It's official: the Imperial Palace is cool. Its green, rolling acres in the middle of Tokyo are so cool that city planners are hoping to spread some of its refreshing air among sweltering subjects who live and work nearby. Last summer, scientists monitored temperature fluctuations at six spots within the palace grounds. They learned that, compared with the surrounding city, the oasis of green is an average of 2 degrees Celsius cooler, with the maximum difference an impressive 4.3 degrees. For years, urban planners have been looking for ways to keep the metropolis cooler in Tokyo's increasingly tropical summers. The emperor's garden may prove to be the answer. The Ministry of the Environment is still congratulating itself on the efficiency of this summer's official 'Cool Biz' campaign, which encouraged people to ditch their suits and ties, and turn down the air conditioning. This reduced carbon-dioxide emissions by around 460,000 tonnes, the ministry estimates. Power companies' sales fell by some 20.8 billion yen (HK$1.35 billion) - but even they are pleased, because they have strict emissions targets to meet. Now the ministry is focusing most of its efforts on a 'Warm Biz' campaign for the coming winter - encouraging salarymen to slip on a pair of long underwear for the office rather than turning the heating up. But it's also looking at how to improve on the summer's achievements. This is where the emperor comes in. With more and more concrete, glass and steel being used in the city's expansion, Tokyo's 'heat island' effect is getting worse. Daytime temperatures remain above 30 degrees for weeks on end, and the young and elderly are particularly susceptible to heat stroke - virtually unheard of a generation ago. Green spaces have shrunk, while new skyscrapers have been built along the shore of Tokyo Bay in recent years. These towers block the cool ocean breezes that used to funnel through the city in the evening. This leaves residents mopping their brows from the end of the rainy season, in late June, until autumn's blessed relief in late September. Now work is under way in the streets that lead away from the palace: more trees are being planted in long rows to create 'wind passages'. Their shade will cool the ground and they will channel cooler air from the palace into the surrounding business and residential districts. Efforts are also under way to cover the flat roofs of office blocks and government buildings with greenery to absorb the sun's heat. New pavement tiles, which stay cooler by retaining moisture, are being laid. As for the palace, will it heat up when the cool air wafts into the city? The answer is unclear, but if that happens, the emperor could be forgiven for getting a little hot under his imperial collar.