The Ice Age can be explained by some well-placed specks of iron. Adding dust to the waters around Antarctica can supercharge plankton growth, causing global temperature drops. To stop climate change, we need a whole lot of iron filings.
Here's how the process works. Most of the time, the Southern Ocean is pretty much bereft of life, because there aren't enough resources to sustain plankton populations. However, every so often the Earth will slightly wobble on its axis - this is known as the Milankovitch cycle - and this has widespread climatic implications. The Earth begins to cool, the continents become more arid, and this in turn kicks up huge dust storms that, ultimately, end up in the Southern Ocean.
Those dust storms carry huge amounts of iron to the polar region, enough to jump-start the creation of massive amounts of plankton. These plankton get to work sucking up carbon dioxide, which is also crucial to keeping the planet cool over time. These iron deposits are enough to fuel entire Ice Ages, and you can probably see the possible application in today's warming world. Of course, we don't want to start dumping huge amounts of iron into the oceans unless we're pretty damn sure that it's going to work.
Now, thanks to research by Alfredo Martinez-Garcia of the Swiss Federal Institute of Technology, we have our most solid evidence yet. Analysis of marine cores taken from the southern Atlantic Ocean reveal that, going back four million years, dust levels are twice as high during periods of deep glaciation - in other words, during the Ice Ages - than they were normally. That's fairly compelling evidence that iron dust can have a major cooling effect on the planet's climate.
So far, we've done some minor experimentation with dumping iron filings into the ocean, but unfortunately we haven't produced anything more than some small plankton blooms. The issue may well be one of scale - this might be a solution that we have to commit to completely for it to work - and larger-scale experiments might now be in order. That's definitely risky, but at least it looks like the available evidence has tilted decidedly in its favor.