Raising the temperature of a system makes diffusion:

1. Temperature is a measure of the average kinetic energy of the particles. 2. More kinetic energy means faster random motion. 3. Higher temperatures increase the energy and therefore the movement of the molecules, increasing the rate of diffusion. 4. Nothing about heating makes a substance move against its own gradient. _Source: OpenStax Biology for AP(R) Courses (CC BY 4.0), Ch 5 'Structure and Function of Plasma Membranes', sections 5.1-5.4_