Global population-weighted degree-day projections for a combination of climate and socio-economic scenarios

Abstract

The projected global temperature increase in the 21st century is expected to have consequences on energy consumption due to increase (decrease) in energy demand to cool (heat) the built environments. Such increase (decrease) also depends on the number of end users for such energy, thus it is crucial to include population into the analyses. This study presents population-weighted (w) cooling (CDD), heating (HDD), and energy (EDD) degree-day projections at global, regional, and local scales for the 21st century. We used a large ensemble of high-resolution (0.44°) climate simulations from the COordinated Regional-climate Downscaling EXperiment (CORDEX) to compute degree-days for baseline (1981–2010) and global warming levels (GWLs from 1.5°C to 4°C), based on two representative concentration pathways. We used population projections from the NASA-SEDAC datasets, driven by five socio-economic scenarios (SSPs). The progressive increase in CDD outbalances the decrease in HDD in Central and South America, Africa, and Oceania and the opposite situation is likely to occur in North America, Europe, and Asia; at global scale, they are balanced. However, if results are weighted according to population, the increase in wCDD outbalances the decrease in wHDD almost everywhere for most GWLs and SSPs. Few regions show a decreasing tendency in wEDD at high GWLs for all SSPs: central Europe, northwestern, northeastern, and eastern Asia. Globally, wEDD are likely to double at 2°C compared to 1981–2010 independently of the SSP. Under the worst-case scenario (SSP3), at 4°C wCDD are approximately 380% higher and wHDD approximately 30% lower than in the recent past, leading to an increase in wEDD close to 300%.