Two groups of researchers are independently trying to thicken Arctic sea ice in winter so that it lasts longer in summer and reflects more solar energy to space. They drill a hole, set up a pump, and pump up sea water to flood the surface. This makes the ice thicker because the surface is much colder than the water below. One of the challenges is the cost of on-site labor and fuel. So far, this is looking promising - the amount of additional energy reflected to space justifies the cost. Another challenge transporting people to suitable sites in mid winter. Researchers are testing small autonomous submarines that drill up through the ice from below and then pump water.