It's natural to think about what the world might be like decades from now: What inventions will have radically changed lives, much as personal computers and the Internet have impacted everyone today? What will cars (if we still have them) and houses look like? What sort of clothes and hairstyles will people be wearing? Will space travel finally be common? How will most of us make a living?

And on the environmental front: Will there have been big effects from climate change? (And, if so, will scientists have been able to do anything about them?)

As Dan Bloom, an environmental activist now living in Taiwan, was musing about some of those questions – especially the ones relating to the environment and global warming – he wanted to galvanize young people to do something to make a difference.

So he decided to produce a YouTube video addressed to the graduating class of 2099, a "wake-up call" as he puts it in an interview with the newspaper of his alma mater, Tufts University in Massachusetts.

Although Bloom calls himself an optimist, in the interview he sounds pretty pessimistic on global warming, but expresses hope that humankind can changes its ways:

I am deeply concerned that by the year 2500, there won’t be a human world anymore. Earth will survive, but humans will be history. ... We have about 100 years to change our ways. I think we can do it. But time is running out.

Thus the video, which seems squarely aimed at the Class of 2009. (Will we still be arguing over fossil fuels 90 years from now?)

What interests me about Bloom's efforts is not the specific proposals themselves, but this idea of looking into the future to try to see what it might hold for the next generations.

So here's your opportunity to do the same. (Cap and gown and YouTube not required.) In less than 200 words, tell us what you think Earth will be like in 2099 – and why.