# A Review of Worldwide Strategies for Promoting High-Temperature Heat Pumps
## 1 Introduction
### Setting the Context
In 2015, the Paris Agreement emerged as a pivotal milestone in global climate action. This legally binding international treaty, effective since November 2016 and ratified by 195 Parties, sets forth long-term objectives to steer nations toward substantial reductions in global GHG emissions. It aims to keep the increase in global temperature well below 2 \({}^{\circ}\)above pre-industrial levels, with efforts to limit the increase to 1.5 \({}^{\circ}\)C. Central to the Paris Agreement are provisions for periodic assessments of collective progress and the provision of financial support to developing countries for climate mitigation, resilience building, and adaptation. This framework lays the groundwork for concerted efforts towards a net-zero emissions future, a cornerstone for achieving Sustainable Development Goals (SDGs). Operating on a five-year cycle, the agreement mandates countries to update their national climate action plans, known as Nationally Determined Contributions (NDCs), every five years. These NDCs outline specific emission reduction measures and resilience-building strategies tailored to each country's circumstances [9; 10]. Figure 2 offers a timeline showing international treaties based on the will of global political powers to address climate change. The objectives and deadlines imposed differ from one state to another, mirroring the variations in international agreements. Generally, countries with developing economies are afforded a wider and less stringent timeframe. Table 1 illustrates the decarbonization objectives of some of the most emitting states. Figure 2: Timeline of major global climate treaties. Self-elaboration based on [8; 9; 10]. A particular importance is given to the necessity of decarbonizing the world's electricity system. This is critical for addressing climate change and ensuring access to clean and affordable electricity for everyone, in line with SDG 7. Achieving this goal requires a significant increase in the use of renewable energy sources (RESs) in electricity grids. Responding to the urgent need for rapid decarbonization across the global economy, a coalition of energy buyers, suppliers, governments, system operators, solution providers, investors, and other stakeholders has come together to promote 24/7 Carbon-free Energy (CFE). This approach ensures that every kilowatt-hour of electricity consumed is matched by carbon-free sources every hour of every day [19]. In this perspective, in the Climate Ambition Summit convened by the UN Secretary-General in 2023, a Climate Action Acceleration Agenda (CAAA) was presented which aimed to accelerate the set of actions requested by various leaders for a drastic reduction in GHG emissions, trying to bring forward the net-zero deadlines to 2040 for developed countries and 2050 for emerging countries, and to present energy transition plans with tangible actions by 2035 for developed countries and 2040 for developing countries. Also, the Organization for Economic Cooperation and Development (OECD) countries must accomplish the coal phase out by 2030, while the rest of the world should achieve it by 2040. The CAAA, above all, calls for accelerating the decarbonization of sectors such as shipping, aviation, and industry, in particular the steel, cement, and aluminum industries while pressing to reallocate fossil fuel subsidies toward renewable energy initiatives. This shift is vital for fostering the growth of sustainable energy sources, which can play a significant role in meeting net-zero targets [10; 20]. In particular, electricity is projected to become the dominant energy carrier, potentially accounting for over 50% of TFEC by 2050, driven by the enhanced deployment of RESs, improved energy efficiency, and further electrification across various sectors. In the buildings sector, heating and cooling technologies, particularly HPs, are promising for further electrification based on carbon-free electricity. In 2022, global HP installations grew by 11%, with a notable 38% increase in Europe.