Homo sapiens use about 18 terawatt hours of energy each year, enough to keep 18 billion phones charged all year (if that helps). On average, we waste more than half of that. Leaky houses, inefficient transport, wasteful industry – the world is essentially keeping the radiator on next to an open window.

But this is not such a depressing picture as may first appear, as improving these leaks in our energy system are among the cheapest and easiest ways to take action on climate. We may be able to power most of our future power growth with efficiency savings, and that’s a big deal.

There are plenty of ways to begin – take homes, for example. Money spent on things like insulation and double-glazing generally pays for itself within a few years, and is a fine way for governments to provide stable jobs while doing good for the world. Smart meters are already making homes more efficient by deciding the optimum time to use energy-hungry appliances, and much more.

Then there’s food, which we seem to enjoy ploughing great amounts of time and energy into growing, before throwing a large portion of it in the bin. We should probably change this. We’ll also talk about how the choices we make while choosing from shelves or menus have a huge effect on the world around us, and how we can transform our food system into a more streamlined beast with less wastage at every step.

There are surprisingly large gains to be had from small changes: one airline estimates they’ll save 326 000 gallons of jet fuel a year by switching from paper manuals to digital tablets in the cockpit. On the ground, fuel economy in cars could save 5 million barrels of oil each day in the US alone, and that’s worth fighting for.

There’s also the issue of our crumbling electricity grids – which will have to be replaced at some point anyway – and what we replace them with. Instead of spending billions to simply replace what we have, we could construct a smart grid that has the flexibility to adapt to renewable power sources, a grid that uses high-voltage DC cables to efficiently transfer power where it’s needed (with massive energy savings in the process). Constructing this grid will create jobs – lots of jobs – and very likely work out cheaper than business as usual.

It’s worth noting that the technology to do all this is already with us – we’re not waiting for a tech billionaire to step up, nor for a wonder fuel to be developed, we just need governments to step up and make them a priority. It’s low-hanging fruit, waiting to be plucked.