Essay 5 Expansion of the tropics - evidence and implications

[Extract] There is accumulating evidence that the tropical zone is expanding poleward in both hemispheres, and that the subtropics are also expanding into regions which have previously enjoyed a more Mediterranean climate. This essay is a follow-up to an initial report by the same authors conducted in 2009; there has been considerable further work in this field since 2009 and so we include up-to-date research, investigate how thinking has changed, or not, and whether predictions from five years ago still hold true. A poleward expansion of the tropical and subtropical zones is likely have significant consequences for a number of the issues raised in the State of the Tropics Report (2014), including the peoples of the Tropics, and for ecosystems and biodiversity. For example, The State of the Tropics report highlights that the resources required to sustain larger populations and economic growth are putting significant pressures on the natural environment in tropical regions. An expansion of tropical regions will only increase these demands further, and may also cause a shift in ecosystems as some regions will become drier, and others may see more frequent heavy rain events. The Report also highlights the fact that almost half the human population of the Tropics is vulnerable to water stress – a shift in climatic zones, and potentially drying in regions currently neighbouring the subtropics could increase the number of people who are at risk. Furthermore, the State of the Tropics report finds that despite improvements in health and nutrition over the past 50 years, the Tropics still bears a 'disproportionate share of the global burden of many communicable and preventable diseases.' An expansion of the tropical zone could increase the prevalence of many diseases, particularly vector-borne diseases, as more areas become climatically suitable for insect vectors