It's been more than half a decade since Al Gore's An Inconvenient Truth got us thinking and talking about climate change. And while the scientific consensus continued to solidify and our atmosphere continued to fill with more greenhouse gasses (we're now only a couple of years from crossing the psychologically painful threshold of 400 ppm), we actually changed very little in terms of our lifestyles and our national policies.

Some blame our collective inertia on bigger and more urgent concerns, like public finances and health care -- but that thinking would be based on an assumption that there's really nothing big or urgent about climate change. Could that be true? Or could it be that, while we understand all the theory about a changing climate, we may not actually know how it really affects our lives today and tomorrow?

Think about it: Al Gore's movie talked about melting glaciers and (slowly) rising sea levels; scientists have been talking about a few degrees of global warming and about a very changed world by the end of this century (how many of us plan to be around for the year 2100?); politicians are setting emission reduction targets for the year 2050. It's all too abstract and distant -- and none of it could possibly feel like a big deal, the way a mortgage default or a national bankruptcy would hurt today. And yet, if you break down this big fuzzy issue and you start to look at how it's affecting our economy already, how it will mess up our lives in the not too distant future and what will happen to the moral legacy of our generation, it suddenly starts to feel like a really big and scary deal. Consider this:

Short-term economic impact. The innovators, the visionaries and the nimble ones are already responding to the carbon crunch, even though it's still barely noticeable to the naked eye. China is already becoming the world's leading builder of smart grids, fast trains, solar arrays and everything else that a post-carbon world will need. Australia just became the first country to impose a nationwide carbon tax, forcing a great new dose of energy-related innovation into its economy. Some American states are seriously considering banning the sale of high-carbon oil from the Canadian oil sands. So you and I are already being impacted by climate change -- because we're either going to have to join this economic revolution (which might be a bit of an uncomfortable adjustment) or we can choose to resist it at our economic peril. This is not future-talk; it's happening all around us, right now. Elections are being lost and won on this issue; investment fund flows are changing; and tomorrow's leaders are launching their careers with entirely new perspectives and passions. Climate change has already changed the way our world works.

Long-term lifestyle impact. This is the scarier stuff, but most of us have been tuning it out because it's almost unbelievable -- and because it's always easier to focus on more immediate plans. Two or three degrees of warming may not sound like much, especially when it happens over decades, but it's the kind of shock the planet hasn't experienced since the extinction of the dinosaurs. It takes an incredible amount of order and balance to keep seven billion of us living on this small planet in relative peace. None of us can imagine what will happen if that balance is suddenly thrown off; if tens or hundreds of millions of hungry and thirsty people need to find a new homeland; if regional wars break out over access to water; if a resource-rich nation suddenly goes bankrupt. The domino economic effects and the security threats will touch every one of us, no matter where we live and no matter how safe and wealthy we may feel today.

The legacy of our generation. We didn't create this mess -- we simply continued contributing to it. Climate change is the product of lifestyles from the past nearly ten generations (ever since the start of the industrial revolution) -- but nobody before us knew as much as we do about these consequences, so that makes us truly the first and only generation that is knowingly wrecking this world for our kids. If we don't at least try to change our ways, then those who follow us will naturally point the finger only at us. We will be known as the most selfish generation; the ones that knew what needed to be done but were too self-absorbed, too greedy or too lazy to do anything about it. Legacy is a big deal -- particularly when we get old and start packing our bags for the final exit -- so let's not underestimate how we, the first climate-change-aware generation, will be feeling near the end.

Climate change is the biggest, most complex, multi-faceted and perhaps incomprehensible challenge humanity has ever faced. If we choose to stick our heads in the sand, we might be able to convince ourselves for a little while longer that the party will last forever and the world doesn't need to change. But the world around us is already changing. If we want to protect our prosperous lifestyles, raise our kids in a safe and stable society and be remembered fondly by our grandkids, then our only option is to become the generation of innovators for humankind.