Jacob, USA asked:
I've read that painting rooftops white can help to cool cities. So does ploughing away the snow warm the earth up and add to global warming?
We put this question to John King from the British Antarctic Survey in Cambridge:
John - Well, the thing about snow is that it’s quite reflective compared to bare ground. A good thick snow cover will reflect back up to 80 percent or even more of the sunlight that’s falling on it. Whereas bare ground or grasslands might only reflect 10 or 20 percent of the sunlight falling on it and so, the sunlight warms it up considerably. So, if you replace that bare ground by snow cover, then a lot of the sunlight that would’ve heated the ground just gets reflected back into space. So, if you remove a snow cover by ploughing it up or sweeping it away or whatever, revealing the bare ground underneath, then the ground is going to absorb a lot more sunlight, and will warm up a lot more quickly than if the snow were there. We are having an effect on the reflectivity, the albedo of the planet by changing land use for instance; cutting down forests and replacing them with grasslands. But that generally has the opposite effect, forests absorb quite a lot of sunlight, grassland is less reflective. People have suggested that we could partially offset global warming by painting the roofs of all of our buildings white. I think some calculations have been done that have showed that this will be a good thing, but it wouldn’t have a very large effect because you're only talking about a rather small area of the planet that you'll be changing the reflectivity of.
Yes, the impact of ice and snow reflections have been appreciated for a long while. This is why an ice-age is a positive feedback loop: more snow and ice means more energy reflected back into space, which means a cooler planet, which means more snow and ice and so on. What arrests - and reverses - these processes though, I'm not sure.
The way I understand it is, snow reflects sunlight off the Earth's surface, which by itself would help cool the Earth by preventing some of the sun's energy from being absorbed into the Earth's surface; however, an increasing layer of carbon dioxide traps the reflected enegy, heating the earth up more, melting the polar icecaps, killing us all. BechtelEngineer, Mon, 5th May 2014
Suntan lotion is a good idea for spring skiing as one gets a "double dose" of sunlight when out on the slopes.
I don't know how good the scientific evidence for snowball Earth actually is, but it's often claimed that the whole world once froze over and would have remained locked into that state ever since if it wasn't for the mechanism of CO2 from volcanoes building up to the point where the whole lot rapidly melted from equator to poles. David Cooper, Wed, 7th May 2014
Hi, my name is Thomas Ackerman, I would like to add some information to this page on common logic and viewed experience. I like in Saskatchewan, Canada and from my experiences with many many winters is that when the sun is shining the lack of cloud coverage allows all the warmth from the snow to escape. Let me explain.... The ice the snow consists of can only reach 0 degrees celcius at which point it freezes and expands and becomes locked. Meaning it will get no colder than that. The snow actually staying at 0 keeps the air above and the earth below to be regulated. Cloud cover holds the warmth in so to speak. ANYBODY living in this climate sees this clear as day. As for the snow reflecting radiation, thus, heat back out into space I must conclude from my observations of winter climate over 35 years that on years where there is less snowfall and ground coverage the average temperature outside is actually lower and I hypothesize that this is the reason. Energy reflected by snow and ice is immiscule to the actual amount of heat energy that becomes licked in the ice and insulated from the elements which on a sunny day can reach -70 degrees. But on cloudy days the snow warms the environment and stabalizes ground freeze. As many scientist have suggested snow and ice in larger than usual accumulations do result from previous overheating but a worst case senario that covered the whole planet and left us without any warm zone would not last very long because it naintains that 0 degrees which is not that bad and anything actually exposed to open air and the sun becomes way colder than 0 degrees celcius. If anything snow and ice coverage during the winter contributes to global warming by way of insulating the surface. KeizerPaPa, Sun, 20th Jul 2014
You would think that it actually warms it because sense the light is being reflected that the UV rays are going to go somewhere in the air.. I heard that you can get sun burned from the snow.. if you expose yourself to it Oceanbliss, Tue, 16th Dec 2014
Snow being subject to its own limitations only reaches 0 degrees Celcius.
It's important not to confuse several mechanisms at work here.