If we burn fuels which create excessive amounts of carbon particulates then this had the effect of reflecting sunlight and heat back into space, as it acts as a kind of insulator.
When Krakatoa went pop in the 19th Century, there were vaired reports of crimson skies at dawn and dusk, accompanied by a significant drop in average global temperatures which led to several crop failures.
This was because of the amount of dust ejected into the atmosphere, reflecting a significant percentage of solar radiation back into space, cooling the atmosphere of the planet and leading to all kinds of meteoroligical shenanigans. It's also the principle behind the "nuclear winter" theory.
Right now we have a sharp rise in greenhouse gas emissions within the last century. This is accompanied by unprecedented particulate emissions (carbon particles make great solar reflectors) hence the problem.
Solution? If we stop emitting carbon tomorrow then the greenhouse effect might accelerate. If we stop emitting CO2 tomorrow then global cooling might accelerate.
There's so much we don't know. Our weather patterns are finely balanced and are co-dependant on so many factors that we can't produce an accurate model of climate change yet. The sun is behaving oddly of late (solar radiation is increased), the ocean's plankton which process more CO2 than all the rainforests in the world put together is in decline, rainforests themselves are being cut back and we're emitting greenhouse gasses from industry, domestic heating, air travel, power generation and road/rail transport. New Zealand is even introducing a "Fart Tax" on livestock farming to counter methane/Co2 emissions, but we aren't addressing the issues quickly enough.
