(Michael Williamson/The Washington Post)

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.

Speaking to reporters Thursday at the Energy Department, Obama said that “America once again is going to be leading by example.”

“So 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.

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

The move comes on the day the president is meeting with Britain’s Prince Charles — a prominent environmentalist and climate change advocate — and his wife, the Duchess of Cornwall, in the Oval Office. Obama and Charles are slated to discuss the two nations’ efforts to address global warming, as well as encouraging corporate social responsibility, creating opportunities for young people and preserving historical and cultural ties between Britain and the United States.

The executive order details how the government will meet the new climate 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.

After signing the executive order at the White House, Obama toured the Energy Department’s rooftop solar panels and attended a roundtable there where some of the federal suppliers discussed their new climate commitments.The companies will publicly disclose how closely they are meeting these greenhouse gas reduction pledges over time.

The federal government is the largest energy consumer in the United States — with the military accounting for roughly half of its total energy use — though its greenhouse gas emissions constituted only 0.6 percent of the nation’s total output in 2013, according to federal data. Still, Christy Goldfuss, acting director of the White House Council on Environmental Quality, said federal actions can have a huge impact given its reach and the scope of its supply chain.

“President Obama has made it clear that climate change is an all-hands-on-deck challenge,” Goldfuss said, noting the federal portfolio boasts 360,000 buildings, 650,000 fleet vehicles, and $445 billion in spending on goods and services.

While the federal government met the climate target Obama set out in his first term relatively easily, it  has faced some challenges in reducing greenhouse gas emissions in some areas. The 2007 Energy Independence and Security Act dictated all new federal buildings and those undergoing major renovations had to use fossil-fuel free energy by 2030. The Energy Department has been slow to implement the rule, and a bipartisan coalition in the Senate is seeking to roll back the measure.

In October DOE put out guidance that keeps the target in place but allows for some exceptions, including an exemption if an agency determines that it is not technically practical to meet it.

Dave McCurdy, president and CEO of the American Gas Association, said in a statement that while his group supports federal efforts to address climate change the government shouldn’t make it harder for Americans to use natural gas.

“We have repeatedly reminded this administration about the benefits of direct use of clean natural gas in homes and businesses,” McCurdy said, ” Natural gas used directly for heating, water heating, cooking and clothes drying is the most efficient, affordable and environmentally friendly way to use this abundant, domestic resource.”

At the same time, the liberal think tank Center for American Progress issued a report Thursday finding that greenhouse gas emissions generated by gas, oil, and coal extracted from federal lands and waters accounts for one-fifth of the nation’s total carbon output.

The group–which is usually supportive of the administration, and employed both Deese and Goldfuss before they joined the White House–called the emissions “a blind spot in U.S. efforts to address climate change.”