By Roland Buerk
BBC News, Tokyo
Mr Hatoyama has pledged to change the way Japan is run
Even before he has been confirmed as prime minister, Yukio Hatoyama has made a big announcement.
Mr Hatoyama told the Asahi World Environment Forum in Tokyo that Japan would aim to cut emissions of greenhouse gases by 25% from 1990 levels by 2020.
It is a clear break with the past.
Only back in June outgoing Prime Minister Taro Aso of the business-friendly Liberal Democratic Party (LDP) committed the world's second-biggest economy to a cut of just 8% over the same period.
Mr Hatoyama led his Democratic Party of Japan (DPJ) to a landslide election victory over Mr Aso's LDP at the end of August and is expected to be formally named prime minister when parliament meets on 16 September.
The DPJ's manifesto laid out how it intended to achieve the reductions.
There are plans to cap emissions and set up a domestic trading market.
There are pledges to prioritise the renovation of existing housing, as well as to subsidise solar panels, "green" vehicles and energy saving appliances.
The move has certainly pleased environmental campaigners, who had condemned the earlier pledge as inadequate.
"Japan used to be the country driven by industry groups, but now we see a new prime minister with true leadership," said Takamasa Higuchi of WWF Japan.
"We welcome the courage of Yukio Hatoyama and believe he has the strength to set Japan on track for a low carbon future which will benefit people and nature, both in Japan and worldwide."
The business lobby is likely to be concerned about the feasibility of the target, though, and campaign against it.
"Industry is already at the edge of what they think can be done," said Martin Schulz of the Fujitsu Research Institute in Tokyo.
"They are already the most CO2 efficient around and cutting further is very expensive."
Mr Schulz said the 25% target was not "outrageously high", only just beyond what the European Union is pledging.
The announcement on climate change is just the start of the changes the DPJ and Yukio Hatoyama want to make.
Business fears it is already at the edge of what can be achieved
During the election campaign they put forward a vision of a Japan that many people cling to but fear they are losing, a largely equal society where salary men have a job for life.
The feeling was those certainties had been swept away by the reforms of former Prime Minister Junichiro Koizumi that allowed companies in more sectors of the economy to take on temporary workers.
Where the LDP put the interests of corporations first, the DPJ wants to focus on consumers, such as by giving generous child allowances to families.
More than that, the DPJ vowed to change the way Japan is run, moving away from the iron triangle of the LDP, the bureaucracy and business.
For decades it produced breakneck growth, but in recent years had stultified.
"The first priority was the economy after World War II," said Hideki Wakabayashi, a former DPJ member of the House of Councillors, now visiting fellow at the Centre for Strategic and International Studies.
"That's where the LDP has put the emphasis. There was no strong opposition party to put emphasis on the consumer side, on the people side.
"The economy is very important still, but I think not from the supply side. [It's now more about] the people side, increasing domestic consumption to boost domestic demand."
But even as they went to the polls, many voters were concerned whether the DPJ would be up to the job.
It has never held power before, a large proportion of its members of parliament are wet-behind-the-ears newcomers.
And the new government wants to bring in change while at the same time reforming the very instrument through which it wields its power - the bureaucracy.
"The result in terms of actual policies will be that the DPJ cannot do much without the bureaucracy," Martin Schulz says.
"Many laws and regulations for the next year are already drafted. Wherever they want to change much they will run into consistent resistance from the bureaucracy which they will not be able to overcome. And it will be very messy and time consuming."
Japan's election marked the end of a system that had endured since the end of World War II.
The challenge Yukio Hatoyama faces is to build a new model to take its place.