WASHINGTON - President Obama signed an executive order Thursday dictating the federal government will cut its greenhouse-gas emissions 40 percent over the next decade from 2008 levels and increase the share of renewable energy in the federal government's electricity supply to 30 percent during that same period.

Simultaneously, federal suppliers including Honeywell, IBM, General Electric, and other major U.S. firms are pledging to reduce their own carbon footprint by 5 million metric tons over the next 10 years compared with 2008 levels. Taken together with the new executive order this would cut overall U.S. emissions by 26 million tons by 2025, the equivalent of taking nearly 5.5 million cars off the roads for a year.

"America once again is going to be leading by example," Obama said at the Energy Department.

"We're proving that it is possible to grow our economy robustly while at the same time doing the right thing for our environment and tackling climate change in a serious way," he said.

Although the government is the largest U.S. energy consumer, it is responsible for less than 1 percent of annual U.S. emissions - and a far smaller chunk of emissions worldwide.

White House senior adviser Brian Deese estimated the new measures would save $18 billion; the federal government has already cut its overall emissions 17 percent since Obama took office, saving $1.8 billion.

The executive order detailed how the government will meet the new target. This will include reducing energy use in federal buildings by 2.5 percent per year between 2015 and 2025, instructing agencies to obtain 25 percent of their energy from carbon-free sources by 2025; and increasing the carbon-per-mile efficiency of federal fleets 30 percent from 2014 levels over the next decade while increasing the percentage of zero emission and plug-in hybrid vehicles in federal fleets.