Forest fire reduces the northern hemisphere temperature

For years, climate experts say forest fires will make the greenhouse effect worse, because they increase carbon dioxide in the atmosphere. But a recent study proved the opposite.

Hundreds of large forest fires have appeared in Canada, Russia, Norway, Sweden, Alaska state of the United States and many countries located in the North Pole during the past 10 years. Scientists have warned that global warming, longer summers and dryness of the atmosphere will make fires more frequent.

Snow covered the ground in the forest at Donnelly Flats, Alaska, after the 1999 fire. (Photo: Newscientist)

When the flames burn trees in the forest, an amount of carbon dioxide is released into the atmosphere. Therefore, scientists once thought that forest fires could be one of the factors that make climate warming faster.

However, a group of 17 experts at the University of California and the University of Florida (USA) confirmed that this argument is not true, at least for countries located in the northern hemisphere.

A research team at the University of California (USA) investigated the impact of a fire that burned 6.7 hectares of forest in Alaska's Donnelly Flats, in June 1999. They measured the parameters as a quantity Sun radiation, emissions and density of trees in fire places and surrounding areas.

All data is put into computers to form a model that reflects the climate trend over the past 80 years. The model allows scientists to consider how a fire affects the climate in the short and medium term.

The team found that the temperature in the place was burnt and the surrounding areas increased in about a year since the fire broke out. However, in the next 10-15 years, the temperature drops. In fact, during the 80-year period since the occurrence of the fire, the climate temperature has decreased markedly.

Snow is an important factor

Explaining this phenomenon, scientists think that after the fire is burned by fire, there is only snow left in the area. While the trees can absorb radiation from the sun, the snow reflects light back into the atmosphere. That's why when trees disappear, radiation from the sun is taken out into space.

Because the snow is covered with ash, during the time the radiation head from the sun is partially absorbed by the ash. That's why the temperature rises in a year later. When spring comes, snow melts and the ash disappears. By spring of the same year, only snow covered the burnt area and the temperature reduction process began.

" The process of temperature reduction compensates for the effects of greenhouse gases so it can be said that the impact of climate fires is close to zero if measured globally ," said James Randerson, of the University. California and the team leader, said.

Finally, the grass, shrubs and big trees also grow back in the burnt area. But experts at the University of Florida (USA) found, growing in place of coniferous trees are aspen leaves, bolts and deciduous trees.

Due to the large light green leaves, these trees reflect more solar radiation than conifers, so the process of temperature reduction continues. Different from coniferous trees - which never shed their leaves - newly deciduous trees in the winter, reveal the snow below. Therefore, in the winter, the sun is reflected back into the atmosphere throughout the year.

Researchers believe that the thickest leaf layer of the forest can only fully recover after decades. In the northernmost countries, every 80 to 150 years, forest fires often recur in the same place.

Climate experts predict that this time period will be shortened as global temperatures rise due to the greenhouse effect. This means that the coniferous trees will be burned again, causing the temperature in the northern hemisphere to continue to decline.

However, the study does not indicate that tree felling is a good solution in dealing with warming in the northern hemisphere.

Viet Linh