The Ross River Virus issue is a little different, because it's an Australian disease that may be increasing its range within that country. The likes of dengue and chikungunya are appearing in countries far from where they have traditionally been found. And a big part of the reason for that is that people have brought them there.
Greenland Mosquitoes on the Attack as Climate Warms
The extent to which humans are transporting themselves, and their belongings, across the globe, is continuing to expand, and invasive species are coming along for the ride. The Asian tiger mosquito, the vector for chikungunya, made its way to Europe and North America via eggs attached to used tires and lucky bamboo. This increased movement of people is likely for now the single greatest factor behind the spread of infectious diseases, including those transmitted by mosquitoes.
Of course, the mosquitoes would not be able to thrive in their new countries were conditions not suitable for them, and by and large, the picture is that, overall, a warmer, wetter environment can be expected to increase mosquitoes' range and the time available to them to complete their life cycles. The WHO has even concluded that a global temperature rise of 2-3 degrees C will increase the number of people worldwide at risk from malaria by 3-5 percent, which works out at several hundred million.