The reasons for the phenomenon shown in the cartoon (Figure 5) are (a) global warming, (b) population increase, (c) desertification and (d) wetland destruction.

This topic discusses the effects of global warming. The impact of global warming: leading to the adjustment of the ecosystem; Lead to sea level rise; It may lead to an increase in disasters such as droughts, floods and rainstorms; The threat to human health will increase. The reason for the phenomenon shown in the picture is the melting of polar glaciers caused by global warming. So choose option a in this question.