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Can Humanity Handle the Heat?
By Kristie L. Ebi, Rachel Kyte, Rushad Nanavatty and Carlo Ratti

The Big Question is a regular feature in which Project Syndicate commentators concisely address a timely topic. Recent record temperatures of more than 40º Celsius in the United Kingdom, and outbreaks of wildfires in several European countries, again highlight the challenges posed by ongoing climate change. The need for robust, scalable systems to counter extreme heat is clear – but developing and implementing them will require political will as well as technological innovation. In this Big Question, we ask Michael R. Bloomberg, Kristie L. Ebi, Rachel Kyte, Rushad Nanavatty, and Carlo Ratti what the world can do to stay cool.


The most important thing we can do to protect people from increasingly dangerous heat waves is to turn up the heat on elected leaders who put the interests of fossil-fuel companies above public health and safety. As more people feel the effects of climate change in their own lives, more are stepping up and demanding that their leaders take action – or be voted out of office.

That’s not happening nearly fast enough, including in the United States. But the good news is that mayors and local leaders aren’t waiting for national governments. Mayors around the world are taking bold action to reduce climate pollution, including steps that help people beat the heat today.

For example, planting more trees and painting roofs white help to cool city streets and buildings, while also reducing carbon footprints. In New York City, my administration launched an initiative to plant one million trees, which helped cool neighborhoods and make heat waves less deadly. Bloomberg Philanthropies is helping many cities around the world take similar steps, while also ensuring that mayors have the tools to address the leading cause of worsening heat waves: consumption of fossil fuels.

Local rules to improve energy efficiency help buildings stay cooler in the summer, which leads to lower greenhouse-gas (GHG) emissions and lower costs. More solar and wind energy makes the electricity grid cleaner and more reliable. Expanded public transit keeps polluting cars off the road.

Extreme heat is an urgent public-health issue, and an equity issue, too: Heat waves exact the biggest toll in developing countries. And in wealthier countries, lower-income communities often have fewer parks and trees, and less access to air conditioning. It’s a serious economic issue as well, because heat waves kill crops, reduce productivity, and damage infrastructure.

So, we have every incentive to act, starting with dramatically increasing investment in clean energy. The longer we wait, the harder it will be for humanity to handle the heat.

Acclimatization, creativity, and technology and infrastructure innovation enable humans to inhabit a wide range of sometimes hostile environments. And humans and cities alike have adapted over time – including by migration when necessary – as regions became more (or less) desirable.

But these adjustments occurred over decades. Climate change is placing increasing demands on the pace of adaptation as heat waves increase in frequency, intensity, and duration. Multiple simultaneous extreme heat waves across continents in the northern hemisphere this summer highlight the challenges that additional climate change is expected to bring to individuals, communities, and regions.

Exposure to high ambient temperatures can harm human health and well-being, cause preventable hospitalizations and deaths, reduce worker productivity, and affect upstream factors influencing health such as food and water safety and security. Together, these effects compound existing inequities and can affect a location’s livability. People over the age of 65, pregnant women, those with chronic medical conditions or who are taking a range of prescription drugs, outdoor workers, and those living in poor and marginalized communities are particularly vulnerable to high temperatures.

Preventive measures include developing heat action plans, such as investment in longer-term infrastructure for a hotter future. Building warning and response systems for heat waves is also essential, in order to provide vulnerable populations and regions with information, tools, and access to needed services to keep them safe from the worst effects of extreme temperatures.

But will these steps be sufficient in a world with hotter and more humid summers, more intense heat waves, and aging populations? The northern hemisphere summer of 2022 is projected to be cooler than summers later this century in a scenario of high GHG emissions. Being prepared for this future requires an all-of-society effort. That includes developing new building materials and more efficient approaches to cooling buildings and inhabitants, increasing public awareness of the health risks of heat waves, enhancing collaboration across services, and more.

Urgent and immediate investments are needed, focusing on people and regions most at risk, to ensure the livability of our communities in a hotter future.

Yes, if we adapt now and learn the first lesson of resilience: We are safe only if everyone is. Extreme heat underscores how those most vulnerable to it are on the front line of climate change. In cities, leafier districts are several degrees cooler than the concrete jungles where many workers live. Across more than 50 countries that are at the highest risk from extreme heat, more than 1.2 billion people don’t have access to cooling.

So, how to handle the heat? First, we must act urgently to reduce the emissions that drive extreme heat. That includes fixing air conditioning, because we are warming the planet to cool ourselves. Air conditioning accounts for 10% of energy demand and is on the rise, with the number of AC units globally expected to increase from 1.6 billion today to 5.6 billion in 2050. This demand must be met by hyper-efficient systems and appliances that are free from polluting refrigerants that accelerate global warming.

But there is more to cooling than AC. Cooling means redesign – from designing out waste heat from chillers to designing in green infrastructure to mitigate urban heat islands. Cool requires new planning, architecture, and building materials.

Second, we need to communicate the dangers directly. Let’s name extreme-heat events like we do hurricanes (people pay more attention), publish wet-bulb numbers (temperature readings based on a combined measure of heat and humidity) like we would high pollen counts, map communities to know who is at risk, and provide advice.

Third, extreme heat affects productivity, and leaders need to understand and track it better. Children learn less in suffocating classrooms, firms slow or cancel hiring, and roads and rails buckle, bringing commerce to a halt.
Lastly, we must unleash the power of city leaders. From Boston to Freetown and Athens to Medellín, mayors are leading the way with heat czars, tree equity plans, cool roofs, cooling centers, and better public information systems.

Yes, we can. Or at least some of us can for now – if we do things differently.

Three things are worth bearing in mind. First, “humanity” is not a monolith; different people will be affected by higher temperatures in vastly different ways. If you are rich or live in a rich country, you probably have an air conditioner, can buy one, or have access to a cool public space such as a park or an air-conditioned mall. If you get heat stroke, good emergency services can whisk you away to well-resourced care. But if you are poor or live in a poor country, you probably can’t afford AC and probably work outdoors or in your home. Poverty may have already compromised your health, and quality care is hard to come by.

Second, heat risk is non-linear. A “wet bulb” temperature of 35°C is not fractionally worse than one of 30°C, but it is the difference between life and death. And as the world continues to warm, we are much more likely to encounter those conditions in Jakarta, Lagos, and Delhi than we are in London, Paris, or New York.

Third, we have the solutions. But we need to act urgently to embed them in our built environment – especially in hot, fast-growing cities in Africa and Asia. This means making space for more greenery and water in urban areas. It means making buildings more efficient so that they keep cool air in and heat out. It means developing more efficient AC technology (not least because inefficient equipment is a major contributor to global warming). And it means having road and roof surfaces that reflect heat rather than absorb it.

Deploying these solutions will take concentrated effort and money. But philanthropic donors that care about climate justice – like the IKEA Foundation, which recently made a $25 million grant to the Clean Cooling Collaborative – can make a difference. Likewise, non-profit organizations, businesses, and governments are starting to mobilize, including via the Cool Coalition.

So, there is still hope. But the clock is ticking – and the mercury is rising.


Heat waves have been sweeping across Europe over the past month, breaking one temperature record after another. But behind this pattern might lie an even more troubling truth: Climate models that have been used to predict the future impact of GHGs may be underestimating the severity of global warming. What might humanity’s options be if we are overshooting the current target of limiting global warming to 1.5º C above pre-industrial levels?

While reducing GHG emissions should remain the primary approach to tackling climate change, we should start exploring alternatives – as the Climate Overshoot Commission, among others, has recently argued. For example, solar radiation modification systems would partly reflect sunlight away from the planet to limit temperature increases. It has been estimated that reducing incoming solar radiation by 1.8% would counter today’s global warming.

Different methods of solar radiation modification have been proposed – from the brightening of clouds over the oceans to the introduction of aerosols into the upper atmosphere. Together with a transdisciplinary pool of colleagues at MIT, we have started working on a space-based alternative. The idea is inspired by the work of Roger Angel, a NASA astronomer who in 2006 outlined the concept of a giant umbrella placed at the Lagrange point between the Earth and the sun to reduce the amount of incoming radiation.

How could such a solution be implemented? Bubbles that we have tested in outer-space conditions at our labs could be one of the most lightweight and efficient thin-film structures for this purpose. Their fabrication directly at the Lagrange point might be an effective way to produce a raft for reflecting solar radiation. Such a solution would also be fully reversible, as the bubbles could easily be popped and would generate a minimal amount of space waste.

Beyond the development of a working technology, many other questions remain open – first and foremost those related to project governance. But humanity needs to start working on backup plans in case climate change spins out of control.

(Authors Michael R. Bloomberg is the United Nations Secretary-General’s Special Envoy on Climate Ambition and Solutions, Kristie L. Ebi is Professor of Global Health and Environmental and Occupational Health Sciences at the University of Washington, Rachel Kyte, a former UN climate envoy, is Dean of the Fletcher School at Tufts University, Rushad Nanavatty is Managing Director of the Urban Transformation program at RMI and Carlo Ratti, Director of the Senseable City Lab at MIT, is Co-Founder of the international design and innovation office Carlo Ratti Associati.)
For Indian tourists travelling by land:- 72 hours (-ve) C-19 report, CCMC form and Antigen Test at entry point

For Indian tourists travelling by land:- 72 hours (-ve) C-19 report, CCMC form and Antigen Test at entry point

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