# A Review of Worldwide Strategies for Promoting High-Temperature Heat Pumps
## 1 Introduction  
### Setting the Context  
Over the decades, numerous studies have documented the environmental impacts of climate change, including rising sea levels, increasing temperatures, more extreme weather events, and a higher incidence of droughts, flooding, and wildfires. These changes have led to significant health consequences for humans. Environmental alterations have been linked to a rise in infectious diseases, respiratory disorders, heat-related illnesses and deaths, undernutrition due to food insecurity, and adverse health outcomes stemming from increased sociopolitical tension and conflicts [1]. Furthermore, reducing dependence on fossil fuels is essential to mitigate global political and economic instability caused by their uneven geographical distribution. Many regions rich in fossil resources are also conflict zones, increasing the insecurity of supply for countries lacking energy independence. This reliance leads to fluctuations in fuel prices, destabilizing economies and political balances worldwide. For instance, in August 2022,the European Union (EU) experienced an unprecedented spike in gas prices, with increases of 1000% compared to previous decades. Over the past ten years, average gas prices ranged from 5 to 35 EUR/MWh, but in August 2022, Title Transfer Facility (TTF) derivative prices soared to a record high of 300 EUR/MWh, adversely affecting the EU economy [2]. However, the market price of fossil fuels does not fully account for the costs associated with their consumption. Due to this aspect, many national and subnational jurisdictions have implemented mechanisms to price pollutant emissions, aiming to address this discrepancy [3]. By implementing emissions pricing mechanisms, the cost of using polluting fuels increases, making them less attractive compared to greener alternatives. This approach ensures that the cost of emissions is directly attributed to the emitter. In 2022, this principle highlighted a troubling trend. Emissions reached a record high of 53.8 Gt CO\({}_{2}\)eq, approximately 1.4% more than in 2021, making it the year with the highest level of recorded emissions. Around two-thirds of these emissions originated from just six countries: China (29.2%), the United States (11.2%), India (7.3%), the EU27 (6.7%), Russia (4.8%), and Brazil (2.4%), as shown in Figure 1a. Figure 1b illustrates these emissions, highlighting that CO\({}_{2}\) is the predominant contaminant emitted by the six countries, except for Brazil, where methane accounts for about 51% of total emissions. Globally, CO\({}_{2}\) constitutes 71.6% of total emissions, followed by methane (CH\({}_{4}\)) at 21%, nitrous oxide (N\({}_{2}\)O) at 4.8%, and fluorinated gases (F-gases) at 2.6% [4; 5]. Many jurisdictions, both national and subnational, have introduced carbon pricing measures to incentivize progress toward established decarbonization goals. The most widespread mechanisms are the Emission Trading System (ETS), adopted by 37 jurisdictions, and the carbon tax (CT), also implemented by 37 jurisdictions [3]. In both cases, the product's cost increases as the emissions from its production rise. The ETS mechanism, known as \"cap and trade\", involves setting a maximum limit, or \"cap\", on the total amount of greenhouse (GHG) gases that covered installations and aircraft operators can emit. This cap is gradually reduced over time, and it is quantified in terms of emission allowances, with each allowance representing the right to emit one metric ton of carbon dioxide equivalent (CO\({}_{2}\)eq). Companies within the system must surrender enough allowances annually to cover their emissions completely. Failure to do so results in significant fines. Additionally, within the system, it is also allowed to trade emissions allowances such that if a company reduces its emissions below its allocated allowances, it can either save the surplus for future use or sell them to other entities [6].