I am always amazed when Willis posts a new and novel way to look at current energy use and what that means in the Energy balance of the climate warming. This would suggest that 50 U.S. state all-time record high temperatures would happen. And they are man made. But have nothing to with CO2.
The Megacities Are Cooking
Willis Eschenbach / January 16, 2020
Guest Post by Willis Eschenbach
[OK, had to start over, had bad numbers for the areas. Graphics have been replaced. I was using “core area” but I should have been using “greater metropolitan area. All conclusions are unchanged.]
I got to thinking about the phenomenon known as the “Urban Heat Island” effect, or UHI. Cities tend to trap heat due to the amount of black pavement and concrete sidewalks, the narrow canyons between buildings that slow down the wind, and the sides of the buildings reflecting sunlight downwards.
As a result, cities are often warmer than the surrounding countryside. In some cities, it’s hot enough that it affects the local weather. Here’s a simplified diagram:
 Figure 1. A simple sketch of typical increases in temperature due to the Urban Heat Island effect.
What I was curious about, however, was another kind of urban heat effect. This is the heat from all of the energy used within the city—electricity, fuel for transport, fuel for heating buildings, all of it. Eventually, almost all energy ends up as heat. So I went and got the energy usage for 27 huge “megacities”, along with the area of the city itself. I then combined the two to give me a measure of citywide energy usage in watts per square metre (W/m2). As a measure for comparison with Figure 2 below, a doubling of CO2 is said to increase the “forcing”, the total radiant energy impinging on the surface, by 3.7 W/m2.
 Figure 2. Additional forcing from direct energy use. The energy data is paywalled. The link is to SciHub’s copy of the paper. It may have a “CAPTCHA” that asks you in Russian to type in a word to prove you’re actually a humanoid. Just type it in, it’s not Putin in disguise. This was surprising to me. I hadn’t expected the effect to be so large.
Finally, I converted the forcing to an equivalent warming. The Intergovernmental Panel on Climate Change (IPCC) fifth assessment report, completed in 2014, gave a likely “Transient Climate Response” of about 1°C to 2.5°C for each additional 3.7 W/m2 of forcing. I’ve used 1.5°C because the heat generation persists over time. As a result, the cities have had time to equilibrate to the additional heating. Figure 3 shows that result. |
