Turton s 20150708_1500_upmc_jussieu_-_amphi_herpin

Steve Turton

College of Marine & Environmental Sciences

Expansion of the tropics: evidence and implications

The Tropics are expanding…

Estimates from more than 30 peer-reviewed studies puts the rate of pole-ward expansion of the tropics since 1979, somewhere between 1.3–2.5 deg. latitude or 140–280 km, per 25 years. (Isaac & Turton, Essay 5, State of the Tropics Report, 2014).

What is driving this expansion?

Research has identified that the primary drivers are likely to be greenhouse gases, black carbon, aerosols and other man-made pollutants, though this is expected to be an area of research that sees further developments in the near future. (see review by Isaac & Turton, 2014)

(Source: IPCC AR5 2013)

2025 2090

8.5

2.5

Future climates

(Source: IPCC AR5 2013)

Future climates

Global implications

Drought, drying and shifts in climatic zones

Shifts in tropical cyclone tracks and activity

Impacts on biodiversity & ecosystem services

Potential expansion of pests and disease (see review by Isaac & Turton, 2014)

Global implications

Subtropical, more arid conditions, may be seen in regions at higher latitudes which have historically enjoyed a more temperate climate, with implications for management of water resources, agricultural systems and biosecurity risk (esp. Mediterranean systems).

However, some regions which currently border the equatorial zone may experience an increase in extreme rainfall, which could result in flooding, the displacement of communities and increased incidence of disease.

No analogues for thermal regimes for the deep tropics (thermal equator).

Increased rainfall in higher latitudes.

Mediterranean climates

Source: gimcw.org

No analogues for the thermal equator

The mean annual position of the thermal equator is near 10° N latitude.

Regions of current and future mega-cities (<10 million)

Global implications

The pole-ward expansion of the Tropics appears to be linked to a simultaneous expansion in the tracks of tropical cyclones, potentially bringing cyclonic activity to regions which have previously not experienced such weather events and this will impact on human health, biodiversity and the economy.

The burden of vector-borne diseases on health and the economy of the Tropics may also increase as more regions become climatically suitable for insect vectors.

Global implications

The Tropics are the most biodiverse region on earth, with more endemic species and more biodiversity ‘hotspots’ than anywhere else.

However research suggests that although many species are tracking climate changes, species in the Tropics may be lagging behind the rate of tropical expansion – meaning some species may not be able to sufficiently track their preferred environment and climate and may potentially risk extinction.

Species restricted to ‘sky islands’ in particular.

Species that occupy narrow thermal regimes, e.g. coral reefs

Conclusions

The Tropics are expanding pole-wards at a significant rate (could be 850 km expansion by 2100).

Expansion will exacerbate drought and drying in warm temperate regions as the dry sub-tropical zone shifts pole-ward with likely increases in rainfall in higher latitudes and the deep tropics.

Shifts in tropical cyclone tracks and activity is likely.

Impacts on biodiversity & ecosystem services is certain.

Potential expansion of pests and disease will follow the shifts in climate zones.