There are so many elements to consider when discussing climate in Australia, the El Nino Southern Oscillation, East Coast Lows, Indian Ocean Dipole, Southern Annular Mode and the Indonesian Throughflow to name just a few. However, there is one system that does not get so much attention due to its relative lack of appeal – the Tropical Rain Belt. This is because all it is known for in Australia is that it brings the monsoon rains to Northern Australia every summer. However, recent research published suggests that the TRB’s impact is worthy of greater consideration in its impact on global climate.
By examining isotopes of oxygen in stalagmites in southern China and northern Australia over a 3,000 year period, researchers from Cornell College found that the rainwater ratios in between the two areas matched very closely. This meant sometimes there was a higher ratio in both, sometimes lower, having the result that the TRB would expand and contract in times scales of decades and centuries in addition to seasonal movement up and down the hemispheres. The conclusion that the TRB has expanded and contracted over 3,000 years would have had an impact on climate that has previously not been considered.
The importance of this research is that it affects the understanding of past drivers of climate change variability and the relationship between different systems. As an example, research has been conducted into the ability of tropical wetlands within the TRB to sequester far more carbon than temperate wetlands (although in the Southern Hemisphere they also emit more methane). If the TRB was to move into a contraction period, the carbon stored in these areas would be far more prone to being released as the area dries out and risk of fire grows, methane emissions would also likely increase.
The 3,000 year study period is valuable as recent research has variously suggested that the tropical rain belt is shifting into more northern latitudes as a result of rising carbon dioxide levels and temperature levels, depriving areas of Australia of monsoon rains or that the TRB is expanding generally. Going forward, the challenge for scientists is to work out how the modern levels of greenhouse gases will impact the contraction and expansion of the TRB, this will have flow on effects to biodiversity, development of industries and agricultural production.
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