All energy on Earth ultimately comes from the sun. It is the sun's radiation that warms our planet- a characteristic that helps Earth sustain life. The radiation from the sun reflects off of the surface of the Earth and is emitted back into the atmosphere. Then, the atmosphere bounces the radiation back downward and some is lost to space as heat. This is called the greenhouse effect.
The gases emitted from the burning of natural resources cause the radiation that is reflected back upwards to not only reflect back towards Earth, but to be scattered throughout the atmosphere horizontally. Thus, the heat is trapped. This causes the temperatures on Earth to increase over time and is known as global warming. Global warming is what is responsible for the scenarios mentioned withing your question: rising temperatures, desertification, and rising sea levels (the warmer temperatures cause the ice near the poles to melt).
All these related to each other and are the effects of global warming, which is nothing but enhanced green house effect. A number of gases in our atmosphere, including carbon dioxide, absorb the infra red emissions from the earth's surface and help keep the earth warm. However, human activities are continually increasing the concentration of these gases in the atmosphere, which is causing a rise in our global temperature. This temperature increase will cause glaciers to melt, which will increase our sea levels. Rising temperatures will also cause more evaporation of surface water. This, combined with regional changes in climate, will cause changes in our biosphere. Incidents of desertification and droughts are also a possibility due to global warming. Realizing these dangers, many nations are working towards reducing their emissions of green house gases.
Hope this helps.