A sharp fall in electricity demand in NSW and a continuing surge in hydropower means carbon emissions are now 10 million tonnes lower on an annualised basis since the introduction of the carbon tax, research shows.

The monthly carbon emission index produced by consultants Pitt & Sherry shows emissions from generators in the national electricity market serving eastern Australia in April were 6 per cent lower than last June.

Further electricity price shocks are on the way.

The share of output from coal-fired generators remains at its lowest since the market began in 1998 at 74.6 per cent while the proportion from hydro and wind farms has climbed to a record 12.8 per cent. Gas contributed 12.6 per cent.

Since June, output from Snowy Hydro is up 57 per cent while the Tasmanian hydro system is supplying 25 per cent more electricity.