[MCN] Confirmed, again: Heat dims outlook for future of snow

Lance Olsen lance at wildrockies.org
Wed Apr 19 10:13:22 EDT 2017


Nature Communications Published online:18 April 2017

 Large near-term projected snowpack loss over the western United States

John C. Fyfe et al
 
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“In this study, we show that losses in regional snowpack over the past few decades are consistent with natural and anthropogenic changes, but are inconsistent with natural changes alone. We predict an additional loss of snowpack water storage of up to 60% within the next three decades due to combined influences from anthropogenic forcing and internal decadal variability.”

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Abstract [open access]
https://www.nature.com/articles/ncomms14996 <https://www.nature.com/articles/ncomms14996>

 Peak runoff in streams and rivers of the western United States is strongly influenced by melting of accumulated mountain snowpack. A significant decline in this resource has a direct connection to streamflow, with substantial economic and societal impacts. Observations and reanalyses indicate that between the 1980s and 2000s, there was a 10–20% loss in the annual maximum amount of water contained in the region’s snowpack. Here we show that this loss is consistent with results from a large ensemble of climate simulations forced with natural and anthropogenic changes, but is inconsistent with simulations forced by natural changes alone. A further loss of up to 60% is projected within the next 30 years. Uncertainties in loss estimates depend on the size and the rate of response to continued anthropogenic forcing and the magnitude and phasing of internal decadal variability. The projected losses have serious implications for the hydropower, municipal and agricultural sectors in the region.
 

Introduction

Introduction

It is well established that the North American continent is warming1 <https://www.nature.com/articles/ncomms14996#ref1>, partly due to increasing emissions of well-mixed greenhouse gases2 <https://www.nature.com/articles/ncomms14996#ref2>. In the winter season, this warming contributed to snowpack loss over the western United States3 <https://www.nature.com/articles/ncomms14996#ref3>,4 <https://www.nature.com/articles/ncomms14996#ref4>,5 <https://www.nature.com/articles/ncomms14996#ref5>,6 <https://www.nature.com/articles/ncomms14996#ref6>. It is also well known that the region’s climate is substantially influenced by decadal variability originating in the adjacent Pacific Ocean7 <https://www.nature.com/articles/ncomms14996#ref7>. In this study we employ observations, land surface reanalyses and climate model simulations to characterize the combined influences of decadal variability and external forcing on recently observed and near-term projected changes in snowpack over the western United States.

Recognition of the pronounced influence of decadal variability on regional trends in climate is motivating efforts to generate large initial condition ensembles of global climate model simulations. These ensembles provide estimates of the relative contributions of internal variability and external forcing to regional-scale climate changes8 <https://www.nature.com/articles/ncomms14996#ref8>,9 <https://www.nature.com/articles/ncomms14996#ref9>,10 <https://www.nature.com/articles/ncomms14996#ref10>,11 <https://www.nature.com/articles/ncomms14996#ref11>. An initial condition ensemble consists of many individual simulations performed with a given coupled climate model; each simulation uses the same external forcing, but is initiated from slightly different conditions of the atmosphere and/or ocean state. Each ensemble member has a different realization of internal variability superimposed on the underlying externally forced response. 

Because of their high computational cost, large (>10-member) ensembles are rare. It is also rare for groups to perform multiple large ensembles, one consisting of simulations with anthropogenic forcing only, and one with simulations incorporating solar and volcanic forcing alone. Here, we generate and analyse 50-member anthropogenic and naturally forced ensembles. We also rely on a large ensemble of higher-resolution regional climate model simulations driven with the output from the global climate model.

Although several studies have found an anthropogenic contribution to snowpack loss over the western United States, the combined influences of decadal variability and external forcing remain poorly quantified in observations and near-term projections. In this study, we show that losses in regional snowpack over the past few decades are consistent with natural and anthropogenic changes, but are inconsistent with natural changes alone. We predict an additional loss of snowpack water storage of up to 60% within the next three decades due to combined influences from anthropogenic forcing and internal decadal variability.

Complete article here:

https://www.nature.com/articles/ncomms14996 <https://www.nature.com/articles/ncomms14996>

 

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"Ignorance of remote causes disposeth men to attribute all events to the causes immediate and instrumental: for these are all the causes they perceive."

Attributed  to Thomas Hobbes
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“Making connections is the essence of scientific progress.”

Chris Quigg, “Aesthetic Science,”  Scientific American, April 1999
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“Teleconnections can be defined as linkages between climate anomalies at some distance from each other. The large distances in space and the differences in timing between these anomalous events make it difficult for one to believe that one event (El Nino or La Nina) could possibly have influence on the other (e.g. drought in southern Africa or hurricanes in the tropical Atlantic). Nevertheless, physical and statistical research has shown that such linkages do exist.”

Michael Glantz. Currents of Change : Impacts of El Nino and La Nina on Climate and Society. Cambridge University Press, 2001

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