I’m in New Zealand. My good friend is in Melbourne.
In the part of New Zealand I’m in, we’ve had some really got days. Like, not coping, many cases of heat stroke etc.
Whereas, heat like that is more normal for him. Is there a reason that 25°c is hotter here in NZ than Australia?
In: 15
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Probably humidity. Humidity makes the intensity of the heat worse in 2 ways.
First, it’s because it makes our body‘s cooling mechanism less effective. Our body cools itself by sweating and as that sweat evaporates, it cools the surface of our skin. High humidity means there’s more moisture in the air around us. For our sweat to evaporate, there needs to be a differential between the level of moisture in the air and the level of moisture that we’re sweating out. The more moisture in the air, the lower that differential, the less our sweats evaporates.
Second, is because the specific heat capacity of water. The specific heat capacity describes how much energy it takes to warm (or cool) a substance. Since there’s more water suspended in the air when there’s higher humidity, if temperature of the day is hot and that moist air is heated up, then it takes longer for the air to cool. So it will retain more heat for longer and will feel hotter than a place that is the same temperature but not as humid.
More UV radiation is getting through, due to a thinner ozone layer and clean air.
The Ministry of the Environment have a good explainer:
*The thickness of the ozone layer in the atmosphere varies seasonally. At mid-latitudes, such as New Zealand, it is thickest during spring and thinnest during autumn. This means the ozone layer over New Zealand thins during summer, providing less protection from UV sunlight when we are closest to the sun and the sun is highest in the sky. Moreover, our summertime ozone layer is thinner than the summertime ozone layer experienced at corresponding Northern Hemisphere latitudes.*
*The air in New Zealand tends to be clearer than that in many other locations. UV sunlight travelling through the atmosphere to Earth’s surface is scattered or absorbed by clouds and aerosols (air pollution).*
As a result of this, in summer, daytime levels of UV are often extreme on UV indexes. So you can have a lower temperature than Oz, but a higher UV level. Hence it feels hotter.
Source: [https://environment.govt.nz/publications/our-atmosphere-and-climate-2017/exposure-to-ultraviolet-sunlight/new-zealands-uv-levels/#:~:text=At%20mid%2Dlatitudes%2C%20such%20as,is%20highest%20in%20the%20sky](https://environment.govt.nz/publications/our-atmosphere-and-climate-2017/exposure-to-ultraviolet-sunlight/new-zealands-uv-levels/#:~:text=At%20mid%2Dlatitudes%2C%20such%20as,is%20highest%20in%20the%20sky).
Humidity and average temperatures play a role.
If you’re used to very hot summers on average, an extra hot day won’t feel so bad. used to more mild temps and a heat wave will overwhelm people whose bodies are not acclimated.
As for humidity, the main way humans cool off is by sweating. sweating relies on evaporation. High humidity interferes with evaporation.
Common American joke about places like Arizona, Nevada… “But it’s a dry heat!”
So is a pizza oven.
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