The finalised ''Clean Power Plan'', by Mr Obama and the US Environmental Protection Agency, will require power plant owners in each state to cut carbon dioxide emissions by 32% from 2005 levels by 2030 and put the focus on renewable energy sources.
Announcing the measures at the White House, Mr Obama said drastic action was required or it might not be possible to reverse the effects of global warming - or adapt to it.
Climate change posed the greatest danger to this and future generations he warned, saying: ''There is such a thing as being too late.''
Mr Obama has clearly heeded the increasingly urgent warnings made by the Intergovernmental Panel on Climate Change. The panel was established in 1988 under the auspices of the United Nations and has 195 member countries.
Its work means there has slowly been more consensus between scientists and governments about the human cause, speed and severity of change, and action and responsibility for tackling the issue.
The panel's latest reports leave little room for manoeuvring on the subject. They show total carbon dioxide emissions from fossil fuel combustion and industrial processes have continued to rapidly increase.
The reports warn that, without reductions, there will be significant global temperature increases, which scientists fear will lead to rapid sea-level rises, mass extinctions of plant and animal species, and food shortages.
The 2014 reports give a 15-year timeframe for urgent action to reduce greenhouse gas emissions to limit the global temperature increase to 2degC above pre-industrial levels.
This year's United Nations conference on climate change (in November and December) seeks to achieve that goal by creating a universal and binding climate agreement between all countries.
Mr Obama's plan is the most significant step taken so far to tackle the issue. Coming only months ahead of the UN meeting, it sends a message to the world and shows sorely needed leadership. But so it should.
The United States and China are the biggest emitters of greenhouse gases. Without action from them, there is little impetus for smaller emitters to follow suit.
It won't be easy to make the changes. The solutions are complex and the action costly. Big business interests in the US energy sector have already vowed to fight Mr Obama's plan.
Given the policy is one he can pass without Congress obstruction, there is likely to be some cynicism about the fact he did not implement the unpopular changes earlier in his first or second terms, when he could have had a chance to see them through.
After all, if the Democratic Party loses next year's presidential election, the plan is likely to be shelved.
But someone must make the first move and, with the Paris talks looming, the onus is on all nations to make the necessary commitments.
That includes New Zealand. There is understandable concern over the impact on our dairy industry - our biggest emitter. But climate change will impact on other vital sectors and export earners if we do not reduce our carbon footprint.
Increased government investment in research and development is necessary to enable scientists to explore the alternatives and provide support for emitters to make the changes.
Where there is a political will, there is surely a way. Most fundamentally, that needs to start with changes in attitudes. Division is not going to get the world where it needs to be in the timeframe given.
Rather than reactionary statements like a ''war on coal'' for example, businesses and governments need to be proactive, realise they are on the ''same side'' and join forces to fight what is looming as our biggest common enemy.