As that heat rises, some of it is 【小题1】 by gases in the atmosphere and reflected back towards the planet’s 【小题2】. Like the glass in a greenhouse 【小题3】 holds heat inside the building, gases in the air hold in heat around Earth. Scientists call this global heat-trapping 【小题4】 the greenhouse effect. The greenhouse effect keeps the temperature of our planet’s surface comfortably warm.

Several gases in the atmosphere 【小题5】 to global warming. The one you’ve 【小题6】 heard the most about is carbon dioxide. Carbon dioxide is a good heat-trapping gas—a greenhouse gas, 【小题7】 scientists say. 【小题8】 certain amount of carbon dioxide in the atmosphere is 【小题9】. In fact, you add some 【小题10】 the air every time you breathe out.