Ocean currents are constantly moving streams of water that circulate around the globe in patterns similar to winds. Warm currents flow along the equator and towards the poles, while cold currents carry polar waters to the equator. Local wind patterns are influenced by nearby landforms, and mountains can create rain shadows on their leeward sides with dry conditions. Human activity also affects the climate through burning fossil fuels in cities and industries, which contributes to the greenhouse effect and global warming. Deforestation of rainforests releases harmful gases and reduces rainfall levels by decreasing transpiration from fewer trees.