All the Way

Fossil Fuels need to be removed entirely from the energy system in order to save the climate, that is clear. Renewable energy (solar, wind, tidal, etc) will need to replace this as source. To make this work well, we need to change how we use our energy. Without fossil fuels, the mantra is: Use electricity where possible, use alternatives (such as hydrogen, methanol, ammonia, ...) where electrification is not possible.

... of TRANSPORT wherever possible: this uses half the energy of Hydrogen.

We need to get rid of fossil fuels. An often mentioned alternative is be Hydrogen, but Hydrogen is wasteful: changing over to hydrogen would massively increase global energy use.
For trains: electric overhead lines waste less than 5% of total energy, batteries waste less than 5% of total energy each cycle, but batteries need more energy to make.
The making and storing of green hydrogen loses 40% of energy: 5-10% when making it from electricity, and then each storage cycle loses up to 30%. Then converting hydrogen back to electricity to run the train or car loses another 50% of the energy.
Using fossil-fuel based hydrogen makes things far worse and unsustainable: "Blue hydrogen" is made from natural gas (and doesn't exist at any scale), loses 20% energy to make, another 25% to “store” the CO2 (if we can), another 30% to store the hydrogen, and then STILL emits all the upstream methane and CO2 from gas exploration and production, and emits another 10% of total CO2 during the process. So using "Blue hydrogen" wastes energy, and produces similar greenhouse gas emissions to burning natural gas .