The share of cooling electricity in global warming: Estimation of the loop gain for the positive feedback

Highlights

• Electricity need for cooling buildings in summers is estimated for 12 world regions.

• Carbon emitted by fossil-fuel power plants for the cooling electricity is estimated.

• A linear model is used to relate emissions to the land temperature anomaly.

• Loop-gain is estimated then by multiplying the two estimated coefficients.

• The positive loop will bring up acceleration again even in optimistic scenarios.

Abstract

Our world's future is strongly connected to energy consumption trends. There are bi-directional relations between energy consumption and the average temperature of Earth, leading to positive causal loops. Increasing temperatures cause activity of more cooling systems most of which are electrified by burning hydrocarbons that consequently yield more carbon dioxide concentration and warmer climates. This paper is a trial to estimate the loop gain by employing a bottom-up regional model. The model is a spreadsheet containing sets of parameters and variables to estimate electricity used for cooling buildings in the residential and commercial sectors of 12 regions all around the world. The share of fossil-fuel based power plants determines each region's contribution to CO₂ emissions. Then, by processing data on the global emission trend and land temperature anomaly, a linear ARMAX relationship is estimated to compute the loop gain. The results show that, even in the optimistic scenario of IPCC (A1B), emission from cooling electricity will double up by the end of the century. With the estimated 1 + 1.4 × 10^-6 loop gain, even if fossil-fuel electricity generation is gradually reduced to 40%, after a short fall, it will start growing again in the mid-century.

Introduction

Nowadays, nobody can neglect the global warming phenomenon, since most people can sense and see its consequences in all seasons of their life. Climate change acceleration has been a serious concern of researchers for decades [1]. The intergovernmental panel for climate change predicted that the average temperature of our planet will increase by 1.4–5.8 °C by the end of the 21st century [2]. There are researches that propose more pessimistic estimates [3]. The warming speed has been estimated at more than 0.02 °C per year for recent decades. Some researchers estimate the global warming from 1850 conditions to 2080–2100 ranges from 1.5 °C to 4.4 °C under different scenarios [2]. They also address recent acceleration in warming. There exist an extensive literature that discusses the phenomenon by large models, among from System Dynamics (SD) models are of interest [4], used for policy analyses too [5].

The acceleration is probably because of positive feedbacks in the entire carbon concentration system addressed in the literature [3], some of which are represented by Fig. 1. Three main resources of carbon dioxide are supplying the fuel for a long-term dynamics of this system: solar radiation, CO₂ emitted by volcanic activities, and the only anthropological one, i.e. fuel burning by human beings. The first loop, denoted by + R1, which accelerates solar radiation absorption, is the effect of temperature rise on the polar ice melting, as well as fewer winter snows cover, which in turn causes expansion of oceans and more darkness of Earth's surface [6]. The second, +R2, is in fact inside the first; even more ocean expansion is in progress because of more waves and storms that eat the shores. Although the oceans act as a giant lung that absorbs CO₂, scientists have found that its performance is a function of the atmosphere temperature. Thus, a third positive loop is activated weakening Earth's lungs and reduces both land and ocean uptake of CO₂, respectively by 54% and 35%, if the CO₂ concentration is four folds [7]. The fourth positive loop has been also warned by scientists several times. The warming atmosphere speeds up the decomposition of belowground organic matter [8]. This also leads to more greenhouse gases (GHG) released into the atmosphere and closes another positive loop, +R4. The next positive loop, +R5, accelerates deforestation, including two other re-enforcing loops that worsen the case by decreasing rainfalls [9].

Before explaining the simple sixth loop, it is worth mentioning how critical is to study the dynamics of these loops. Although many articles have been modeling and analyzing the climate change phenomenon [10], not any paper has quantitatively discussed how exactly these loops affect climate change acceleration. Nonetheless, there are few papers that have estimated one of the individual loop gains, mostly focusing on the third loop. However, wild rapid changes, nonlinearities, and the complicated dynamics have made the researchers to revise and correct their estimates frequently [11].

The Global Carbon Project organization publishes the most recent reports revealing various statistics such as trends for carbon emission (CE) and global warming, as well as predictions of what can happen under different scenarios. The conceptual framework including most of the above-mentioned loops plus some other could be found in reports of the organization which are provided by collaborative efforts of the global carbon cycle science community [12].

Research shows that climate change has an undeniable impact on electricity consumption. The increase of cooling energy demand in Switzerland [13], California [14], and the entire United States [15], studied by researchers, are just a few examples for evidence of such impact. The warmer is going the weather the more electrical energy is needed for cooling and the more fossil fuel is burned for electricity generation. For instance, it is shown by simulation that the peak cooling energy use will increase in the US about 7%–9% in 2020 w.r.t. 1960 [15]. Moreover, the more fuel is consumed for either heating or cooling by electricity, the more important its side effects appear in the climate, i.e. the CO₂ emission, global warming, and climate change [16]. This paper aims to analyze one of the factors of the warming acceleration represented by Fig. 2.

On one hand, there are limited resources of energy, mostly fossil fuels. On the other hand, using fossil energy resources for both cooling and heating, with the consequence of CO₂ emission, causes the average temperature of Earth to increase [17]. Fig. 2 shows this mechanism in three loops. Energy consumed for cooling emits CO₂ that accelerates warming in the middle loop, while in the left side loop, the energy required for heating decreases for the fact that the average temperature has a positive trend. In System Dynamics methodology these are called reinforcing and balancing loops respectively. Apparently, all reinforcing loops exacerbate the problem in the future of the global climate. Focusing solely on the positive trend, other probable positive loops due to colder winters and hotter summers, which are counted as a consequence of meandering phenomenon in jet streams [18], are not shown in these figures and need separate research to conclude their effects.

Hence, researchers ought to think for any solution that adjusts the middle loop with a negative effect and attenuates the corresponding positive gain as much as possible.

Regarding the positive loop, one can make a rough calculation that energy needed for keeping a 100 m² sample house 1 °C colder than the outdoor temperature for an hour is approximately 0.5 kWh. This energy is mostly provided by electricity, which can be generated by fossil fuels or renewable (clean/carbonless) energies. Both technologies based on cooling by fossil fuel directly, or by fuel-based electric power cause CO₂ emission which in turn leads the average temperature of the globe to increase, and so need more energy for cooling. Moreover, other energy demand supplied by fossil fuel, especially in the industrial and transportation sectors, accelerates the warming loop even more. Adding these factors to Fig. 2 in its right-hand loop leads to what is presented by Fig. 3.

Since the energy required for heating is mostly demanded by industries that mainly use fossil fuels, the left-hand side balancing loop is too weak to compensate for the destabilizing effect of the other reinforcing loop. However, if electricity generated by renewable resources is promoted and increased, fossil fuels consumption will reduce, and the warming rate of the global climate will be lowered. Therefore, it seems essential to investigate climatic factors effect on energy consumption in two warm and cold seasons separately.

There are a few studies reporting estimates on the share of cooling electricity in the total electricity consumption all around the world. Although there are accurate engineering methods to calculate the heating/cooling loads, on large-scale, e.g. for a country, it is too difficult to estimate the total worldwide load by such detailed methods. Detailed bottom-up electricity demand estimates are performed for buildings of the European service sector [19], A household energy use breakdown is done in 2009 for the United States [20]. The researchers have found that almost 11% and 14.1% of electricity is consumed for cooling and air-conditioning in these two regions, respectively. Updates can be found for 2014 in Europe [21] and 2015 in the US [22], which refer to 13.7% and 18%, respectively. There are many other works that address how temperature and other climatic variables can impact electricity consumption, both from a technical viewpoint [23,24] or in a macro level for a specific city or country [25,26].

This paper aims to follow up a bottom-up analysis of electricity use in the world and then present a simple method for estimating the loop gain that is comparable with the results obtained by other top-down electricity demand models. An intelligent design of electricity demand model for a sample residential-commercial region [24,25,26,27,28,29,30,31], which includes climatic variables, particularly the temperature, might be used to estimate the total electricity used for cooling. The results are compared with those could be found in the literature to confirm the accuracy of the estimates. Finally, gathering data for the share of fossil-fuel based power plants, the total GHG emissions are calculated and then the global warming acceleration rate caused by cooling the residential-commercial sectors is estimated.

The organization of the paper is as follows. The second section is dedicated to the analysis of electricity demand for space cooling through a bottom-up approximate, yet complicated and efficient model. It is tried to relate almost everything to the temperature. Then the calculation is tracked for a sample region and the results are summarized for 12 regions of the world. In the next section, by using linear approximate models the relationship between GHG emission and the average global temperature anomaly is estimated, where the loop gain is found. A long-term simulation is also designed in two scenarios and the results are compared. Section four concludes the paper.