Final answer:
The expected effects of projected 21st-century climate change on malaria include increased transmission in higher altitudes and an expansion of malaria-prone areas, while changes in mosquito populations may vary with specific conditions.
Step-by-step explanation:
The expected effects of projected 21st-century climate change on malaria include a variety of impacts on the transmission and spread of the disease. Increased transmission in higher altitudes is expected due to rising temperatures making these areas more conducive to mosquito habitats. Additionally, there could be an expansion of malaria-prone areas as warming allows mosquitoes that carry malaria to survive and breed in regions that were previously too cold for them. In contrast, mosquito populations may decrease at very high temperatures above 30°C, which is the upper limit for parous females, potentially reducing offspring production. However, this is offset by increases in the range and lifecycle acceleration of mosquitoes due to generally warmer temperatures. It's important to note that while higher temperatures can limit reproductive capabilities, drier conditions are also significant; below 60% humidity there might not be much change in the population of mosquitoes. In summary, it's a complex interplay of factors, with both increases and decreases in transmission dependent on specific regional climatic changes.