I had the occasion to stumble upon two uniquely imagined facets of the same future over the past week. The first: The World Without Us, an eerily quiet scenario in which humans disappear from the Earth and nature slowly and persistently takes over. The second: Children of Men, a visually stunning dystopia in the form of a sterile and slowly vanishing human race.

Alan Weisman’s The World Without Us uses a rational, scientific approach to describe post-human Earth. Surprisingly, the book reads like a summer page-turner…that really makes you think. The story meanders from the planet’s wildest places - a primeval forest in Belarus and Poland - to areas where human conflict has driven human abandonment and nature has found peace - in Cyprus and Korea.

Weisman’s artistic description of what falls apart, what lasts, and what happens when we’re gone is like candy for the imagination. "In a dream, you walk outside to find your familiar landscape swarming with fantastic beings. Furry rhinoceroses, big hairy elephants, and even bigger sloths-sloths??" He continues, "a dream, or a congenital memory? This was precisely the world that Homo sapiens stepped into as we spread beyond Africa, all the way to America. Had we never appeared, would those now-missing mammals still be here? If we go, will they be back?"

He also describes how man-made structures would fare the conquest of nature. For example, even on a sunny day, the people who keep New York City’s subway system working have to pump 13 million gallons of water away. Without us, Manhattan would soon turn into a system of streams and rivers. Weisman paints a vaguely haunting picture of the future, but at the same time, it’s powerfully peaceful.

Children of Men explores a slightly different future. Faced with mass infertility, our flimsy facade of civilization quickly degenerates into widespread warfare and depravity. We continue to destroy not only our own creations, but also our planet. The cause of human sterility is never explained in the movie, but one cannot help but connect the dots to the many chemicals and plastics that infiltrate our air and water today.

Weisman also explores infertility in The World Without Us - through the eyes of the founder of the Voluntary Human Extinction Movement, Les Knight. His image of a sterile population is much more peaceful: "Like retired business executives who suddenly find serenity by tending a garden, Knight envisions us spending our remaining time helping rid an increasingly natural world of unsightly and now useless clutter, in pursuit of which we’d once swapped something alive and lovely. ‘The last humans could enjoy their final sunsets peacefully, knowing they have returned the planet as close as possible to the Garden of Eden."

How/if we ever go, it will remain true that human action has fundamentally altered the Earth’s climate. The effects will persist for centuries, whether we’re here to feel them or not - but it’s certainly fascinating to imagine the world in a state that we, by definition, could never see: without us.

Your House Without You

Clint Wilder has taken up residence at the crux of the cleantech movement. Whether he’s hailing the mainstreaming of cleantech on Clean Edge’s website or touring the countrywith his new book, The Cleantech Revolution, (co-authored by Ron Pernick), he’s ready and willing to give you the skinny on just about any cleantech-related topic.

At heart of it, Clint and Ron’s new book is about the immense financial opportunity that lies in "any product, service, or process that delivers value using limited or zero nonrenewable resources and/or creates significantly less waste than conventional offerings." Following on the computer, Internet, and biotech revolutions, cleantech holds the promise to be the next turbocharged engine for economic growth both here in the US and abroad.

Among the usual suspects (solar, wind, biofuels/biomaterials, smart grid: "making improvements to the stupid grid"), the book includes a chapter that highlights how cities can get involved in the cleantech movement, entitled "create your own Silicon Valley." Each chapter of the book closes with ten important emerging players in the space. In true world-is-flat form, the authors noted emerging cleantech hubs in such diverse areas as Hyderabad, India; Austin, Texas; Shanghai, China; and Copenhagen, Denmark.

A related chapter, which actually didn’t make the final cut for inclusion in the book, was called "leapfrog nations." Herein, the authors describe how huge areas of India, for example, are off-grid - so individual communities and families often generate power onsite using solar, small wind, or biogas. The trend of note is this: rather than traditional grant-enabled work by the World Bank, more and more for-profit companies are now getting into these markets because they make financial sense for the first time.

I recently attended a reading of the book at Stacey’s here in San Francisco. When clean coal and nuclear came up at the end of the talk, Clint was asked to define the blurry line between technologies that can be considered cleantech and those that cannot. His response? "If they called it cleaner coal, I’d be more comfortable with that, but bottom line: they are not clean." He conceded that the efforts are good, but they just can’t be lumped under the same umbrella as solar and wind. Ain’t that the truth.

San Jose Mayor Chuck Reed, Councilmember Sam Liccardo, FST CTO Chris BeekhuisEditor's note: Sonia Aggarwal lives in San Francisco, and channels her passion for breakthrough renewable energy technologies into the Bay Area's lively world of cleanteach PR.

This Fourth of July, Fat Spaniel Technologies and the mayor of San Jose celebrate green as the new red, white and blue. On Monday, I headed south for a good old block party with a seriously high-tech twist.

Fat Spaniel founder and CTO, Chris Beekhuis, invited people to his house to charge up everything from electric vehicles to laptops using the excess power created by his solar energy system. Right now, if you use less electricity than your solar panels produce, you're exporting extra energy to the grid. However, you can't get a check from the utility company – you can only get a credit. This Energy Independence Day, Chris decided to share his sizeable solar credit with his neighbors and friends. He hasn't paid an energy bill in years because he got in on solar's ground floor.

He says, "In 1998, we installed a solar electric system on the side of our house. It was the second house in San Jose to do so. At that time, the utility did not have any standard testing procedures and we were expecting a return of something along the lines of 37.5 years. It was an act of passion, what I call Cleantech 1.0. Today things have really changed – our payback time has significantly improved."

Fat Spaniel Technologies was born and raised in Silicon Valley. Chris, a dataphile at heart, decided he wanted to measure exactly how much solar electricity his system was producing. So, he invented a software system that would make the revenue-grade information visible and accessible in real-time from any web-enabled device. Soon, the Fat Spaniel offering evolved into a highly visual dashboard displaying critical energy production information as well as fun tidbits like greenhouse gases avoided.

On this particular Monday afternoon in San Jose, it was so sunny that Chris couldn't give away enough energy to import anything from the grid…even though (true to Silicon Valley form) there were Blackberries, Trios, and electric vehicles galore sucking solar juice from the system. In a gratuitous effort to use up the three excess megawatt-hours of power, people brought vacuum cleaners to clean up the driveway, hair dryers (just in case the eighty degree weather wasn't enough) and an electric guitar for a solar-powered concert.

Mayor Chuck Reed touted solar's current reality and future potential:

We want to demonstrate the technology that's now available in Silicon Valley, where we are going to be the solar technology capital of the world. 95% of San Jose is already built. So that retrofit market is really important to achieve our overall goals of energy independence and getting as much energy as possible distributed in a way that it doesn't matter if the grid goes down, we're not out of business.

Try as we might, we only got to see 5% of Chris' extra clean power count down, but I would still say the event was a great success.