  We investigate dynamics of accretion discs of young stars with fossil
large-scale magnetic field. Our magneto-gas-dynamic (MHD) model of the
accretion discs includes equations of Shakura and Sunyaev, induction equation,
equations of thermal and collisional ionization. Induction equation takes into
account Ohmic and magnetic ambipolar diffusion, magnetic buoyancy. We also
consider the influence of Ohmic and ambipolar heating on thermal structure of
the accretion discs. We analyse the influence of considered dissipative MHD
effects on the temperature of the accretion discs around classical T Tauri
star. The simulations show that Ohmic and ambipolar heating operate near the
borders of the region with low ionization fraction (`dead' zone). Temperature
grows by $\sim 1000$ K near the inner boundary of the `dead' zone, $r\approx
(0.5-1)$ au, and by $\sim 100$ K near its outer boundary, $r\approx (30-50)$
au.
