Cool roofs achieve cooling energy savings in hot summers but can increase heating energy load during cold winters. Therefore, the net energy saving of cool roofs varies depending on climate. However, a 2010 energy efficiency study looking at this issue for air-conditioned commercial buildings across the United States found that the summer cooling savings typically outweigh the winter heating penalty even in cold climates near the Canada–US border giving savings in both electricity and emissions. Without a proper maintenance program to keep the material clean, the energy savings of cool roofs can diminish over time due to albedo degradation and soiling.