Many scientists believe that global climate change has already affected organisms on Earth—and will continue to do so in the near and far future. For example, a warmer world would cause the expansion of certain groups that spread in warmer climates, such as certain insects, algae, and nematodes; such changes could potentially change the landscape of infectious diseases. New species—from either mutations or those that thrive best in a warmer climate—could essentially introduce, or even reintroduce, harmful parasites into the world—ones that could affect not only humans, but other organisms, such as the beneficial insects that pollinate plants. New diseases—either from other organisms or more resistant bacteria and viruses—could also wreck havoc on organisms worldwide.