Builders turn Tokyo into a greenhouse

Instead, they claim massive city construction projects are responsible for playing havoc with local weather patterns, sending the thermometer to a record 42.7C last month.

They also believe they have the answer: "wind paths" through the crowded city which would allow cooler air to flow across the city from the coast.

"The situation in the metropolitan district is very serious this summer," said Koichiro Ishii, of the Tokyo metropolitan government’s Research Institute for Environmental Protection. "This is brought about by waste heat being released from vehicle exhausts and buildings’ air conditioning systems, along with a decrease in the amount of green space in the capital."

The effect is exacerbated by the fact that the wind has nowhere to go.

This year the effects have been dramatic. The previous record 37 days of continuous heat above 30C was broken earlier this month. And on 22 July, 48 people were admitted to hospital in Tokyo with heat stroke.

The new heat hazard has been thrown up in the shape of the redevelopment of the Shinagawa and Shiodome districts of the city, right alongside Tokyo Bay.

"This ‘wall’ has definitely influenced the amount of wind that comes off Tokyo Bay and into the city," Mr Ishii said. "We are very interested in the impact of the redevelopment areas but as they are new we do not have enough monitoring data to clearly explain their full effects."

Environmentalists are calling for boulevards leading from the bay to be widened when old buildings are knocked down - or at least protected in their present state. This would allow the coastal breeze to sweep through central districts.

Citing a new report by professor Toshio Ojima, of Tokyo’s Waseda University, an environment ministry official confirmed that recent construction work at Shiodome has "disturbed" cooling sea breezes and contributed to higher temperatures in the city.

"The area that has been redeveloped used to be railway yards until it was sold off ten years ago," said Akinori Ogawa, a spokesman for the ministry.

"What used to be a large open space is now skyscrapers. Along with the ministry of land, infrastructure and transport, we are very concerned about the heat island problem and we are doing what we can to reduce it."

Companies are encouraged - with tax breaks - to plant gardens on top of their buildings to reduce the amount of heat that would simply be bounced off a concrete roof, Mr Ogawa said.

The wind paths proposal has proved highly controversial - the metropolitan government merely says it is studying the situation at the Shiodome site, which covers 30 hectares to the south of the city and has 13 buildings above 300 feet high.

"We do not believe this will have an effect on future construction projects and the metropolitan government is not thinking about measures to limit redevelopment schemes," said Jun Ishikawa, a spokesman for the city.

Any lessons learned in Tokyo will be closely followed by other world cities whose microclimates are proving fertile areas of research but a growing concern for politicians.

In some of the biggest cities in the world, including Los Angeles, Mexico City, London, Dallas and Atlanta, major temperature differences have been found between the urban core and the urban periphery.

The construction of Canary Wharf in London’s docklands area has also caused a recordable rise in the ambient air temperature by fractions of a degree, showing that the effect can even occur on a smaller scale within the urban microclimate itself.

The heat does more than simply create discomfort for city dwellers, it also bakes nitrogen oxides and volatile organic compounds (VOCs), turning them into smog. In Los Angeles, for every degree the thermometer rises above 21C (70F), the city experiences an average of three per cent more smog. Hospital visits climb too because smog aggravates chronic heart and respiratory ailments.

But it is not clear how many cities might benefit from the "wind paths" being proposed.

And while some Japanese scientists warn that further construction alongside Tokyo Bay should be halted and regulations need to be imposed to create broader streets to act as wind paths, others say the studies that have just begun will show that the effects of large-scale projects are minimal.