Choose the option that correctly sequences the following sentences:

1. World temperatures already have increased this century by about 0.6 degrees Celsius and are projected to rise by between 1.6 degrees and 3.8 degrees by 2100.

2. Current projections are that sea levels worldwide will rise by 15 to 90 centimeters by 2100, depending on whether action is taken to reduce greenhouse gas emissions or not.

3. Global warming is caused by the burning of large amounts of fossil fuels, such as coal and oil, which release gases that trap heat in the atmosphere.

4. Sea levels could rise as glaciers melted and the higher temperatures expanded the size of the oceans, threatening much of land, which was originally reclaimed.