The reconstructed Mt. Hunter temperature record (top) compared with instrumental (Lawrimore et al., 2011) and paleoproxy (Clegg et al., 2010; Davi et al., 2003; Hu et al., 2001; Loso, 2009; Wiles et al., 2014) temperature records from low‐elevation sites in southern and central Alaska. The records from Core 1 (pink) and Core 2 (red) both show a pronounced warming. The dashed black line indicates the maximum temperature relative to present during periods with no melt layers. The Mt. Hunter records are shown as 31‐year running means for clarity. All data are shown in °C relative to present with a consistent y scale between each data set. Graphic: Winski, et al., 2018 / Journal of Geophysical Research

By John Abraham
18 April 2018

(The Guardian) – With global warming, we can make predictions and then take measurements to test those predictions. One prediction (a pretty obvious one) is that a warmer world will have less snow and ice. In particular, areas that have year-round ice and snow will start to melt.

Alpine glaciers are large bodies of ice that can be formed high in mountains, typically in bowls called cirques. The ice slowly flows downwards, pulled by gravity, and is renewed in their upper regions. A sort of balance can occur where the loss of ice by melting or flowing at the bottom is equal to the gain of snow and ice by precipitation.

As the Earth warms, the melt line moves upwards so that the glacier melts faster and faster at the bottom, shortening the glacier and reducing its mass. Ultimately, the melted water flows into streams and rivers and ends up in the oceans, contributing to accelerating sea level rise.

While glaciers are interesting from an intellectual standpoint, they are also important to ecosystems and society. For example, the rate of glacier melt affects downstream water levels, river flowrates, and the water available for human use. So, it would be really important for us to be able to predict what will happen with glaciers in the future and plan for how water availability will change.

Of the groups that track glaciers, my favorite is the World Glacier Monitoring Service, which publishes a survey of the mass changes from selected glaciers around the world, available here and summarized below. The graph shows changes to the mass of the glaciers that are monitored, measured in millimeters of equivalent water.

But this doesn’t tell the whole story because there is very little information about glacier health in the high latitudes (Northern Alaska, Canada, Northern Europe, Northern Russia, etc.). Very few temperature records exist in high elevations in these regions. Furthermore, the temperatures do not extend back very far in time. So, it is challenging for scientists to develop a long-term perspective on glacier health in these areas.

And this is why a new study attracted my attention. A paper was just published by the American Geophysical Union that shared research carried out by Dominic Winski and his colleagues.

This team of researchers extracted ice cores from the glaciers on Mt. Hunter, in Alaska. The ice cores held snow and ice from as far back as 400 years. The researchers showed that the amount of water melt currently is 60 times greater than it was prior to 1850. They also found that the summertime temperature changes on Mt. Hunter are almost 2°C per century (about 3.5°F). To put this in perspective, the temperatures are rising about twice as fast as global temperatures. [more]

Glacier loss is accelerating because of global warming

ABSTRACT: Warming in high‐elevation regions has societally important impacts on glacier mass balance, water resources, and sensitive alpine ecosystems, yet very few high‐elevation temperature records exist from the middle or high latitudes. While a variety of paleoproxy records provide critical temperature records from low elevations over recent centuries, melt layers preserved in alpine glaciers present an opportunity to develop calibrated, annually resolved temperature records from high elevations. Here we present a 400‐year temperature proxy record based on the melt layer stratigraphy of two ice cores collected from Mt. Hunter in Denali National Park in the central Alaska Range. The ice core record shows a sixtyfold increase in water equivalent total annual melt between the preindustrial period (before 1850 Common Era) and present day. We calibrate the melt record to summer temperatures based on weather station data from the ice core drill site and find that the increase in melt production represents a summer warming rate of at least 1.92 ± 0.31°C per century during the last 100 years, exceeding rates of temperature increase at most low‐elevation sites in Alaska. The Mt. Hunter melt layer record is significantly (p < 0.05) correlated with surface temperatures in the central tropical Pacific through a Rossby wave‐like pattern that enhances high temperatures over Alaska. Our results show that rapid alpine warming has taken place in the Alaska Range for at least a century and that conditions in the tropical oceans contribute to this warming.

A 400‐Year Ice Core Melt Layer Record of Summertime Warming in the Alaska Range



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