Video report by ITV News Correspondent Ivor Bennett
Doctors are wearing white surgical masks to represent the number of people who die prematurely from air pollution per day on average.
They marched to Parliament Square to lay out 180 pairs of shoes to mark 180 weekly London deaths from pollution, according to Extinction Rebellion.
Several climate activists leading the crowd are wearing hospital breathing masks, and others are carrying Extinction Rebellion flags and signs reading: "Climate change is a health issue."
One protester said raising awareness about the effects of climate change on health is part of their "duty of care as healthcare professionals".
Alex Turner, 36, a paediatric and emergency doctor from Bristol who was wearing his blue scrubs and stethoscope, said: "We are meeting outside Shell because they are one of the biggest companies involved in the oil and energy industry, and they have real power to decarbonise that industry.
"We are protesting illegal levels of air pollution."
Julia Simons, 23, a final year medical student at Cambridge University, said: "Our Government has the responsibility to explain (climate science) to its citizens, to understand that if they don't act radically, that future which I've been studying for won't exist."