Boston-area hospitals cut their energy greenhouse gas emissions by 29 percent between 2011 and 2015, and are on track to reduce 33 percent by 2020, according to a new report released by Health Care Without Harm. The report includes data from hospitals serving on the Boston Green Ribbon Commission’s Health Care Working Group. Their trajectory delivers a 47 percent reduction in greenhouse gases compared to “business as usual” by 2020.

With these reductions, Boston healthcare facilities are exceeding mandated greenhouse gas reduction goals set by the City and Massachusetts, which aim for 25 percent by 2020, working towards 100 percent by 2050. The 47 percent reduction is equivalent to eliminating the annual greenhouse gas emissions of 42,220 passenger vehicles.

Twenty percent of the hospital sector greenhouse gas emission reductions come from significant investments in renewable energy. Partners HealthCare is purchasing low-impact hydropower, and will buy most of its electricity from a new wind turbine farm in New Hampshire, as it works to make its huge health care system net carbon positive for all energy by 2025. Boston Medical Center is slashing energy use and neutralizing its electricity emissions through a North Carolina solar energy farm, and expects all its energy to be climate neutral by 2018.

The greenhouse gas reductions come while the hospitals are providing more patient care, doing more energy-intensive medical research, expanding facilities, and coping with hotter summers, all of which should have pushed energy use and emissions upward, according to Health Care Without Harm’s report, which analyzed more than 24,000 records covering 22 million square feet of hospitals.

The report identifies areas where Boston hospitals made notable progress between 2011-2015 compared to business as usual in energy efficiency, conservation and greenhouse gas reductions, including a reduction in total energy use of 9.4 percent; a reduction in electricity use of  13.1 percent; and a reduction in natural gas of 26.1 percent. This generated enough cost savings to cover health care for 1,357 Massachusetts Medicare enrollees. And according to the U.S. Environmental Protection Agency, a $15 million cost savings is the equivalent of the hospitals finding $300 million in new revenue every year.