written 26 August 2019
published 1 September 2019
Some people deny that climate change is real, and others poke fun at efforts to deal with it. But a lot of people are becoming alarmed. This July the Earth was the hottest on record, and Europe in now experiencing it's third heat wave this summer. The last one set records, caused deaths, and disrupted the economy. It then moved over Greenland, causing a rate of melting not predicted for another half century.
The Napa Valley is concerned about the effect climate warming on their primary crop, Chardonnay grapes. In the last few decades the valley has moved to the high end of the range of optimum growing temperatures, and extensive planting is being done to explore which grapes can handle the heat. Northern California wine counties might have to replant completely or begin marketing varietal raisins.
People are also affected by heat. Humans are exothermic, giving off heat. Biochemical reactions in warm blooded organisms are most efficient, facilitating increased mobility and endurance. The human body core temperature is maintained in a range from 97°-99°F. When the core hits 99.5°-101°F, heat exhaustion sets in, which can disrupt the body's temperature regulation and lead to fatal consequences. At 104°F critical enzymes and biochemistry begin to fail. Cells start to die at 106°F and brain damage starts at 108°F.
To prevent these extremes, the body controls temperature by removing heat through radiation, exhalation, and surface cooling by evaporation of sweat. "Heat of vaporization" is the energy required to change water from liquid to vapor. The strong hydrogen bonds between water molecules give water a high heat of vaporization, 540 calories per gram. That is five times the energy required to change the temperature of the water from freezing to boiling. When sweat evaporates, it pulls energy from your skin and the air touching your body, giving a cooling effect. That is why it is important to keep your body hydrated, saturated with enough water that there is excess to sweat. Sweat contains dissolved salts to make it a better thermal conductor, which is why ingesting electrolytes while sweating is important.
Air at a given temperature can only hold a finite quantity of water vapor, and the humidity percentage defines how much of that total capacity is filled. Air with lower humidity can absorb more water vapor. Another measure is "wet bulb temperature", which indicates the lowest possible evaporative cooling temperature, based on the existing humidity and temperature.
When air is warm enough and humid enough, the body can no longer cool itself, and the core temperature begins to rise. The body begins to struggle when wet bulb temperature hits 90°F, making it hard to work outside. To put that in terms we already experience, that equates to 100°F with 67% humidity, 110°F with 49% humidity, or 120°F with 29% humidity. When the wet bulb temperature reaches 95°F, death occurs within 6 hours.
These levels are still rare, but warmer air holds more moisture, and these events will become more frequent. In 1995, a heat wave in Chicago hit a wet bulb level of 86°F. Saudi Arabia experienced 95°F wet bulb in 2003. In 2015 India hit 86°F wet bulb, while Iraq and Iran suffered through 92°F wet bulb. Within 50 years this will affect over 4% of the global population, including the American southwest.
Heat related wildlife and domestic animal deaths have increased in the last few years. This summer the US military has experienced heat related deaths during training, and the triple digit heat a few weeks ago affected construction and agricultural workers. In developed countries, increased heat means increased air conditioning usage, which adds to the grid load, usually increasing production of greenhouse gases, which accelerates temperature rise.
Gradual increase in heat is not the only concern. Within the last two decades, flash droughts have been identified. These are periods of extreme heat and low humidity that develop in a matter of weeks and can last for months, devastating agricultural production. As the planet heats, and climate becomes more turbulent, these events will happen more often.
The climate we grew up with has become unstable, and civilization as we know it is at risk. It will be expensive to respond, but lethal to ignore.
