written 21 May 2023
published 28 May 2023
Humans are warm blooded, radiating at least 100 watts of heat, even at rest, which allows for faster metabolism, and a wider range of habitable environments. This advantage when temperatures are cool, becomes problematic as things heat up. Our biological reaction is to sweat, cooling the skin by evaporation. However, sweat can only evaporate if the air around it can absorb more water.
Relative humidity compares how much water is in the air to the maximum capacity at that temperature. A thermometer wrapped in a water-soaked cloth give "wet bulb temperature", the lowest temperature that can be reached by evaporation under current conditions. At 100 percent relative humidity, the wet-bulb temperature is equal to the air temperature, no water can evaporate, and cooling by sweating or evaporation is not possible.
Even heat-adapted people cannot carry out normal outdoor activities past a wet-bulb temperature of 90 °F, equivalent to a heat index 130 °F. Heat index is how hot it actually feels, with relative humidity factored in. The theoretical limit to human survival for more than a few hours in the shade, is a wet-bulb temperature of 95 °F, equivalent to a heat index of 160 °F.
Heatstroke results when a body overheats. Symptoms include: body temperature over 104° F, flushed skin, rapid breathing, racing heart rate, nausea, vomiting, fatigue, headache, agitation, irritability, slurred speech, confusion, delirium, seizures, unconsciousness, and death. This outcome is true for all warm-blooded creatures, including pets, livestock, and wildlife.
During the heat wave last summer, our deck in Ukiah hit 117° F. The humidity that day was 11 percent, giving a heat index of 113° F. If the humidity was doubled to 22 percent, the heat index would have been 127° F. Higher humidity changes a difficult day into a potential hazard. While Ukiah usually has relatively low humidity, other parts of the world are increasingly at risk.
During the heat wave last summer few people in California died, but the air conditioning load almost crashed the grid. This summer, there are early indications that the heat will be greater. The ocean has hit record levels of heat, and indications are an El Niño event is building, typically bringing more heat to Central America, the Middle East, the Indian subcontinent, Southeast Asia, and Australia.
Last month, Los Angeles issued a summer heat alert, helping people become aware of the danger, and establishing cooling centers. Canada is currently experiencing 88° F heat, 35° F about normal for this time of year, with over 90 fires now burning in Alberta, many out of control. Australia is feeling the impact with drought and heat on the rise. Spain hit 98° F last month, very early in the year for them, and all of Europe is concerned, since 15,000 people died of heat in the EU last summer.
There is still a portion of the population that doesn't believe the climate crisis is real, just as there are folks who think the Earth is flat. It is Republican dogma that the climate crisis is a "hoax" pushed by the "libs" to attack American energy independence. The climate doesn't care what we "think" is true, because it is part of our collective reality. Atmospheric carbon dioxide lasts a thousand years and we are adding more every year, so it will keep getting hotter. Life on Earth will survive, but human civilization, and perhaps humanity as a species, will not. If we want to leave a habitable planet for our children, we must stop adding more CO2, and begin removing the thousand billion tons we have already injected into the atmosphere as soon as possible.
Those who have been working toward that goal continually wonder what it will take for enough people to "get it", so that effective change can begin. What is still lacking is the sense of urgency, that we may already be "too late", that only a concerted effort will turn the tide. The optimist in me sees that change is beginning. Since the fires of 2017, attention has grown in this portion of the State. But the years slip by with business-as-usual still dominating.
In "Ministry For The Future", fiction by Kim Stanley Robinson, the turning point is a massive heat wave in India, that kills a million people in one week. This summer we may see such an event in reality. Will that do it?
