In this special issue of Science, Cooling in a Warming World, three Perspectives and three Reviews highlight the wide array of new and improved technologies and solutions that aim to keep us and the materials we rely on cool, in our rapidly warming planet.
Record-breaking heatwaves and extreme temperature events are on the rise globally; however, their impact is becoming increasingly difficult to quantify. In the first Perspective in this special issue, Steven Sherwood discusses the difficulties associated with predicting and understanding the consequences of regional heat events. He emphasizes that climatic events approaching the limits of human tolerance are already occurring, as highlighted in a spring 2020 Science Advances paper that showed extreme humidity events emerging ahead of projections, for example. According to Sherwood, the world's poor are the most vulnerable to extreme temperatures, highlighting the need for low-cost adaptations and technologies to counter the rising heat. In a second Perspective, Po-Chun Hsu and Xiuqiang Li address how global warming has created a demand for innovative new textiles that help cool those who wear them. "Rather than engineering the existing clothing materials," they say, "the key to radiative cooling is to re-invent the material so that it is transparent in mid-infrared, allowing the thermal radiation from the hot human skin to bypass the textile and directly reach the ambience." A final Perspective by Amy Fleischer highlights the growing demand for cooling at data centers, where vast amounts of information are stored and supported , and the majority of the total energy required to keep them online is used for cooling. Fleisher describes the improvements and novel approaches used to address rising energy demands for data center cooling that could be applied without increasing cost and emissions.
In a Review, Mark McLinden and colleagues offer an overview of vapor-compression refrigeration - perhaps the most widely used cooling technology on Earth. Most refrigeration and air conditioning systems are based on vapor compression. However, they lack efficiency and often contain harmful refrigerants, which can further contribute to atmospheric greenhouse gasses. McLinden et al. discuss how the high global warming potential of current vapor-compression cooling equipment has led to an effort to improve the technology and develop new and more environmentally friendly alternative refrigerants. In a second Review, Xavier Moya and Neil Mathur provide an overview of using caloric materials for cooling and heating. Caloric materials transport heat as they are electrically, magnetically or mechanically manipulated. According to Moya and Mathur, magnetocaloric, electrocaloric and mechanocaloric materials have shown promise in prototype cooling devices that operate near room temperature. The final Review, by Xiaobo Yin and colleagues, describes the use of passive radiative cooling materials, which leverage an atmospheric window to release heat in the form of infrared radiation into the coldness of space. When deployed on rooftops, these systems can potentially cool buildings by a few degrees, even in the daytime and under direct sun.