Businesses and city administrations are becoming "increasingly significant" actors in the fight against climate change and are set to contribute national-scale emissions cuts, new United Nations research has revealed.

Programs brought in by such non-state actors, a label that includes regional and sector-wide climate change initiatives, could avoid close to 1.8 gigatons of carbon dioxide equivalent (GtCO2e) in 2020, according to a new study by the United Nations Environment Program (UNEP).

Such savings could prove decisive if the world is to meet emission reduction targets likely to be agreed at the Paris climate conference in December.

"Government pledges are currently expected to deliver an impact of between five and seven GtCO2e by 2020, highlighting the significance of the estimated emissions reductions from non-state actors," said Achim Steiner, U.N. Under-Secretary-General and UNEP Executive Director.

The emission reduction impact of corporations alone is likely to reach 0.63 GtCO2e, but with the top 1,000 largest GHG-emitting companies responsible for annual emissions of 10 GtCO2e, or around 20 percent of the global total, UNEP says there is the potential for far greater savings in the future.

Meanwhile, the report argues that action by the world's cities, which produce almost half of all greenhouse gas emissions, are central to tackling climate change.

Three city initiatives analyzed by UNEP demonstrate how urban centers could cut emissions by 1.08 GtCO2e in 2020, while the Climate Group's States and Regions Alliance could bring 0.76 GtCO2e of additional emissions reductions in the same year.

"UNEP research shows that we need to move towards carbon neutrality by mid-to-late century to head to keep global temperature rise to below 2 degrees C," Steiner added. "Meeting this target cannot be reached through government action alone. Initiatives by cities, businesses and industrial sectors to cut emissions can contribute and support national emission commitments, bringing significant savings of CO2 equivalent."

One such corporate initiative is the Climate Group's RE100 campaign, which aims to persuade the world's most influential companies to commit to using 100 percent renewable power within a specified timeline.

Having already attracted the likes of BT, IKEA, Marks & Spencer, H&M, Nestlé, SAP and Unilever, RE100 on Monday signed up U.S. software giant Autodesk as its 20th company.

Autodesk already uses renewables to meet 40 percent of its global electricity consumption, up from 33 percent last year, and has now set a target to source 100 percent of its power from renewable sources by 2020 or sooner.

"With the cost of renewable energy falling, U.S. companies are increasingly opting for clean, local energy supplied at competitive prices," said Amy Davidsen, executive director of the U.S. office of the Climate Group. "The business case is clear — and 100 percent renewable power is within reach."