These are very different type of marches but the search for truth is common to both. The election of Trump has given the country an alternative to the search for truth which is government propaganda. The country seems torn between this choice. The truth can be very unpleasant and can challenge one's fundamental beliefs so government propaganda can be very appealing to some people. On the other hand, propaganda can be very dangerous and when it comes to climate change can lead to the collapse of civilization so the rational choice in the long run is the search for truth.
Be aware that the nuclear lobby is trying to hijack the March For Science. Nuclear proponents, especially those for "New Nuclear" e.g Small Modular Nuclear Reactors, And Thorium Nuclear Reactors, have set up a new campaign - called "Generation Atomic". This campaign especially targets young people.
Their sophisticated campaign argues that nuclear power is necessary to combat climate change. they pretend to support renewable energy, but subtly downgrade it.
They argue that ionising radiation is not so bad, perhaps even beneficial.
They depict anti nuclear people as a"anti science". Nuclear advocates often claim that anti nuclear people are "anti everything" - anti medicine, anti vaccination etc.