Carry trades seek to make money from the fact that the interest rates set by central banks around the world vary considerably. In Japan, for example, the lending rate has been close to zero for some time and is still only 0.5% today – the lowest for any major currency – whereas in Australia it is 6.5% and in New Zealand 8%.
Investors seeking to exploit these differences typically borrow cheaply in Japan to fund investment in assets, such as bonds in the higher yielding currencies hoping to benefit from the large difference in interest rates. This works provided the yen doesn’t suddenly strengthen against the other major currencies. The effect would be to create large capital losses especially for investors who borrowed heavily to fund carry trading.