Western Heat Predicted to Move East

The extreme heat that is helping to fan severe western wildfires from California to Alaska is predicted to move eastward over the coming days. This shift is expected to set off high temperatures in the 90s and 100s from the Gulf Coast all the way to the Great Lakes and into the Northeast. Heat Index values, meanwhile, are predicted to spike into the 100s and 110s from the Mississippi Valley north and eastward.

(Much warmer than normal temperatures spread from west to east across the U.S.)

These much warmer than normal temperatures and potentially dangerous heat index values occur in a context of larger national and global warming. May of 2018 was the hottest on record according to NOAA. The U.S. presently sits between two warmer to much warmer than normal ocean zones. And overall global temperatures have been rising since the 1900s, with a more rapid up-ramp occurring since the late 1990s.

For the Central and Eastern U.S., warmer than normal oceans are also spiking atmospheric moisture levels through increased rates of evaporation. These higher moisture levels will be contributing to predicted heat indexes where large regions are expected to experience temperatures that feel like the 100s or 110s (see image below).

(Heat index values are predicted to rise to between 40 and 45 C for large parts of the Central and Eastern U.S. The 44 C predicted heat index for parts of Western New York on July 1 corresponds to a 111 F ‘feels like’ condition for this Northeastern region. Such high heat index values present a heightened risk of heat injury due to long term exposure. Image source: Earth Nullschool.)

Combined high heat and humidity increase the risk of heat injury due to exposure. And rising heat indexes and wet bulb temperatures are just one of the many potentially harmful aspects of human caused climate change.

From Inverse:

In the future, parts of the world will become so hot and humid that healthy adults sitting in the shade will die within a matter of hours. It’s hard to imagine, and yet that’s where Earth’s climate is headed, perhaps sooner than expected.

But while many recent studies have rightly focused on physical human limits under high wet bulb temperature risks for parts of South Asia and the Middle East, the Central to Eastern U.S. is also a region of concern. Climate risks to this region of the U.S. are due to both high predicted temperatures and high moisture levels from increasingly warm Gulf and Atlantic Ocean surfaces. The result is that heat capable of resulting in rapid heat injury or even loss of life, with wet bulb temperatures above 35 C, is possible by mid-to-late Century under high fossil fuel burning scenarios.

(At 10 C global warming, large regions of the world are regularly predicted to experience temperatures above 35 C Wet Bulb readings — or a level at which the human body is not naturally capable of cooling itself. Of course, such dangerous Wet Bulb readings are possible under still lower levels of global warming. Note that the Central to Eastern U.S. is one of the indicated hot spots from this recent paper.)

Though the Eastern U.S. is not yet facing extreme wet bulb readings of this kind, temperatures and humidity levels are presently on the rise. So the predicted heat wave is still expected to pack a punch. And perhaps a bit more than we’re used to.

We’re looking at a predicted extended period of significant above normal temperatures and high humidity over the coming days. So the public should stay tuned to local media for heat advisories issued by the National Weather Service (see heat safety tips here) and do what they can to keep cool by drinking water frequently and by spending less time exposed to blazing temperatures and sweltering humidity.

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Killing Heat — It Felt Like 165 Degrees in Iran Today

In Iran it was 115 degrees Fahrenheit today (46 C). Add in humidity and the heat index was a stunning 165 F (74 C). But what they really should be concerned about is the wet bulb reading

A Limit to Human Heat Endurance

Thirty five degrees Celsius. According to recent research, it’s the wet bulb temperature at which the human body is rendered physically unable to cool itself in the shade. At which evaporation not longer cools the skin. A temperature that results in hyperthermia, heat exhaustion and heat stroke — even when sitting still and out of direct sunlight over the course of about 1-3 hours. Basically, it’s the physical limits of human heat endurance.

The primary factors involved in determining wet bulb temperature are atmospheric temperature and humidity. The temperature of an air parcel cooled to saturation (100 percent humidity). Basically, it’s the coolest temperature human skin is able to achieve by sweating.

One of the reasons why high heat and high humidity seem so oppressive is the fact that it interferes with water evaporating from your skin keeping your body at its natural temperature (98.6 F). High heat + high humidity means less cooling at skin level, which can result in a pretty rapid over-heating. We’ve all experienced it, that sense of stifling on a hot, muggy day. And there’s a bone-deep reason why it feels so bad. Hit a too-high intensity and it’s a killer.

Persian Gulf Heatwave

(An oppressive heat dome high pressure system settles in over the Persian Gulf. Image source: Ryan Maue.)

At 47 percent relative humidity and 115 degrees Fahrenheit, it felt like 165 degrees (F) today in Bandar Mahshahr, Iran. That’s a wet bulb temperature of 34.7 C. A temperature near the edge of human limits and the second highest heat index value ever recorded in any official or unofficial measure (the highest unofficial measure was 178 F). It’s the kind of heat that is, quite frankly, deadly.

Heat Dome Settles Over Persian Gulf, Sea Surface Temperatures Spike

Bandar Mahshahr sits at the Northern end of the Persian Gulf. A region of water that features some of the highest sea surface temperatures on Earth. Over the past week, an oppressive heat dome high pressure system began to settle over the region. Air temperatures around the Gulf hit well above 110 F in many locations. In Baghdad, they soared to 122 degrees F (50 C). Yesterday and today, the sea surface temperatures also sweltered — ranging as high as 34.6 C (94 degrees F).

Since ocean surface temperatures produce latent heat and determine the maximum moisture loading of the Earth atmosphere, maximum sea surface temperature is a good basic yardstick to determine if surface wet bulb temperatures are capable of hitting or exceeding the human survivability threshold at 35 C. And what we are seeing is that the near Persian Gulf region is steadily entering this dangerous range.

image

(Sweltering sea surface temperatures like those now visible in the Persian Gulf can support heatwaves that the human body did not evolve to endure. Image source: Earth Nullschool.)

As the heat dome continues to settle in over the next week, there is increasing risk to the people living in the Persian Gulf region. Some have access to cooled shelters, life saving ice and water. But many do not. At particular risk are the over 3 million Iraqis displaced by the violent conflict wracking that fractured state. Chronic electricity and water cuts throughout the region also lends to the overall vulnerability. It’s a current crisis. But it is one that occurs in an overall worsening context.

As the world’s oceans continue to be warmed by heat trapped through human greenhouse gas emissions,  sea surface temperature thresholds will be driven inexorably higher. The potential moisture content in the near surface atmosphere will rise and so will temperatures. This will increasingly generate heatwaves which the human body simply does not have the physical capacity to endure. Overall, this is one of the reasons we see more mass casualty events as a result of heatwaves — like the events occurring this year in Pakistan and India. It’s a case of pushing the atmospheric heat and moisture loading beyond human survivability thresholds. And we’re steadily doing that now. Let’s hope that this week’s Persian Gulf heatwave doesn’t add another hothouse mass casualty event to the growing list.

Links:

Physical Limits to Adaptation

Middle East Broils Under Extreme Heatwave

Iran City Hits Suffocating Heat Index

Earth Nullschool

Pakistan Heatwave Mass Casualty Event

India Heatwave Mass Casualty Event

Hat Tip to Robert in New Orleans

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