On a macro and micro scale, greenroofs reduce "greenhouse gas emissions", have an impact on humidity, air quality and reflect heat from rooftops keeping interiors cooler and reducing A.C. energy and expense. In conjunction with other green installations, greenroofs can play a role in altering the climate and even the weather of a city as a whole. Greenroofs also remove heavy metal particulate materials from rainwater and dramatically reduce runoff and decrease the need to expand related wastewater infrastructure. Greenroofs reduce exterior noise pollution, often by 40 to 50 decibels. Tax credits for greenroofs are available in many urban jurisdictions including New York, Chicago, Washington D.C., Minneapolis, Portland, Maryland, Seattle and others.