Elsevier

Applied Geography

Volume 119, June 2020, 102216
Applied Geography

Impacts of Greenland and Antarctic Ice Sheet melt on future Köppen climate zone changes simulated by an atmospheric and oceanic general circulation model

https://doi.org/10.1016/j.apgeog.2020.102216Get rights and content

Highlights

  • Assess impacts of ice sheets melting on GCM simulations using Koppen classification.

  • Freshwater from Greenland/Antarctica influences changes already induced by RCP8.5

  • Precipitation changes have major impacts on the climate in the Southern Hemisphere.

  • Temperature changes strongly impact the climate in the Northern Hemisphere.

  • Importance of ice sheet meltings in climate projections causing model uncertainty.

Abstract

Climate change studies in recent decades have been based on Global Climate Models (GCMs), and the changes in the distribution of climatic regions over time extracted from these models can be represented using the Köppen climatic classification system, which predicts the global distribution of biomes based on monthly precipitation and average temperatures. In this study, the Köppen classification is used to evaluate the impacts of the melting of the Greenland and Antarctic Ice Sheets on GCM simulation results, on regional and global scales. To assess the impacts of accelerated ice sheet melting, an approach is utilized which is based on numerical simulations from the IPSL-CM5A-LR GCM; here, freshwater is introduced near the ice sheets and is superimposed on the RCP8.5 scenario. The changes in the distribution of the Köppen climatic regions under various scenarios (a historical run from observations, RCP8.5, and various examples of polar ice sheet melting) and comparisons between them reveal that major changes will occur on the global scale during the period 2041–2060. The analysis of group shifts within the Köppen classification system reveals that when freshwater from Greenland or Antarctica is introduced into the ocean, the inter-tropical belt undergoes greater change than it does under the RCP8.5 scenario. A focus on sub-group shifts within the Koppen classification system shows that changes in precipitation have major impacts on the climate in the Southern Hemisphere. Further, the changes are more drastic if the freshwater originates from Greenland than from Antarctica or from both locations. However, changes in temperature strongly impact the climate in the Northern Hemisphere and are significantly affected by the melting of the Greenland Ice Sheet. This study highlights the importance of considering ice sheet melting in the modeling of future global climate.

Introduction

Climate change and its impacts on society and ecosystems have been investigated in recent decades using Global Climate Models (GCMs), which provide projections of future climate under various emission scenarios (Delworth et al., 2006; Manabe & Stouffer, 1980; McGuffie et al., 1999; Moss et al., 2010; Semenov & Stratonovitch, 2010). The Representative Concentration Pathways (RCPs) are a collection of CO2 emission pathways corresponding to radiative forcing in 2100 (see Taylor, Stouffer, & Meehl, 2012) within the framework of the Coupled Model Intercomparison Project (CMIP5, Meehl, Boer, Covey, Latif, & Stouffer, 2000).

Driven by climate change, polar ice sheet melting is accelerating, resulting in a massive input of freshwater into the oceans (Peterson et al., 2006; Rignot, Velicogna, van den Broeke, Monaghan, & Lenaerts, 2011). Recently, several studies have shown that some mechanisms can accelerate the contribution of freshwater from the ice sheets into the ocean (Rignot, Fenty, Xu, Cai, & Kemp, 2015; Straneo et al., 2013). Even though some climate models in the CMIP5 exercises include the melting of ice sheets (Church et al., 2013), the most recent publications show that ice sheet melting is more important than previously suspected (i.e., IPCC report; Gillet-Chaulet et al., 2012). However, a recent review showed that under the 2 °C warming scenarios, ice sheet melting is irreversible and will accelerate during the 21st century (Pattyn et al., 2018). Various studies have shown that this process has already affected past and present climatic dynamics (Dahl-Jensen et al., 1998; Hansen et al., 2016; Swingedouw et al., 2008 and 2015). Although the details of future ice sheet meltwater input into the ocean will likely differ from past Heinrich events, these events can be considered analogous to future ice sheet mass loss in that both scenarios result in a large release of freshwater into the North Atlantic. During the Heinrich event, the supply of freshwater reduced thermohaline circulation in the North Atlantic by decreasing the density of the water, prohibiting it from sinking to the bottom of the ocean. This phenomenon reduced the surface circulation of the North Atlantic current (AMOC) and therefore decreased the heat supply to the North Pole. Some of the available heat accumulated in the South Atlantic (seesaw effect, Stocker, 1998), while some of the heat was transferred to the atmosphere (Bjerknes effect, Outten, Esau, & Otterå, 2018). The consequences were a cooler Northern Hemisphere and a warmer Southern Hemisphere. During the Last Glacial Maximum, there were many consequences of the slowdown of the AMOC.

The decrease in the rate of thermal energy transfer to the North Pole resulted in a decrease in temperature in Europe (Guiot et al., 1993) and North America (Grimm, Jacobson, Watts, Hansen, & Maasch, 1993). Paleoclimatic surveys and numerical modeling experiments show a weakening of the monsoons in Africa (Mulitza et al., 2008) due to the slowdown of the AMOC, inducing a decrease in temperature in the Sahara and an increase in temperature in the Guinea Gulf. This slowdown also impacted the monsoons in India (Marzin, Braconnot, & Kageyama, 2013). An increase in the El Niño–Southern Oscillation (ENSO) amplitude occurred, because the slowing of the AMOC stimulated a transfer of heat across the Panama isthmus to the Pacific Ocean (Luan, Braconnot, Yu, & Zheng, 2015). Finally, the modification of ENSO generated more rainfall in Australia (Denniston et al., 2013) and an intensification of rainfall in Amazonia (Lewis, LeGrande, Kelley, & Schmidt, 2010). Not accounting for these mechanisms in future projections may thus lead to overlooking serious consequences of climate change. In our research, we used a simulation approach developed by Defrance et al. (2017) to test the effects of freshwater input from ice sheet melting on climatic changes under the RCP8.5 scenario.

Beyond a simple analysis of the GCMs’ outputs, an integrative approach based on bioclimatic classification can be used to give an ecological understanding of the combined changes in climate variables and to assess how the location and extent (surface area) of present climatic regions will evolve over time (e.g., Trewartha & Horn, 1980; Kalvová, Halenka, Bezpalcová, & Nemešová, 2003; Feng et al., 2014; Belda, Holtanová, Halenka, Kalvová, & Hlávka, 2015). The Köppen climate classification is the most widely used classification method (Rajaud & de Noblet-Ducoudré, 2017; Rubel & Kottek, 2010). Based on expert knowledge of the climatic conditions that cause generic biomes, it defines a set of climatic regions separated by empirical thresholds of temperature and rainfall. These are used to predict the distribution of biomes worldwide based on the monthly cumulative precipitation, the monthly mean air temperature, and the relationship between climate and vegetation (Köppen, 1900, 1923, 1931, and 1936; Geiger, 1954; Fraedrich, Gerstengarbe, & Werner, 2001; Rubel & Kottek, 2010). The ability to reproduce observed geographical biome patterns using the Köppen climate classification has been validated by Rohli, Joyner, Reynolds, & Ballinger (2015). This classification has been used to study climatic shifts in many regions (Fraedrich et al., 2001; Rajaud & de Noblet-Ducoudré, 2017; Rubel & Kottek, 2010). Following a similar approach, Thornthwaite developed a climate classification that includes refined delimitation criteria. Although more recent, its higher level of complexity makes it more difficult to apply and interpret, and it is much less commonly used than the Köppen classification (Feddema, 2005). An alternative approach to studying climatic changes is to engage in statistical clustering over a larger ensemble of climate variables (Metzger et al., 2013). However, the ecological significance of the statistical partition thus produced can only be validated through a comparison with a reference, which is often the Köppen classification. We followed the most common approach and used the Köppen classification.

In this study, the impacts of freshwater inputs from the Greenland and/or Antarctic Ice Sheet melting through the end of the 21st century under the RCP8.5 scenario are compared based on:

  • the simulated global evolution of temperature and precipitation;

  • the distribution and shifts of climatic regions on a global scale using the Köppen classification;

  • the regional trends of climatic evolution in South America, Africa, and Australia, which are complementary to the results obtained by Defrance et al. (2017) for West Africa, who used the same approach.

Section snippets

Climate model and experimental design

The experimental design used in this study is based on the methodological approach developed by Defrance et al. (2017), which is summarized in Fig. 1.

All the experiments were conducted using the coupled atmosphere-ocean IPSL-CM5A-LR model (Dufresne et al., 2013), which was also used for the CMIP5 exercises (Taylor et al., 2012). IPSL-CM5A-LR contains biogeochemistry models (from the troposphere to the deep ocean) and physical models (atmosphere, land surface, ocean, and sea-ice). CO2 and other

Global changes in temperature and precipitation

Fig. 2a shows the mean annual temperature over the period 1986–2005 (considered to be the historical run). Fig. 2b, c, and d show the variations in the global temperature with respect to the historical run over the period 2041–2060 under the RCP8.5, GrIS 3 m, and WAIS 3 m scenarios. Other scenarios are introduced in the Supplementary Materials (SI2 and S13). For the RCP8.5 case, the maximum variations in the temperature, which reach 5–10 °C locally, are observed in the Northern Hemisphere at

Discussion

In this study, the Köppen classification is used to assess the consequences of an acceleration in ice sheet melting through the end of the 21st century using the IPSL-CM5A-LR model. To simulate the melting, freshwater is introduced into the North Atlantic or around West Antarctica and is superimposed on the RCP8.5 scenario. Based on the monthly average temperature and cumulative precipitation, we obtain a reasonable fit to the Köppen classification by comparing observations (EWEMBI) with

Conclusion

The consequences of the Heinrich events, which occurred during the Last Glacial Maximum, warned of future climatic consequences of accelerated ice sheet melt. Since the last IPCC report (AR5), several studies have shown that the ice sheets melt faster than previously predicted and might induce global climatic change beyond sea level rise.

Using the IPSL-CM5A-LR climate model, we studied the impacts of accelerated ice sheet melting on 21st century climate change. Using the Köppen classification,

CRediT authorship contribution statement

Dimitri Defrance: Conceptualization, Investigation, Writing - original draft, Methodology. Thibault Catry: Investigation, Writing - original draft, Visualization. Amélie Rajaud: Methodology. Nadine Dessay: Investigation. Benjamin Sultan: Supervision.

Acknowledgements

This study benefited from the high-performance computing (HPC) resources made available by The Grand Equipement National de Calcul Intensif, CEA, and Centre National de la Recherche Scientifique.

The EWEMBI dataset can be found at.

http://dataservices.gfz-potsdam.de/pik/showshort.php?id=escidoc:1809891.

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