Expansion of the tropics: revisiting frontiers of geographical knowledge

The tropics are expanding poleward at an alarming rate—with massive implications for societies, economies, and natural environments. This expansion appears to be determined largely by anthropogenic drivers—notably rises in greenhouse gases. Of greatest concern is the poleward shift of the dry sub-tropical zone into highly populated regions that have generally enjoyed a more temperate climate.While the effects of latitudinal shifts of climate zones will be most severe in temperate regions outside the tropics, there will also be significant changes in climate within the tropics—notably unprecedented thermal conditions for hundreds of millions of people, along with projections for more extreme weather events. Australia’s geographical location makes it particularly vulnerable to an expanding tropics. As the tropics expand poleward, more of southern Australia will be influenced by the dry sub-tropical zone and associated reductions in winter rainfall. These drying trends are projected to continue over most southern parts of Australia this century, accompanied by rising temperatures and more hot days. Future rainfall trends for northern Australia remain uncertain, but there is an expected significant increase in the number of hot days, together with more extreme weather events. Future climate change in northern Australia has been ignored by the White Paper for the Development of Northern Australia (2015), bringing into serious question the feasibility and affordability of many of the development policies, plans, and projects promulgated in the White Paper. Even without climate change, the north faces many significant environmental and economic challenges for its future development.