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.

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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


Mangled Jet Stream Delivers Four Months Worth of Rain in One Week to Missouri; Central, Eastern US to Remain Under Severe Flood Threat

Mangled Jet Stream August 8

(Image source: California Regional Weather Service)

The Jet Stream over North America is a complete basket case. It is far less a river of air flowing between colder northern regions and warmer southern regions than it is a disassociated hodgepodge of cut off air flows. In the far north over a region of coastal Alaska and the Northwest Territory, an Arctic heat dome has formed and grown more prominent setting off temperatures ranging from the high 70s to high 80s as far north as the shores of the Arctic Ocean. This system, which has already lasted for nearly a week over this region is expected to persist until at least mid August as it ever so slowly drifts south and east. Over the west coast of the US, another cut off low sits almost motionless. Over a region between the Great Lakes and Hudson Bay a second upper level low meanders, drifting slowly west, if it moves at all. To the south, a large high pressure system also sits over the Gulf of Mexico. And from the east, a final low moves from east to west riding the tropical flow in toward Florida.

Between them all sits a stationary storm system that simply cannot move. And so it dumps rain day after day after day.

The Jet Stream is so weak over North America that these systems are essentially locked in place. And that means more persistent weather. In the case of Missouri and Tennessee, where these upper level systems are combining moisture flows from the southwest monsoons, the Pacific Ocean, from the Atlantic and from coastal and western Canada over a stalled frontal boundary, it means a great, daily dumping of rain.

NOAA water vapor August 8

(Image source: NOAA)

The net effect of these colliding and stagnate flows is a kind of storm sandwich that is focusing in on Missouri and Tennessee even as it spreads broader impacts over a twelve state region. You can clearly see these convergent and stationary systems in the water vapor image above provided by NOAA. Note the low pressure swirls off the US West Coast, in Canada, and off the US East Coast. You can also see numerous streams of moisture flowing from the Gulf of Mexico, from the monsoonal systems over Mexico and Texas, from the west coast low, and being pulled down through a still moderately active Jet Stream flow over western Canada. The swirl of whites and blues over the Central US represents an ocean of atmospheric moisture readying to dump yet more rain over Missouri, Tennessee and the central and eastern US.

Over the past week, satellite shots show persistent storms popping up again and again over the same region:

Aug 2 rains August 3 rains August 4 rains August 5 rains August 6 rains August 7 rains

(Extreme rainfall over Central US from August 2 through August 7. Image source: NASA/Lance-Modis)

What this series of satellite shots represents is a constant, six day heavy storm pattern. Adding in the NOAA water vapor image above, it appears that today makes for day seven. And looking at the forecast, it appears this system is now set to expand eastward even as it continues to dump rain over already hard-hit ares.

The results of this continuous dumping of moisture over the Central US has been nothing less than staggering. In eastern Missouri, in a region near Fort Leonard Wood, over 14 inches of rain has fallen during the past week. Richland in central Missouri has received a whopping 17 inches. This massive dumping of rain represents the delivery of four months worth of precipitation in just six days. Brandon, another Missouri town, received a total of 8 inches of rain within the 24 hour period from Wednesday to Thursday. A broader region stretching from Kansas to Missouri and Arkansas and on through Tennessee received between 3 and 17 inches of rain over the same one week period. And a still larger area encompassing Georgia, the Carolinas, Alabama and Kentucky also experienced abnormally heavy rainfall, washed out roads, and destroyed houses.

In the west, rivers which, in some cases were near record low levels, surged to new record highs. The east, which has endured far above average precipitation since mid spring, saw already swollen rivers leap their banks.

According to AccuWeather:

The Gasconde River at Jerome, Mo., set a record high level of 31.81 feet, breaking the old record of 31.34 feet set on Dec. 5, 1982. A near-record crest is forecast by National Weather Service hydrologists farther downstream on the river at Rich Fountain, Mo.

[Meanwhile,] the Maries River in Missouri crested just below record levels.

These very intense periods of rain set off flash flooding that inundated roads and destroyed at least 50 homes. Hundreds of homes were also inundated over a broader area with residents forced to flee to roof tops as water levels rapidly rose. The scenes of highways flooded, homes inundated, rivers reaching record or near record levels, and people being forced to flee from raging flood waters repeated again and again in a large swath from Kansas stretching eastward to the Carolinas. In total, more than 12 states have been seriously impacted.

ABC News last night, in the below video, aptly described the hardest-hit areas as turning into ‘a water world.’ The coverage shows storm shocked residents staring in awe at lakes forming in roadways, being rescued from the roofs of their homes, or being forced to rescue heavy equipment from flash floods. One beleaguered Georgia resident, after watching flood waters sweep his dog away, states: “I can’t live here no more, I’m through…”

However in depth and accurate, the above video misses the broader overall storm context of stalling Jet Stream flows, cut off upper level lows, and converging upper level moisture streams. ‘Stationary front’ is, therefore, a shallow and inadequate explanation of the patterns involved. The reporters would have done well to interview Stu Ostro and Dr. Jennifer Francis as individuals who could give this very extreme event a proper context as it relates to ongoing changes in the world’s climate to include meandering Jet Streams triggered by loss of northern hemisphere snow cover and sea ice, an amping up of the hydrological cycle due to increased rates of evaporation and rainfall under a regime of rising temperatures, and powerful, dense high pressure systems arising from a thickening atmosphere that just want to sit in place for longer and longer periods. All these emerging factors combine to increase the likelihood of extreme, persistent weather patterns like the ongoing series of storms now driving major US floods.

Unfortunately, the forecast calls for this weather pattern to continue to dump rain over an expanding area. For today and tomorrow, a stretch from the US Midwest to the east coast is under the gun for additional heavy rainfall and powerful, sudden storms through at least the next four days. These weather systems aren’t moving and the powerful flows of moisture converging over the central and eastern US are predicted to remain in place. So it is likely that flooding will continue to intensify over the coming days.


California Regional Weather Service




(Hat tip to Commenter Steve)

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