1 . The cooling effect of trees reduces the surface temperature of European cities in the summer by up to 12°C in some regions. In contrast, green spaces without trees have an insignificant effect, according to a study that strengthens the case for tree planting to help cities adapt to global warming.
Jonas Schwaab at ETH Zurich in Switzerland and his colleagues used land surface temperature data collected by satellites to compare the temperature differences between areas covered by trees, treeless urban green spaces, such as parks, and urban constructions such as roads and buildings. They analysed 293 cities from across Europe.
The land surface temperature measured by satellites isn't the same as the air temperature, which is more closely linked to what humans would feel, says Schwaab. "Usually, the air temperature difference between tree-covered areas and built-up areas would be much smaller than the land surface temperature differences," he says.
The team found that tree-covered areas in cities have a much lower land surface temperature compared with surrounding areas. The differences were between 80C and 12C in central Europe and between 0°C and 4°C in southern Europe.
The cooling effect of trees comes largely trom shading and transpiration（蒸腾）. This process takes heat energy from the surrounding environment for evaporation（蒸发）, lowering the surrounding temperature. In the warmer climate of southern Europe, the soil is typically drier, so the cooling effect of transpiration is lower than in regions further north, says Schwaab.
The team also found that the cooling provided by treeless green spaces is insignificant, and in some instances green areas without trees can even be warmer than the surrounding urban areas.
Extreme heat is a growing problem for cities in Europe and elsewhere as the planet gets hotter. The findings show that trees can have a big influence on cities across Europe, but since the size of their effects varies, heat reduction strategies should be tailored to suit each region, says Schwaab.
1. What's the purpose of the study?| A．To measure land and air temperatures. | B．To suggest planting more trees in cities. |
| C．To make people aware of global warming. | D．To stress the importance of green spaces. |
| A．The soil is drier | B．The climate is coluer. |
| C．There're more green spaces. | D．There're more roads and buildings. |
| A．Wet lands should be enlarged. | B．Dry soil should be reduced. |
| C．More roads should be built. | D．Solutions should be different. |
| A．Trees Cool the Land Surface Temperature of Cities. | B．Researchers Raise Solutions to Extreme Weather |
| C．High Tech Lowers Land Surface Temperature | D．Extreme Heat Does Harm to the Environment |
