Drivers of modern New Zealand glacier change

<p>Glaciers across the Southern Alps of New Zealand have been photographed annually since 1977, creating a rare record of Southern Hemisphere glacier change. Here, we revisit these historic photographs and use structure from motion photogrammetry to quantitatively measure glacier change from the images. To establish this new method, it is initially applied to Brewster Glacier (1670 – 2400 m a.s.l.), one of the 50 monitored glaciers. We derive annual equilibrium line altitude (ELA) and length records from 1981 – 2017, and quantify the uncertainties associated with the method. Our length reconstruction shows largely continuous terminus retreat of 365 ± 12 m for Brewster Glacier since 1981. The ELA record, which compares well with glaciological mass-balance data measured between 2005 and 2015, shows pronounced interannual variability. Mean ELAs range from 1707 ± 6 m a.s.l. to 2303 ± 5 m a.s.l. The newly developed ELA chronology from Brewster shows several years since 1981 with especially high mass loss, all of which occurred in the past decade. Investigation using reanalysis data shows that these extreme mass-loss years occur when surface air temperatures, sea surface temperatures, and mean sea level pressure are anomalously high. In particular, the three highest mass-loss years on record, 2011, 2016, and 2018, each had a 2-month mean surface air temperature anomaly of at least +1.7°C between November and March, which is exclusive to these three years over the time investigated (April 1980 – March 2018). Using event attribution — a methodology using climate model simulations with and without human-induced forcings to calculate the anthropogenic influence on extreme events — we calculate the anthropogenic influence on these surface air temperature anomalies. The positive temperature anomalies during extreme mass-loss years have probabilities of 0 – 90% confidence) more likely to occur with anthropogenic forcing, and in once case in 2018 could not have occurred (>90% confidence) without anthropogenic forcing. This increased likelihood is driven by present-day temperatures ~1.0°C above the pre-industrial average, confirming a connection between rising anthropogenic greenhouse gases, warming temperatures, and high annual ice loss.</p>

Drivers of modern New Zealand glacier change

<p>Glaciers across the Southern Alps of New Zealand have been photographed annually since 1977, creating a rare record of Southern Hemisphere glacier change. Here, we revisit these historic photographs and use structure from motion photogrammetry to quantitatively measure glacier change from the images. To establish this new method, it is initially applied to Brewster Glacier (1670 – 2400 m a.s.l.), one of the 50 monitored glaciers. We derive annual equilibrium line altitude (ELA) and length records from 1981 – 2017, and quantify the uncertainties associated with the method. Our length reconstruction shows largely continuous terminus retreat of 365 ± 12 m for Brewster Glacier since 1981. The ELA record, which compares well with glaciological mass-balance data measured between 2005 and 2015, shows pronounced interannual variability. Mean ELAs range from 1707 ± 6 m a.s.l. to 2303 ± 5 m a.s.l. The newly developed ELA chronology from Brewster shows several years since 1981 with especially high mass loss, all of which occurred in the past decade. Investigation using reanalysis data shows that these extreme mass-loss years occur when surface air temperatures, sea surface temperatures, and mean sea level pressure are anomalously high. In particular, the three highest mass-loss years on record, 2011, 2016, and 2018, each had a 2-month mean surface air temperature anomaly of at least +1.7°C between November and March, which is exclusive to these three years over the time investigated (April 1980 – March 2018). Using event attribution — a methodology using climate model simulations with and without human-induced forcings to calculate the anthropogenic influence on extreme events — we calculate the anthropogenic influence on these surface air temperature anomalies. The positive temperature anomalies during extreme mass-loss years have probabilities of 0 – 90% confidence) more likely to occur with anthropogenic forcing, and in once case in 2018 could not have occurred (>90% confidence) without anthropogenic forcing. This increased likelihood is driven by present-day temperatures ~1.0°C above the pre-industrial average, confirming a connection between rising anthropogenic greenhouse gases, warming temperatures, and high annual ice loss.</p>

Glacial Deaths, Geologic Extinction

In 2019 several funerals were held for glaciers. If enough glaciers die, could they go extinct? Is there geologic extinction? Yes. This article develops three arguments to support this claim. The first revisits Georges Cuvier’s original argument for extinction and its reliance on geology, especially glaciers. Retracing connections to glaciers and the narrowing of extinction to biological species in the nineteenth century, the author argues that anthropogenic forcing on how the Earth system functions—the Anthropocene—warrants rethinking extinction geologically. The second argument examines the specificity of ice loss and multiple practices responding to this loss: from art exhibits at United Nations climate change meetings to anticolonial claims for the right to be cold. The third argument consolidates a theme built across the article regarding how Isabelle Stengers’s notion of ecologies of practices provides an approach to geologic extinction that recognizes both relational and nonrelational loss.

Poleward migration of western North Pacific tropical cyclones related to changes in cyclone seasonality

The average location of observed western North Pacific (WNP) tropical cyclones (TCs) has shifted north over the last several decades, but the cause remains not fully understood. Here we show that, for the annual average, the observed northward migration of WNP TCs is related to changes in TC seasonality, not to a northward migration in all seasons. Normally, peak-season (July–September) TCs form and travel further north than late-season (October–December) TCs. In recent decades, related to less frequent late-season TCs, seasonally higher-latitude TCs contribute relatively more to the annual-average location and seasonally lower-latitude TCs contribute less. We show that the change in TC seasonality is related to the different responses of late-season and peak-season TC occurrence to a stronger Pacific Walker Circulation. Our findings provide a perspective on long-term trends in TC activity, by decomposing the annual-average statistics into seasonal components, which could respond differently to anthropogenic forcing.