Abstract
Abstract. The Swedish Meteorological and Hydrological Institute used the global climate model EC-Earth3 to perform a large ensemble of simulations (SMHI-LENS). It consists of 50 members, covers the period 1970 to 2100, and comprises the SSP1-1.9, SSP3-3.4, SSP5-3.4-OS, and SSP5-8.5 scenarios. Thus, it is currently the only large ensemble that allows for analyzing the effect of delayed mitigation actions versus no mitigation efforts and versus earlier efforts leading to similar radiative forcing at the year 2100. We describe the set-up of the SMHI-LENS in detail and provide first examples of its application. The ensemble mean future changes in key variables in the atmosphere and ocean are analyzed and compared against the variability across the ensemble members. In agreement with other large-ensemble simulations, we find that the future changes in the near-surface temperature are more robust than those for precipitation or sea level pressure. As an example of a possible application of the SMHI-LENS, we analyze the probability of exceeding specific global surface warming levels in the different scenarios. None of the scenarios is able to keep global warming in the 21st century below 1.5 ∘C. In SSP1-1.9 there is a probability of approximately 70 % to stay below 2 ∘C warming, while all other SSPs exceed this target in every single member of SMHI-LENS during the course of the century. We also investigate the point in time when the SSP5-8.5 and SSP5-3.4 ensembles separate, i.e., when their differences become significant, and likewise when the SSP5-3.4-OS and SSP4-3.4 ensembles become similar. Last, we show that the time of emergence of a separation between different scenarios can vary by several decades when reducing the ensemble size to 10 members.
Highlights
Global climate is changing due to anthropogenic greenhouse gas emissions (IPCC 2013), and global mean temperature has already increased by more than 1 ◦C compared to preindustrial temperature levels
We find a distinct impact on the Atlantic Meridional Overturning Circulation (AMOC) that first weakens compared to present-day conditions but partly recovers in all scenarios except for the high-end SSP5-8.5 scenario (Fig. 2c)
We have presented an overview of the SMHI Large Ensemble that consists of 50 members done with the EC-Earth3 model
Summary
Global climate is changing due to anthropogenic greenhouse gas emissions (IPCC 2013), and global mean temperature has already increased by more than 1 ◦C compared to preindustrial temperature levels. The observed temperature time series show large variations on top of the warming trend, resulting in periods of up to decades with reduced or accelerated temperature increase. Changes in climate forcing parameters such as solar irradiance or aerosols and internal climate variability contribute to this observed variability. At the regional level, internal variability leads to large uncertainties on timescales up to several decades (e.g., Hawkins and Sutton, 2009; Hawkins, 2011). Longterm station observations at different places across Europe show large internal variability of temperature (Moberg et al, 2000). Observations from Uppsala in Sweden, Europe’s longest continuous temperature time series, show that 30year mean winter temperature has varied by several degrees Celsius between different observed 30-year periods (Moberg and Bergström, 1997). Internal climate variability contributes to uncertainties in future climate projections. In agreement with this, Marotzke (2019) found that internal variabil-
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