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• Heating and cooling changes in the past and in the future To quantify the magnitude of past and future changes , we use the absolute differences in the heating and cooling proxies between 1981 – 2000 and 1941 – 1960 , henceforth referred to as past changes , and between 2021 – 2040 and 1981 – 2000 , henceforth referred to as future changes .
We estimate the heating and cooling proxies from the CMIP5 historical simulations for the past and from the projections using the Representative Concentration Pathway 8.5 ( RCP8.5 ; unless otherwise stated ) for the future . The MMM heating proxy decreased and the MMM cooling proxy increased over the course of both the past and the future time periods .
In the past , the most important changes in the heating proxy ( below −200 HDD ) occurred over polar regions ( Fig . 1a ), while , in the future , a decrease in the heating proxy of at least this magnitude occurs over the entire Northern Hemisphere ( Fig . 1b ). The increase in the cooling proxy was small in the past , below + 100 CDD , everywhere except in some ( semi- ) arid parts of West Africa ( Fig . 1c ).
The projected future increase in the cooling proxy , on the other hand , exceeds + 100 CDD in most of the mid-latitude regions , exceeds + 300 CDD in large parts of the tropics , and exceeds + 400 CDD in Amazonia , in parts of the Sahel and in the Arabian Peninsula ( Fig . 1d ).
Changes in the heating and cooling proxies have similar spatial patterns in the past and the future , with an overall extension of the areas with significant changes projected for the future ( Fig . 1a , c compared to Fig . 1b , d ). Mid-latitude regions present significant changes in both the heating and the cooling proxies .
Areas with non-significant changes in the heating proxy are projected to reduce to tropical ocean regions , including tropical islands , as well as Amazonia in the future ( Fig . 1b ). Conversely , areas with non-significant changes in the cooling proxy are projected to reduce to the northern ( above 40 ° N ) and southern ( below 40 ° S ) oceans , whereas there is a significant change over all continental areas ( except Greenland and Antarctica ) in the future ( Fig . 1d ).
• Comparing trends in heating and cooling Even when the absolute differences in some regions are small from one period to another , they could lead to significant changes in societal behaviour , such as widespread acquisition of cooling systems , as people feel a difference in thermal comfort relative to the past . We quantify trends in climate-driven energy demand for heating and cooling buildings by computing the relative differences in our proxies for the past and the future ( cf . Methods section ), which leads to important trends in the
Images by Nature Communications
Fig . 1 : Global climate-driven changes in energy demand for heating and cooling buildings .
Fig . 2 : Global climate-driven trends in energy demand for heating and cooling buildings .
surroundings of the areas with non-significant changes ( grey shaded areas in Fig . 1 ).
Over continental areas , the decreasing trend in the MMM heating proxy was weak , ranging from −20 to 0 % in the past ( Fig . 2a ). This trend is projected to become clearly negative everywhere in the future , reaching at least −5 % ( Fig . 2b ).
The increasing trend in the MMM cooling proxy was weak in the past , ranging between 0 and + 20 % over continental areas ( Fig . 2c ). This trend is also projected to be more pronounced in the future , exceeding + 10 % everywhere , reaching at least + 20 % over mid-latitude regions , and more than + 60 % in many northern hemisphere regions ( Fig . 2d ).
Over mid-latitude oceans , the projected trend in the cooling proxy is to exceed + 100 %, which leads to strong gradients close to the coastlines , where an important part of the population lives .
Notes : This is an extract of the full paper available on nature . com – Article number : 5197 ( 2021 ). Re-published under creative commons license . RACA
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