Most of the world's energy today comes from fossil fuels.
To really phase out all fossil fuel energy, the following tech is needed:
Energy storage, especially...
Sodium-ion batteries
Reason: Because lithium-ion is too mineral-intensive to scale up.
To be used for mid-range electric vehicles and smoothing out the day-night cycle of solar panels.
They don't even have to be as energy dense as lithium-ion.
Energy sources - some combination of
Solar panels without scarce minerals
Reason: Most of today's solar panels on the market are too mineral-intensive to scale up.
To be installed on as many rooftops as possible.
This could provide enough "general-purpose" electricity for homes, buildings and EVs, but not enough for heating in cold parts of the world.
Wind turbines
Mostly for producing hydrogen gas
Can later be burned for heating buildings and in combustion vehicles
Fuel cell vehicles are too platinum/palladium-intensive to scale up, but hydrogen production is not.
During local windy seasons, can also be used for electricity directly.
Thorium power
Note that other forms of nuclear are not viable to scale up
Conventional nuclear power uses too much uranium-235 (too scarce)
Uranium-238 breeder reactors have too many weapons proliferation concerns
Nuclear fusion probably won't be viable soon enough, even though it'll ultimately be the best option in the distant future.
Until the above tech is ready, developed countries must reduce energy demand - most effectively by...
Driving less
Individual action: Walk, bike, or use public transit.
Collective action: Making neighborhoods more walkabile and improving public transit.
Buying less new "stuff"
Individual action: Frugalism
Collective action: Fight against planned obsolescence
Yes, these actions would have the most impact - see this pie chart :File:energy-demand-pie1.png.
Note that climate change isn't the ''only'' major environmental problem. There's also habitat loss. The most effective way to stop this is via food:
Reason: Because agriculture uses more land than any other human activity.
Stop food waste
(both personal ''and'' business food waste)
Make food more plant-based
(both personal choices ''and'' systemic changes make a difference here)
Yes, these actions make the biggest difference, both for the environment and for ending global hunger.