> The rate at which an object can reflect solar radiation is called its albedo [source: Budikova]. The bigger the albedo something has, the better it reflects radiation. Traditional asphalt has a low albedo, which means it reflects radiation poorly and instead absorbs it.
Asphalt has an albedo of ~0.05 - which means it absorbs ~95% of solar radiation. Tarmac is ~0.1 - which means ~90%.
> Asphalt is a mixture of aggregates and bitumen that needs up to two days before it completely cures. Whereas, Tarmac is a combination of crushed stone and tar that cures quickly.
https://tarmacdriveways.ie/key-differences-tarmac-vs-asphalt...
rainfall (you could probably spray the runway and it will cool down and be dry quickly…)
Length of day (we’re about 1 month past the summer solstice in the N. Hemisphere, and days are long in the northern latitudes)
Shade (unlikely on runways, they’re in the sun all day)
Wind (probably best anywhere on a runway unless it’s in a valley)
Cloud cover during the night: can’t radiate to the universe where it’s about -273C if clouds are in the way.
On my first time in the Nevada desert I was astonished to find that I needed a jacket at dawn to stay warm, after all kinds of daytime heat. Looking at Elko NV's weather this week, it's got highs of 99F/37C and overnight lows of 61F/16C
The sky around where clouds are might be around -20C, while outer space is at -273C or so, so you get much more radiative heat loss in the latter state (clear sky).
(This is also why you’ll see gardeners try to cover their plants when there’s a “frost warning” even though the temperatures won’t be going below freezing).
And from the opposite perspective, the sun is really far away but incredibly hot, so it transfers heat to us, and more as you get closer (and less as you get further away).
Which happens to be close to the color of adobe. I'm yet again starting to think that native peoples were onto something.
This is one of the main reasons people are so worried about it being "too late" to fix climate change. There are positive feedback loops like this where a little increased heat causes even more rise in temperature.
It takes a lot of high albedo area to effect the overall climate. For example, melting ice caps do decrease the albedo of parts of the Earth, accelerating climate change. Large scale increases to Earth's albedo in the form of space mirrors were seriously considered as options for global warming mitigation as late as the Obama administration. However, the risks of unintended modifications to the environment (e.g. crop failures, unpredictable weather) are generally considered too great. At present, space mirrors, with an estimated lifetime cost of $5 trillion for 50 years of cooling, could be a decent "last resort" option compared to the possibility of spending hundreds of trillions upfront to permanently solve the problem with carbon capture (although cost estimates vary widely based on the amount of CO2 that needs to be captured).
Other options include stratospheric aerosol injection (https://en.wikipedia.org/wiki/Stratospheric_aerosol_injectio...) which could minimize the effects of climate change for as little as $55 billion/year, and marine cloud brightening (https://en.wikipedia.org/wiki/Marine_cloud_brightening), which could cost as little as $5 billion/year. Possible side effects might include ozone depletion and acid rain for aerosols. Marine cloud brightening could cause weather changes.
So yes, you could manipulate albedo but it will always come with side effects and costs.
Greenhouse gases absorb infrared radiation emitted by the Earth and heat the atmosphere as well as the surface. SRM geoengineering just changes how much energy the Earth absorbs from the sun (which has the strongest effect at the surface).
If GHGs increase, but you use SRM to keep the surface temperature fixed, you still end up heating the atmosphere. This means in a geoengineered world, you have less rain.
A reduction in rain might be more important to some countries than others - not everyone would want the same amount of geoengineering.
(Edit: I apologize for the uncalled for smugness. But "albedo" is not some special physical quantity, it's literally a measure of how light/dark colored a material is. "Alba" is Latin for "white". Although granted, albedo is usually measured across the whole spectrum, not only the visible part.)
I well remember working on my parents' car in Phoenix summers. The chromed wrenches on our driveway surface got to instant-blister temperatures. Tools with black surfaces were uncomfortable to pick up, but were usable.
The chromed tools had a lower absorption of sunlight than the black tools, but their IR radiation coefficient was even lower. So equilibrium temperature (at which radiated energy = incident energy) was much higher for the chromed tools.
(Used to live in Glendale.)
It's not as simple as color.
In particular, there are dark things that have an albedo higher than asphalt's 0.05...
What would the sky be obstructed by? Clouds? How could that affect how cool tarmac on the ground gets at night?
With a clear sky, you're radiating (based on your own temperature) out to the blackness of space, which is radiating back at 4 Kelvin. Which is to say, it's contributing basically nothing. You're just giving up heat to the cosmos.
With a cloudy sky, you're radiating (based on your own temperature) out to the bottoms of the clouds, which are reflecting your radiation back to someone else on the ground, and their own heat is reflecting back to you. And such. The cloud looks white in the daytime because it's very reflective, so it acts like a mylar blanket to hold the heat in.
> At night, when cloud coverage increases, downwelling infrared radiation also increases. So, clouds act like space heaters, emitting energy towards the ground. Blankets only limit the transfer of heat energy away from your skin(convection).
So they turn them on the blow the stagnant warmer ambient air around and mitigate that.
This is why heatsinks are often painted black.
It is also the reason for all the strange white/black colors on rockets.
Errata: “heats less quickly”.
And don't forget the 10,000 rule: https://xkcd.com/1053/
> Traditional asphalt has a low albedo, which means it reflects radiation poorly and instead absorbs it
Seems like a pretty good high level explanation of why that matters. Darker objects absorb energy instead of reflecting it. I'm sure there's more to it than that when you get into details.
Unlike car tires where people may switch them between climates/seasons, aircraft tires need to be fairly universal.
Ground temperatures are almost entirely responsible for the majority of the thermal energy/temperature put into the air, down at the surface.
> really getting quite tiresome and making it harder to respect the real problems
I agree that it trivializes and undermines the real problem of global warming. People have this false implicit assumption that if global warming is real it must be possible to immediately perceive it, and instead of challenging that, we keep trying to inject drama and danger into familiar experiences, and it just rings false. On a subconscious level, I suspect we all know it's silly. Also, what happens if it's not this hot next year? After spending 2022 essentially telling people that they can directly perceive global climate trends by walking outside, what will they think if the summer of 2023 is relatively cool?
I'm probably wrong, I'm not an expert in public opinion, it just feels false.
The hottest temperature ever recorded here isn't some niche thing like most rainy April for 5 years. Also maybe the fact that there's constantly new unusual weather should tell us something.
Latitude of London, UK: 51.5° N
To be clear they are talking about the air temperature rather than runway temperature and I've added the latitude so you can understand why it's a big deal that London has hit 40 degrees.
That’s weird, some cursory searches show a definite upward trend for quite some time, i do find these weird sites where they consistently pick outliers in a dishonest manner. It really wouldn’t be worth engaging with them though
Yuma's 4 runways total 543,000 sqm. At midday those runways are absorbing 543MW of energy from the Sun. So that might require 100-200KW of electricity to run the heat pumps. And then you still need somewhere to dump the heat.
In short, I think the reason they don't cool runways is due to the cost.
Also I don't know of any skating rinks that operate outdoors in summer, or to use a more favourable example, something like lowering a surface temperature from 20C to -5C (an ice rink, indoors) vs lowering a surface temperature from 80C to 55C (an assumption for a runway, outdoors). Even Dubai, a major transport hub, much hotter than UK even this week, with cheapish energy costs, little public debate uses other mitigations such as runway materials and scheduling many takeoffs for 2-5AM (there are many costs due to high temperature besides runway degradation).
Airplanes are very heavy so this may not be physically possible, but if you could run coolant pipes under runways, couldn't that captured heat be used in energy production elsewhere?
0 - https://en.wikipedia.org/wiki/List_of_solar_thermal_power_st...
Yuma International/MCAS has roughly 540,000m^2 of runway (plus taxiways).
International hockey rinks are 30m by 60m. My local airport, which isn't that big as far as these things go, has two runways each of size 45m by 2200m. That's 55x larger per runway.