Heat is energy and when you add energy to any system changes occur.
Because all systems in the global climate system are connected, adding heat energy causes the global climate as a whole to change.
Much of the world is covered with ocean which heats up. When the ocean heats up, more water evaporates into clouds.
Where storms like hurricanes and typhoons are forming, the result is more energy-intensive storms. A warmer atmosphere makes glaciers and mountain snow packs, the Polar ice cap, and the great ice shield jutting off of Antarctica melt raising sea levels.
Changes in temperature change the great patterns of wind that bring the monsoons in Asia and rain and snow around the world, making drought and unpredictable weather more common.
This is why scientists have stopped focusing just on global warming and now focus on the larger topic of climate change.