With political efforts to slow global warming moving at a tortuous pace, some of the world’s largest companies are stepping into the void, pledging more support for renewable energy, greener supply chains and fresh efforts to stop the destruction of the world’s tropical forests.

Forty companies, among them Kellogg, L’Oréal and Nestlé, signed a declaration on Tuesday pledging to help cut tropical deforestation in half by 2020 and stop it entirely by 2030. They included several of the largest companies handling palm oil, the production of which has resulted in rampant destruction of old-growth forests, especially in Indonesia.

At a United Nations climate summit in New York this week, companies are playing a larger role than at any such gathering in the past — and issuing a blizzard of promises. Several environmental groups said they were optimistic that at least some of these would be kept, but they warned that corporate action was not enough, and that climate change could not be solved without stronger steps by governments.

The corporate promises are the culmination of a trend that has been building for years, with virtually every major company now feeling obliged to make commitments about environmental sustainability, and to report regularly on progress. The companies have found that pursuing such goals can often help them cut costs, particularly for energy.