Whatever you believe about the existing reserves and undiscovered sources of fossil fuels and other combustible or radioactive minerals, they will eventually be exhausted or too expensive to extract.
Energy policymakers and planners act as if we had that kind of time. Unfortunately, we don't.
As the science clearly shows, CO2 and other greenhouse gas emissions must peak and begin to decline in less than a decade if we are to meet the target of staying below 2 degrees Celsius of global mean temperature rise - the target to which the 192 member governments of the United Nations Framework Convention on Climate Change are committed.
As the new Intergovernmental Panel on Climate Change (IPCC) report on climate impacts, released in March, clearly shows, anything more than 2 degrees Celsius, and human civilization as we know it (not to mention the rest of the biosphere) is in serious jeopardy.
So, the question about a 100% renewable-energy future becomes not if but how and, most importantly, how quickly can we do it, and how much will it cost?
"It doesn't cost the world to save the planet", said IPCC working group III co-chair Ottmar Edenhofer when unveiling the "mitigation" portion of the IPCC report in Berlin in April. Meeting climate targets on the basis of what we know now will cost somewhere in the vicinity of 0.06% of annual GDP growth for the rest of the century — and that is not counting the lives that will be saved or much of the climate damage avoided.
But, surely renewables can't do it on their own? Today, no. Tomorrow, why not?
While you will find no shortage of experts who will say that renewables cannot fully power our energy system, you see precious little analysis to back up these statements. One generally hears something like: "What do you do when the sun doesn't shine or the wind doesn't blow?", and then they go on to tout their favourite technology, whether it be nuclear, "clean coal", carbon capture and storage or some other variation on the energy system that got us into this mess in the first place.
They conveniently forget that while wind and solar PV are variable renewables, hydro, biomass, solar-thermal and geothermal are not. They forget that Brazil, Norway and New Zealand are nearly at a 100% renewable electricity supply, and that Denmark, Sweden and others are already moving in that direction.
They forget that with broader grid coverage areas and strong interconnections, power can be moved about quite efficiently, and they forget the growing movement of homeowners and businesses shifting increasingly towards self-sufficiency, primarily through the use of solar PV and other small-scale technologies whose costs have come down drastically in recent years.
With sufficient storage (pumped, compressed air, batteries, fuel cells), sufficient dispatchable renewables, and energy efficiency, energy conservation, smart grids and demand-management systems, it is certainly technically feasible to power our economy completely on renewable energy, as various simulations in different parts of the world have shown.
Further, in the places with large renewable-energy penetration such as Denmark, you see a much greater role for electricity in the overall energy system, not only for transport but for heating as well.
The fact is, a 100% renewable-energy future is technically feasible, and at low or no cost to GDP, especially when you consider the fuel savings involved for most economies and, not to forget, the necessary removal of the $650 billion a year or so in subsidies to fossil-fuel production and consumption. The question is whether it is politically feasible.
It may sound like a typical disaster movie, but we really do only have a limited time to act before climate impacts could move from bad to catastrophic, taking decisions out of the hands of democratically elected governments and put first in the hands of the emergency services, and ultimately, the military.
Let's not mess around the fringes of when the higher capital costs of investing in a renewable future will be repaid. It will be paid back by fuel savings, and reduced spending on the disaster-movie elements such as refugee camps and fire-fighting.
The real question is not whether or not we can afford it. We very clearly can't afford not to.
Steve Sawyer is CEO of the Global Wind Energy Council