Wet Bulb at 33 C — Human Hothouse Kills Nearly 800 in Pakistan

Human-forced warming of the global climate system is pushing sea surface temperatures in some areas to a maximum of 33 C. Extreme ocean warming that is increasing the amount of latent heat the atmosphere can deliver to human bodies during heatwaves. And near a 33 C sea surface hot zone, the past few days have witnessed extreme heat and related tragic mass casualties in Sindh, Pakistan.

*    *    *    *   *

For Pakistan, the heat and humidity has been deadly. Temperatures over Southeastern Pakistan hit 100 to 113 Fahrenheit (40 to 45 degrees Celsius) during recent days. Night time lows dipped only into the 80s and 90s (30s Celsius). Relative humidity throughout this period has remained above a brutal 50% even during the hottest hours of the day.

Wet bulb temperatures (the wet-bulb temperature is the temperature air has if it is cooled to saturation — 100% relative humidity — by evaporation) climbed into a dangerous range of 30 to 33 degrees Celsius. This greatly reduced the ability of evaporation at skin level to cool the bodies of human beings exposed to such oppressive temperatures. As a result, people working outdoors, the elderly, or those without access to climate-controlled environments fell under severe risk of heat related injuries.

The Hospital Morgue is Overflowing

According to reports from Al Jazzera, thousands of heat injuries and hundreds of deaths have occurred across the region since Saturday. Karachi’s largest hospital — Jinnah Postgraduate Medical Centre (JPMC) — has been flooded with over 5,000 patients suffering from heat injuries since the weekend. At some points, the hospital was receiving one heat injury patient per minute — a pace that nearly overwhelmed the facility. By earlier today, more than 380 of those patients had died.

Dr Seemin Jamali, a senior official at JPMC noted to Al Jazeera:

“The mortuary is overflowing, they are piling bodies one on top of the other. We are doing everything that is humanly possible here. Until [Tuesday] night, it was unbelievable. We were getting patients coming into the emergency ward every minute.”

Across Sindh, Pakistan the story was much the same with the total official heat death toll now standing at 775 and climbing as calls were raised for more government support for people impacted by the worst heat wave to hit Pakistan in at least 15 years.

Killing Heat and Unprecedented Rains

This extreme and deadly heat is a feature of a boundary zone between a hot, high-pressure air mass over the Persian Gulf region abutting against a very moist and El Nino-intensified monsoonal system over India. The result is a combination of high heat and high humidity — factors that, together, are very hard on the human body (wet bulb temperatures above 30 C are considered dangerous, while a blanket measure of 35 C [never reached yet on Earth] is considered rapidly deadly even in the shade).

During late May and early June, similar conditions resulted in hundreds of heat related deaths in India. When the heat finally abated, the subsequent influx of monsoonal moisture set off torrential downpours. In some places, rates of rainfall exceeded typical June monsoonal accumulations by nearly 50 percent with Mumbai already having received 32 inches of rainfall (normal June rainfall is 23 inches). With Mumbai showing daily rainfall accumulations of 1-3 inches, it is possible that June totals could be double that of a typical year.

A Ramping Oceanic Heat/Moisture Pump — Feature of a Record Warm World

The high heat, high humidity and related extreme rainfall events are all features of a warming world. At issue, primarily, is the impact of human forced global warming on the ocean system and how this heating then impacts the atmosphere — making it harder for humans to remain alive outdoors during the most extreme heating events even as it pushes a tendency for more and more extreme droughts and deluges.

This warming related heat and moisture flux is most visible out in the Pacific, where record global atmospheric and ocean heat is pushing maximum sea surface temperatures into the lower 30s (typically between 30 and 31 degrees Celsius). These high sea surface temperatures in a record warm world are now dumping an extreme amount of moisture into the atmosphere through an El Nino amplified evaporation rate. A subsequent amplification of the equatorial storm track due to extreme moisture loading has already seen extraordinary record rainfall events in places as widespread as India, China and the Central U.S.


(Sea surface temperatures climb to near 33 C in the Ocean region near Pakistan — supporting wet bulb temperatures [high heat and high humidity] that generate a heightened risk of heat injury and death. Image source: Earth Nullschool.)

Maximum global sea surface temperature is a good proxy measure for how much moisture the atmosphere can hold, a measure that also likely determines the maximum wet bulb temperature (implied latent heat) at any given point on the globe. And particularly, near Pakistan, we find ocean surface temperature readings in the range of 30 to 33 C running through the coastal zone of the Indian Ocean and on into the Persian Gulf. Readings that increased the amount of moisture the atmosphere could hold at high temperature, increased relative humidity readings as temperatures entered the 100s Fahrenheit (40s C), and forced wet bulb temperatures into deadly ranges which in turn reduced the ability of the human body to cool by evaporation at skin level.

This is how human-forced global warming kills with direct heat — by basically increasing latent heat to the point that evaporation can no longer cool the human body to a natural maintenance temperature of 98.6 (F) or 37 (C). And once wet bulb temperatures start hitting 35 C, then the heat casualty potential really starts to get bad — essentially rendering heat wave regions temporarily uninhabitable for human life outdoors. With maximum sea surface temperatures now running near 33 C, we’re probably just within about 2 C of hitting that deadly boundary.

The Pakistan and Indian heat deaths this year, though extraordinarily tragic and probably preventable without current level of human forced warming of the atmosphere, serve as a warning. Keep warming the globe through fossil fuel emissions and there are many far, far worse heatwaves to come.


Pakistan Heatwave Death Toll Edges Toward 800

Pakistan Heatwave Death Tool Rises to 750

Heavy Rain Soaks India as Monsoon Advances

Flash Floods Pelt China

Earth Nullschool

An Adaptability Limit To Climate Change Due to Heat Stress

Hat Tip to Colorado Bob

Leave a comment


  1. james cole

     /  June 24, 2015

    That’s a brilliant post Robert! The world we live on is 2/3 ocean, and it’s taking up of record heat can only mean disaster is building. Water that warm? It almost beggars belief!

    • For the Fahrenheit-oriented, a 33 C sea surface temperature is 91.4 F. And James is right. That’s ridiculously hot water when it comes to oceans.

      • Mark from New England

         /  June 24, 2015

        I can’t imagine ocean waters that warm. Probably doesn’t support much in the way of marine life either.

    • Yvan Dutil

       /  June 24, 2015

      At that point it is hard to find an appropriate superlative! This situation is a preview of what has been predicted by Sherwood & Huber (2010)

      • Thanks for the reference, Yvan. I’ve added it to the links above.

      • Yvan Dutil

         /  June 24, 2015

        A more recent paper on the same topic. There is a map for future climate in India. Scenarios are less extreme than the PNAS paper, but probably more realistic, hence much scarier.

      • Griffin

         /  June 24, 2015

        Interesting that the paper was approved in 2010. In the opening paragraph – Heat stress…never exceeds 31C.
        Things are getting much worse, and faster, than so many ever expected.

        • Worth noting that my wet bulb calculation does not include atmospheric pressure — which is one factor that could swing the numbers a bit. But it does look like the primary limiter for maximum wet bulb temperature is related global maximum sea surface temperature. There seems to be a rough, but pretty direct correlation between the two.

    • UPDATE: death toll has now hit 1150…

  2. climatehawk1

     /  June 24, 2015

    Tweet scheduled.

  3. Spike

     /  June 24, 2015

    For those who missed it, the Guardian covered heat and human health very well recently

  4. Oceans at 90 to 96 F (32 to 35 C) are also potent sources of hurricane fuel. I don’t think Pakistan has ever seen many such storms unlike Bangladesh and Burma. I suppose they should beware of them, especially strong ones, now.

  5. Spike

     /  June 24, 2015

    I was reminded of the impact of heat extremes on conflict between humans also – not insignificant as a risk in South Asia and the Middle East

  6. Hi Robert,  2000 people and counting, Rob From: robertscribbler To: Sent: Wednesday, 24 June 2015, 19:31 Subject: [New post] Wet Bulb at 33 C — Human Hothouse Kills Nearly 800 in Pakistan | robertscribbler posted: “Human-forced warming of the global climate system is pushing sea surface temperatures in some areas to a maximum of 33 C. Extreme ocean warming that is increasing the amount of latent heat the atmosphere can deliver to human bodies during heatwaves. And…

  7. Griffin

     /  June 24, 2015

    Incredible post Robert. You are (again) right on with another tremendous threat to humans.

  8. – Remember that heat and air pollution make for a lethal environment.

    Air Quality Impacts Associated with Climate Change

    Air pollution levels are directly influenced by changes in weather, such as heat waves. Changes in weather that might result from climate change, such as warmer temperatures and more frequent episodes of stagnant air, therefore, also have the potential to affect air pollution. In addition, increases in heat-related mortality and morbidity are expected due to warmer temperatures.

  9. – If one should find they have trouble with cognitive functions…
    Me thinks we have been destroying reasoning brain cells, etc for quite a while with out arsenal of FF pollutants. Maybe this helps explain our current existential dilemma.
    Of course, we have also crowded out most breathable air in the atmosphere and replaced it with toxic gases and particulate.

    “We’re getting hammered right now,” Cross says, shouting over the hum of the engines. He’s taken his gloves off to manipulate the display panel on his pollution monitor. The acrid smell of diesel is unmistakable. “Anytime you can smell it, you are in a regime that is very polluted,” he says. “In many ways your nose is a better mass spectrometer than any device on the market.”

    … trucks’ engines, combined with their inefficient combustion in cold weather, means that the air reaching us is replete with fine and ultrafine particles—specks of waste at least 36 times finer than a grain of sand, often riddled with toxic combinations of sulfate, nitrate and ammonium ions, hydrocarbons, and heavy metals. Though we have long known that these tiny particles cause and exacerbate respiratory problems—like asthma and infections and cancers of the lungs—they are also suspected to contribute to a diverse range of disorders, from heart disease to obesity. And now cutting-edge research suggests that these particles play a role in some of humanity’s most terrifying and mysterious illnesses: degenerative brain diseases.

    • Panel of doctors give a warming Earth a physical and say kick the coal habit immediately

      WASHINGTON (AP) — Some top international doctors and public health experts have issued an urgent prescription for a feverish planet Earth: Get off coal as soon as possible.

      Substituting cleaner energy worldwide for coal will reduce air pollution and give Earth a better chance at avoiding dangerous climate change, recommended a global health commission organized by the prestigious British medical journal Lancet. The panel said hundreds of thousands of lives each year are at stake and global warming “threatens to undermine the last half century of gains in development and global health.”

      It’s like a cigarette smoker with lung problems: Doctors can treat the disease, but the first thing that has to be done is to get the patient to stop smoking, or in this case get off coal in the next five years, commission officials said in interviews.

      “The prescription for patient Earth is that we’ve got a limited amount of time to fix things,” said commission co-chairman Dr. Anthony Costello, a pediatrician and director of the Global Health Institute at the University College of London. “We’ve got a real challenge particularly with carbon pollution.”

    • All that mercury-laden coal dust… It’s really scary to think about. All the crap we are putting into our bodies every day just by burning fossil fuel. Fuels that we could just as readily say no to now with wind and solar prices so low. It really is a shame that we’re dragging our feet on getting rid of the big emitters. We’d be saving lives across the board. From health to climate it’s a win all around.

  10. Tsar Nicholas

     /  June 25, 2015

    There’s a sting in the tail when it comes to cleaning up the air. The current pollution – particulates,aerosols and so on, are masking the warming to some extent. So cleaner air will mean higher temperatures. we are damned if we do and damned if we don’t!

    • I think the way you say this is a mischaracterization.

      The warming currently masked by the aerosol fraction (particulate pollution) is already locked in. At this point, we have about 0.8 Watts per meter squared in that fraction or about 0.3 to 0.5 C worth of warming this Century. On the other hand, continuing to burn fossil fuels results in 2-8 C worth of additional warming on top of the aerosol masked fraction this Century. And that warming is preventable warming, where the aerosol fraction warming is not. So it’s not a question of damned if you do, damned if you don’t. It’s more an issue of — we’re not really aware how bad out current situation is because some of the warming we’ve already set off has been masked. That’s the Faustian Bargain — easier now, harder later, but really deadly if you don’t pay up as soon as possible.

      So this proper characterization is this — the pollution would fall out eventually (in the short term due to responsible action on the part of civilizations or in the longer term due to fossil energy depletion) and the masked warming is already locked in. It’s not something you get rid of by continuing to burn fossil fuels. And fossil fuel burning just makes the larger problem worse, by increasing the overall warming.

      It’s kind of like the case of a drug addict who’s addicted to something on the scale of heroine. If the drug addict quits, there’s withdrawal to deal with. And as long as the addict keeps using the drug, there will be the issue of withdrawal if the user stops. But if the drug addict doesn’t quit, the ongoing drug use would end up resulting in early death. Far better to quit, and far better to quit sooner rather than later.

      The real thing to highlight here is that because the situation is already worse than what we now observe, then we’d really better get our butts in gear.

      Similar language of defeat is rife today throughout the media. On WTOP this morning, I hear the news announcer praising increased gasoline use and then reading a report about how markets are up as a result. There’s still this insane perception in the media and the markets, the worst kind of herd mentality, that buying this stuff and burning it is somehow good news for the future. But it’s just a fleeting market buzz off what amounts to economic junk. And the storms and droughts and mass migration and increasing stress to crops and sea level rise triggering real estate busts and losses of whole fisheries and the risk of resource conflict all gather as these fossil fuel burning cheer leaders sing their praises for each additional gallon guzzled, or, on the other hand, make you fear an entirely necessary cessation.

  1. The Hothouse Yet Worsens — Japan Meteorological Agency Shows June of 2015 Tops Out a Century of Heating | robertscribbler
  2. Glacial Outburst Flood — Human Hothouse Displaces Hundreds in Tajikistan | robertscribbler
  3. Killing Heat — It Felt Like 165 Degrees in Iran Today | robertscribbler
  4. Japan in Hot Water — Longest Heatwave on Record for Tokyo, Tens of Thousands Hospitalized | robertscribbler
  5. Hothouse Mass Casualties Strike Egypt, Heatwave Continues to Hospitalize Thousands in Japan | robertscribbler
  6. Dangerous Heat Sets Sights on Southern United States | robertscribbler

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