How can we lower Earth’s temperature? One way is called geo engineering which means modifying the climate in various ways such as using reflectors to reflect the heat of the sun back into outer space. A way to do this is by making more clouds to reflect the sunlight back into space before it heats up the surface. That was discussed recently in, How to fix the global warming problem for a while using kites and water pumps, where clouds were manufactured by pumping water up to heights and sprayed into the air. Mentioned in passing was the painting of portions of the Earth with a white paint such as titanium oxide. Aside from the expense, there is a difficulty with this method if it is applied where there is snow accumulation because soon the very highly reflective paint would be covered with lower reflectivity snow which would degrade the cooling effect.
A better way than direct application to the surface would be to have reflective shades over the surface of a high latitude lake at in Canada or Siberia. That would permit the heat of the sun to be reflected back into outer space so the water being shaded would remain cooler. Being cooler the lake would freeze sooner in the winter, stay frozen longer in the spring and as the lake melted in the summer would put cooled air back into the atmosphere. The lake being frozen over and covered with snow would reflect more light and help to get greater efficiency out of the system. At higher latitudes the roofs would be tilted away from the sun for greater reflective efficiency. They need not cover a whole lake but only enough to increase the rate of freezing and turning the lake snow-white sooner. Lakes appear black when viewed from above which means they are absorbing light and heat so freezing them earlier in the fall would mean they absorbed less total light during the year.
These light reflecting shades could be made in many ways. Some could be made into permanent structures which once built would give global cooling effects for many years. A quick alternative would be to lift sheets of reflective mylar on balloons over high latitude lakes where the sun is at a low angle so the shadow would cover a larger area. The shade could be tilted to an angle which would reflect the incident light up toward a cloudless sky. One advantage of the mylar reflective sheet system is that the mooring point could be moved to track the sun which would increase the shade-mirror’s efficiency. The shade could be hung on a pole or strung between existing trees.
Another use for these shades would be to shade those areas where there is warming muskegg releasing methane. By keeping the top layer of soil colder for longer there would be less release of this greenhouse gas.
It would probably take a shadow on a lake about 30×30 meters in an ideal location to equal one small cars heat output. But it the expense of building such a shadowed frozen spot could be built into the price of the car it represents there would be no additional global warming from that car.