1. Energy is the biggest single issue facing us as a species.
Global warming—by far the worst environmental challenge humans have ever confronted—results from our current fossil-fuel energy regime, and averting catastrophic climate change will require us to end our reliance on coal, oil, and natural gas. Ocean acidification is also a consequence of burning fossil fuels, and most other environmental crises (like nitrogen runoff pollution and most air pollution) can be traced to the same source.
Therefore ending our addiction to fossil fuels is essential if we want future generations of humans (and countless other species) to inherit a habitable a planet. But these energy sources are “unsustainable” also in a more basic, economic sense of the term: oil, gas, and coal are depleting, non-renewable resources. Already, depletion of the easy-and-cheap sources of petroleum that drove economic growth in the 20th century has led to persistently high oil prices, which are a drag on the economy. We have picked the low-hanging fruit of the world’s petroleum resources, and as time goes on all sources of fossil energy will become more financially costly and environmentally risky to extract. This is a big problem because the economy is 100 percent dependent on energy. With lots of cheap energy, problems of all kinds are easy to solve (running out of fresh water? Just build a desalination plant!); when energy becomes expensive and hard to get, problems multiply and converge.
One way or another, whether our concern is the environment or economic growth, it’s mostly about energy.
2. We are headed toward a (nearly) all-renewable-energy economy one way or the other, and planning is essential if we want to get there in one piece.
If society is to avoid civilization-threatening levels of climate change, the use of fossil fuels will have to be reduced proactively by 80-90 percent by 2050.
At the same time, despite the claims of abundance of unconventional fuels (shale gas, tight oil, tar sands) by the fossil fuel industry, evidence overwhelmingly shows that drillers are investing increasing effort to achieve diminishing returns. Either way, fossil fuels are on their way out.
Most nations have concluded that nuclear is too costly and risky, and supplies of uranium are limited.
That leaves renewable energy sources—solar, wind, hydro, geothermal, tidal, and wave power—to power the economy of the future.
3. In the process of transition, the ways that society uses energy must change at least as much as the ways society produces energy.
Every energy source possesses a unique set of characteristics: some sources are more portable than others, or more concentrated, intermittent, scalable, diffuse, renewable, environmentally risky, or financially costly. We have built our current economy to take advantage of the special properties of fossil fuels. The renewable energy sources that are available to replace oil, gas, and coal have very different characteristics and will therefore tend to support a different kind of economy—one that is less mobile, more rooted in place; less globalized, more localized; less when-we-want-it, more when-it’s-available; less engineered, more organic.
At the same time, the sheer quantity of energy that will be available during the transition from fossil to renewable sources is in doubt. While ever-more-rapid rates of extraction of fossil fuels powered a growing economy during the 20th century, society will struggle to maintain current levels of total energy production in the 21st, let alone grow it to meet projected demand. Indeed, there are credible scenarios in which available energy could decline significantly. And we will have to invest a lot of the fossil energy we do have in building post-fossil energy infrastructure. Energy efficiency can help along the way, but only marginally.
source Richard Heinberg museletter 258