Greenhouse gas emissions during this year's dry autumn rose 25% compared with the previous autumn as the country resorted to fossil fuels to avert a possible electricity shortage.
A big drop in hydro generation because of low lake levels corresponded with a leap in the amount of electricity generation from fossil fuels.
Electricity output from coal and gas-fired power stations rose 15% compared with a year earlier.
There was also lower output from wind farms because of a large number of still days.
The figures, from the Ministry of Economic Development, cover the June quarter.