance, and a flowline model to account for the dynamical response of the glacier to changes in the climatic forcing. The overall retreat of the glacier observed over 1639–2009 is best explained by an annual mean temperature increase of 1.2 °C or a decrease in annual precipitation of 34%, most of which would have occurred during the 20th century. The glacier model is also forced with two independent tree-ring and multi-proxy reconstructions of precipitation and temperature. The uncertainties in these reconstructions are rather large, leading to a wide range in the modelled glacier length that includes most of the observations. However, in both reconstructions, the mid-17th century seems to be too cold and the early 19th century too warm to explain the observed glacier lengths with the glacier model forced with the reconstructions. Forcing with reconstructed precipitation and temperature separately shows that the influence of historical variations in precipitation on the glacier fluctuations of Glaciar Frías is smaller than that of the temperature fluctuations. This suggests that the observed 1639–2009 retreat could be best explained by a warming close to 1.2 °C

A data set of worldwide glacier fluctuations

Glacier fluctuations contribute to variations in sea level and historical glacier length fluctuations are natural indicators of past climate change. To study these subjects, longterm information of glacier change is needed. In this paper we present a data set of global long-term glacier length fluctuations. The data set is a compilation of available information on changes in glacier length worldwide, including both measured and reconstructed glacier length fluctuations. All 471 length series start before 1950 and cover at least four decades. The longest record starts in 1535, but the majority of time series start after 1850. The number of available records decreases again after 1962. The data set has global coverage including records from all continents. However, the Canadian Arctic is not represented in the data set. The available glacier length series show relatively small fluctuations until the mid-19th century, followed by a global retreat. The retreat was strongest in the first half of the 20th century, although large variability in the length change of the different glaciers is observed. During the 20th century, calving glaciers retreated more than land-terminating glaciers, but their relative length change was approximately equal. Besides calving, the glacier slope is the most important glacier property determining length change: steep glaciers have retreated less than glaciers with a gentle slope

A data set of worldwide glacier length fluctuations

Glacier fluctuations contribute to variations in sea level and historical glacier length fluctuations are natural indicators of past climate change. To study these subjects, long-term information of glacier change is needed. In this paper we present a data set of global long-term glacier length fluctuations. The data set is a compilation of available information on changes in glacier length worldwide, including both measured and reconstructed glacier length fluctuations. All 471 length series start before 1950 and cover at least four decades. The longest record starts in 1535, but the majority of time series start after 1850. The number of available records decreases again after 1962. The data set has global coverage including records from all continents. However, the Canadian Arctic is not represented in the data set. The available glacier length series show relatively small fluctuations until the mid-19th century, followed by a global retreat. The retreat was strongest in the first half of the 20th century, although large variability in the length change of the different glaciers is observed. During the 20th century, calving glaciers retreated more than land-terminating glaciers, but their relative length change was approximately equal. Besides calving, the glacier slope is the most important glacier property determining length change: steep glaciers have retreated less than glaciers with a gentle slope

Brief communication "Historical glacier length changes in West Greenland"

Past glacier fluctuations provide insight into glacier dynamics, climate change, and the contribution of glaciers to sea-level rise. Here, the length fluctuations since the 19th century of 18 local glaciers in West and South Greenland are presented, extending and updating the study by Weidick (1968). The studied glaciers all showed an overall retreat with an average of 1.2 ± 0.2 km over the 20th century, indicating a general rise of the equilibrium line along the west coast of Greenland during the last century. Furthermore, the average rate of retreat was largest in the first half of the 20th century

Twentieth-century global-mean sea-level rise: is the whole greater than the sum of the parts?

Confidence in projections of global-mean sea level rise (GMSLR) depends on an ability to account for GMSLR during the twentieth century. There are contributions from ocean thermal expansion, mass loss from glaciers and ice sheets, groundwater extraction, and reservoir impoundment. Progress has been made toward solving the ‘‘enigma’’ of twentieth-century GMSLR, which is that the observed GMSLR has previously been found to exceed the sum of estimated contributions, especially for the earlier decades. The authors propose the following: thermal expansion simulated by climate models may previously have been underestimated because of their not including volcanic forcing in their control state; the rate of glacier mass loss was larger than previously estimated and was not smaller in the first half than in the second half of the century; the Greenland ice sheet could have made a positive contribution throughout the century; and groundwater depletion and reservoir impoundment, which are of opposite sign, may have been approximately equal in magnitude. It is possible to reconstruct the time series of GMSLR fromthe quantified contributions, apart from a constant residual term, which is small enough to be explained as a long-term contribution from the Antarctic ice sheet. The reconstructions account for the observation that the rate of GMSLR was not much larger during the last 50 years than during the twentieth century as a whole, despite the increasing anthropogenic forcing. Semiempirical methods for projecting GMSLR depend on the existence of a relationship between global climate change and the rate of GMSLR, but the implication of the authors’ closure of the budget is that such a relationship is weak or absent during the twentieth century