We’ve spent the last few weeks mapping the new climate reality: a 2°C world, collapsed ocean currents, a freezing Europe, a hothouse tropics. We’ve watched biodiversity unravel and soil degrade. We’ve tracked the Hormuz crisis and the market complacency that follows every retreating tide.
But here’s the question that matters most: what do we actually do about it?
This is the first of a new series within The Hothouse Chronicles. We’re calling it Tools of Survival. Each installment will examine the practical, tangible technologies and strategies that will define how we live, work, and thrive on a hotter planet.
Today: the cooling arsenal. From the shirt on your back to the greenhouse down the road, here’s what’s coming.
Part 1 – The Wet-Bulb Imperative: Why This Matters Now
Before we talk solutions, we need to understand the problem we’re solving for.
Wet-bulb temperature (WBT) is the metric that matters. Unlike dry-bulb temperature – the number your weather app gives you – wet-bulb accounts for both heat and humidity by measuring the lowest temperature an object can reach through evaporative cooling. It’s a direct measure of your body’s ability to dissipate heat through sweating.
When WBT exceeds 28°C, the risk of heat exhaustion increases significantly. At WBTs above 35°C for extended periods, human survival becomes extremely difficult, even for acclimatised individuals resting in the shade with unlimited access to water. And due to climate change, an increasing number of regions worldwide are experiencing WBTs exceeding 35°C.
This is not a future problem. This is happening now. And it’s why the cooling technologies we’re about to explore are moving from “nice to have” to “essential infrastructure.”
Part 2 – Personal Cooling: The First Line of Defence
The most immediate defence against extreme heat is the one you carry with you. Personal cooling systems have advanced dramatically in recent years, moving from bulky, impractical prototypes to lightweight, wearable technologies.
Thermoelectric-Hydrogel Hybrid Cooling
This is the breakthrough that has the scientific community talking.
Traditional hydrogel evaporative cooling – which works by absorbing heat as water evaporates from a gel – has a fundamental limitation: in hot, humid conditions, the gel’s surface temperature drops too low for effective evaporation. The cooling paradox: the more you need it, the less it works.
Researchers at the University of California, San Diego, have solved this problem by integrating thermoelectric devices (TEDs) with hydrogels. The TED actively pumps heat away from the skin while simultaneously heating the hydrogel to enhance evaporation.
The results are remarkable. The hybrid system can operate in temperatures up to 55°C and relative humidity up to 88%, with wet-bulb temperatures above 35°C, for over six hours. In testing at WBT ≈38°C – conditions that would be lethal without intervention – the system maintained skin temperature in the comfortable range of 33.8–35.8°C.
The flexible cooling garment, weighing 530 grams including a battery, can be worn under clothing and adapts dynamically to changing environmental conditions and metabolic heat loads. A PID temperature controller automatically adjusts the TED’s power when the environment changes, maintaining a stable skin temperature.
Passive Cooling Gels
Not everyone needs battery-powered active cooling. For many applications, passive cooling gels offer a simpler, more accessible solution.
MIT-spawned startup Eztia Materials has developed a water-based polymer gel that, when incorporated into fabric and worn next to the skin, can reduce skin temperature by up to 10°C. The gel absorbs body heat and dissipates it into the air, acting like “additional sweating capacity through a second skin”.
The cooling lasts six to eight hours, after which a short soak in water recharges the gel for reuse. The company produces inner singlets, arm sleeves, bandanas, and scarf-like wraps. In field tests at a Singapore construction site, workers wearing the cooling attire had skin temperatures 4°C lower than those without.
The economics are compelling: a singlet costs US$57, arm sleeves US$37, and a bandana US$25. Each garment lasts three to six months. With economies of scale, costs will fall further.
Part 3 – Active Cooling Clothing: When Passive Isn’t Enough
For workers in extreme environments – firefighters, military personnel, industrial workers – passive cooling isn’t enough. They need active cooling that can handle the worst conditions.
Water-Cooled Vests
Research dating back decades, and refined continuously, shows that water-cooled vests provide protection physiologically equivalent to removing the entire environmental heat stress, even at wet-bulb temperatures of 33.9°C. In testing with mineworkers at a wet-bulb temperature of 30°C, cooling clothing significantly reduced heart rate, rectal temperature, and weight loss.
A 2025 study evaluating commercially available cooling garments under hot and humid conditions (36°C, 65% relative humidity, WBGT 32°C) found significant body cooling effects across multiple products. Different cooling systems – air, liquid, and hybrid – each have their strengths. Research comparing air and liquid personal cooling found that both systems partially alleviated heat strain, with air systems offering slightly more effective cooling in some configurations.
The challenge with protective clothing is that it inherently traps heat. Clothing insulation and evaporative resistance hinder heat transfer, leading to increased heat strain. This is why active cooling systems are so critical for workers in high-risk environments. Modern body armour systems, for example, require careful modelling of wet-bulb globe temperature offsets to manage thermal strain.
Part 4 – Air Conditioning: The Big Question
Air conditioning is the elephant in the room. It’s the most effective cooling technology we have – and the most energy-intensive.
Portable Air Conditioners
Portable air conditioners face a fundamental challenge in high-humidity environments: the wet-bulb temperature represents the theoretical floor for evaporative cooling. In dry air, swamp coolers can drop indoor temperatures dramatically because the wet-bulb is much lower than the dry-bulb. In humid air, the wet-bulb is close to the dry-bulb, and evaporative cooling provides little relief.
This is why conventional air conditioners – which use refrigerant cycles rather than evaporation – are essential in humid climates. Research on portable air conditioners in high-humidity environments has focused on optimising condensate utilisation to improve energy efficiency. At 35°C dry-bulb and 85% relative humidity, optimised designs can achieve a 4.7% improvement in energy efficiency ratio.
The Energy Challenge
The fundamental problem with air conditioning is that it’s energy-intensive – and as the planet warms, demand for cooling will skyrocket. This is why the energy transition we’ve been tracking is so critical. Without cheap, abundant clean energy, air conditioning becomes a luxury only the wealthy can afford.
The solutions we’ve explored in previous Hothouse Chronicles installments – solar, wind, nuclear, SMRs, geothermal – are the foundation that makes widespread cooling possible. The cleaner the grid, the more cooling we can provide without making the problem worse.
Part 5 – Cooling Beverages: The Hydration Factor
What about the simplest cooling technology of all: a cold drink?
Research on cold fluid ingestion shows that it is an appropriate administrative control for mitigating increases in body heat content during moderate-intensity work-rest cycles in dry heat. Cold drinks can reduce body core temperature before exercise, though the effect is less pronounced during exercise.
The primary benefit of cold liquids is likely explained by their rehydration effects. When heat builds up, the body transports it away from vital organs to the skin surface, where it’s transferred to the environment through convection and radiation. Staying hydrated supports this process.
There’s also a fascinating counterintuitive finding: drinking a warm beverage can actually cool you down. Warm liquids trigger a sweat response, and when that sweat evaporates, it provides more cooling than the small amount of heat contained in the beverage. As one researcher put it, “a larger amount of sweat means more cooling, which more than counteracts the small amount of heat contained in a hot beverage relative to the entire body”.
That said, in extreme heat, cold drinks are generally more effective, and rehydration is non-negotiable. Alcohol, however, is a diuretic that reduces your ability to lose heat through sweating – not recommended in a heatwave.
Part 6 – Cooling Gels: Topical Relief
For immediate, localised cooling, topical gels offer a quick and accessible solution.
Cooling gels work by efficiently absorbing heat from the skin and dispersing it, creating an instant cooling effect. Hydrogel technology locks in moisture, ensuring prolonged and consistent cooling.
More advanced formulations are emerging. Cooling gels designed to combat heat stress, irritation, and photo-aging damage are now available, enriched with active ingredients that provide instant cooling relief while soothing the skin.
These products are not a substitute for systemic cooling – they won’t prevent core temperature rise in extreme conditions – but they provide valuable comfort and can help manage heat stress in moderate conditions.
Part 7 – Large-Scale Cooling: Orchards, Greenhouses, and Beyond
Personal cooling addresses individual survival. But what about the systems we depend on: our food, our livestock, our infrastructure?
Greenhouse and Agricultural Cooling
Greenhouses, by their nature, trap heat. The transparent walls allow solar radiation to penetrate for plant photosynthesis, but this also causes large quantities of heat to accumulate inside. Cooling these structures is essential for year-round production.
Research on greenhouse cooling has explored various approaches: desalinated groundwater and seawater systems that cool and dehumidify air in compact panels; novel cooling techniques that can reduce energy consumption compared with conventional greenhouses; and integrated systems that combine semi-transparent PV modules with smart climate control.
The goal is to create controlled-environment agriculture that can maintain optimal temperatures even in extreme heat – protecting crops and ensuring food security.
Magnetic Refrigeration
Magnetic refrigeration is an emerging technology with significant potential for large-scale cooling.
The newest version of magnetic refrigeration uses gadolinium, a rare-earth metal that gets hot when exposed to a magnetic field. Magnetic heating and cooling is expected to be more expensive to produce initially, but Ames Lab sources project energy savings will pay for the system in about five years.
European research projects like CoolMagEvo are exploring magnetic cooling systems using magnetocaloric alloys. The goal is to develop an alternative technology for cooling applications that is more energy-efficient and environmentally friendly than conventional refrigeration.
Part 8 – Conclusion: The Cooling Hierarchy
As we navigate the hothouse world, we need to think about cooling in layers, from the individual to the industrial.
Layer 1 – Personal Passive Cooling: Cooling gels, passive cooling fabrics, ultra-light clothing. These are the first line of defence. They’re cheap, accessible, and require no energy. They’re not enough for extreme conditions, but they make moderate heat survivable.
Layer 2 – Active Personal Cooling: Battery-powered cooling vests, thermoelectric-hydrogel hybrid clothing, water-cooled suits. These are essential for workers in extreme environments and for anyone who must operate in conditions that would otherwise be lethal. They’re more expensive and require energy, but they work where passive cooling fails.
Layer 3 – Environmental Cooling: Air conditioning, both portable and fixed, for buildings and vehicles. This is the most effective cooling technology we have – but also the most energy-intensive. It’s essential for hospitals, data centres, and vulnerable populations.
Layer 4 – Industrial and Agricultural Cooling: Cooling for greenhouses, orchards, barns, and industrial facilities. This protects our food supply and our economy. Emerging technologies like magnetic refrigeration offer the promise of more efficient large-scale cooling.
Each layer has its place. Each layer is becoming more important. And each layer depends on the foundation we’ve been tracking throughout The Hothouse Chronicles: clean, abundant, affordable energy.
Because in a hotter world, cooling is not a luxury. It’s infrastructure. It’s survival. And it’s the biggest growth opportunity of the century.
Next time on Tools of Survival: The coming revolution in precision fermentation and how it’s reshaping our food system.
Citations for this report
- Cell Reports Physical Science. (2025). Thermoelectrically elevated hydrogel evaporation for personal cooling under extreme heat. [13†L5-L6]
- University of California, San Diego. (2025). Hybrid TED-hydrogel cooling garment. [8†L4-L8]
- MIT Department of Materials Science and Engineering. (2025). Gel-based cooling wear. [11†L15-L18]
- Eztia Materials. (2025). HydraVolt cooling technology. [12†L6-L8]
- ScienceDirect. (2025). Portable air conditioner optimisation in high-humidity environments. [1†L11-L14]
- Journal of Applied Physiology. (2024). Cold beverage ingestion and heat exchange. [4†L12-L15]
- Ames Laboratory. (2025). Magnetic refrigeration projections. [5†L18-L19]
- CoolMagEvo project. (2025). Magnetic cooling systems research. [5†L50-L51]
- Occupational Health & Safety. (2022). PPE and heat burden. [6†L8-L10]