One of the (1) causes in global warming is carbon monoxide. The more carbon monoxide in the atmosphere, the (2) less the atmosphere is able to clean itself. The result is a warming of the atmosphere, the so-called global warming, and possibly ozone damage.

Earlier, it was found that carbon monoxide was concentrated in the Southern Hemisphere, and could (3) be attributed to deforestation. Huge areas of forest and grasslands in South America and Africa have been burned, putting carbon monoxide into the (4) air. Recently, (5) however, the Southern Hemisphere has been found to be clean, while the Northern Hemisphere is more polluted than expected.

The latest research was (6) conducted during the northern winter. The high levels in the Northern Hemisphere could be because of this. In winter carbon monoxide is destroyed more slowly. There are (7) about 100 more fires burned in winter, and possibly industrial processes work harder. It could also reflect the ever-increasing (8) number of roads. Optimists hope that the reason (9) for of cars on the North has overtaken the South as the major area of carbon monoxide is that at last the burning (10) of 20 has stopped, or at least reduced.