Hundreds of thousands of people participated in the People's Climate March in New York City today, in an attempt to get both the US and international governments to take climate change seriously. The UN summit on climate change is set to begin on Tuesday - it's a hopeful sign although, given the outcomes of other climate summits (Kyoto Protocol, I'm looking at you), it doesn't actually mean anything will come of it.

Despite government action or inaction, there are a number of scientists working on ways to slow or reverse the effects of climate change - big geo-engineering projects. Those may provide some of the best solutions, at least in the short-term, and at their core, they follow the same basic physics of climate change that were mentioned in my last post.

So you don't have to go to another post, here's a quick review of the physics.

Climate change is brought about by:

1) How much energy we get from the sun (i.e. sun cycles, our orbit around the sun)

2) How much of that energy is reflected back into space (by polar ice caps, glaciers, various aerosols)

3) The amount of greenhouse gases in earth's atmosphere (water vapor, carbon dioxide, etc.), which absorb the energy that is being reflected.

Those same bits of physics, says Jim White of INSTAAR, apply to potential solutions. Geo-engineering projects could deal with the problem of climate change by:

1) Blocking sunlight (i.e. putting a giant sunshade into space)

2) Reflecting sunlight back into space (i.e. mirrors, gigantic chunks of styrofoam in the ocean)

3) Removing greenhouse gases from the atmosphere (artificial trees are one idea that's on offer)

The best option, in White's opinion, is getting greenhouse gases out of the atmosphere. Here's why:

We've already got close to 400 parts per million of carbon dioxide (CO2) in the atmosphere. CO2 is one of those greenhouse gases that traps heat inside Earth's atmosphere and could, eventually, raise global temperatures by as much as 3° C.

Now that temperature increase hasn't happened yet - currently, temperatures on Earth still reflect an earlier time, when there were fewer CO2 particles. There's something of a time delay here, part of which is due to the fact that Earth is a water planet (think of all our oceans) and water takes a long time to heat up.

But, much like water set over a burner, eventually that water will get warmer and Earth's temperatures will go up. And that's even if we stopped emitting all greenhouse gases right this very minute (an unlikely and impractical scenario). CO2 remains in the atmosphere for hundreds of years. So even if we use our geo-engineering skills to block sunlight or reflect it back, that 400 parts per million stays at the same level - meaning will we still have the same amount of greenhouse gases in the atmosphere and we'll still get those warmer temperatures.

But our third option - removing greenhouse gases from the atmosphere - gets to the root of the problem. If we can vacuum up some of that CO2, we could potentially counteract some of the changes we've already seen and avoid a further increase in temperature.

It's obviously a lot more complicated than what I'm writing here - and there are plenty of financial and bureaucratic hurdles - but scientists do think its feasible and there are a number of projects in the works.

The thing to remember about all of this, though, is that we're talking a pretty long time table, like more than 100 years. It's going to require commitments that extend through several generations and reach across international borders.

People and nations will have to suspend their own immediate interests and play the long game. It can't be something that one nation does or that one generation begins - it's a serious, long-term investment and it's one that we, ourselves, won't see the outcome of. Today's marches - in New York and worldwide - and Tuesday's meetings seem to indicate that we might be able to move in that direction.