Climate is always changing.

During our planet's history, the climate has warmed so much that oceans have risen and covered much of the surface, or cooled so that giant sheets of ice have covered parts of North America and Europe (ice ages). These shifts in climate were dramatic, but they were also slow, occuring over thousands of years.

Most scientists think the last ice age, which consisted of four major glaciations, ended about 10,000 years ago. (Here's more about the most recent ice age. And some information about why ice ages happen.)

Many people think we're actually in an interglacial period, or a warm period in between colder ones. Here's a passage from a BBC feature on the ice age:

"Within an ice epoch there are ice ages, which alternate with shorter warmer periods known as interglacials. At the moment the Earth is passing through an interglacial period. This has lasted for around 10,000 years following the last Ice Age, which in turn went on for some 100,000 years. It would appear from historical climatic evidence that this ice age/interglacial pattern was established at the beginning of this ice epoch. Perhaps ominously for man, the pattern suggests that ice ages last around 100,000 years on average and the shorter, warmer interglacials around 10,000 - so we are nearing the end of our current warmer period.

However, there is no need for any alarm at this thought. The next ice age could be up to 1,000 years or more away - a short period in climatology but a comfortingly lengthy one for us. And in any case no one can yet predict what effect the greenhouse effect may have on the overall pattern of global cooling and in arresting a return to glacial conditions.

What does seem apparent is that within the current interglacial period, starting some 10,000 years ago, there have been smaller patterns emerging - periods of warmer weather, followed by colder weather and so on. These have been broken down by climatologists into four main periods.

The first followed the end of the last Ice Age, indeed it caused it to end. The Earth probably reached its warmest about 5,000 or 6,000 years ago. At this time the temperature would have been on average about 2C (3.6F) warmer than the present day."

But that doesn't let humans off the hook, unfortunately. Some of the warming trend we're seeing may be natural, it's true. But the scientific consensus is that the greenhouse gasses that people produce are a big part of it. In the last hundred years, the Earth has warmed by about 1°F. That's a really fast change, geologically speaking. Rising temperatures and melting glaciers have already caused sea level to rise 6-8 inches worldwide. While there is scientific debate about how much change we're causing, what's likely to happen, and how quickly, there's really no question that humans are having an impact

The National Academy of Sciences has a web section devoted to issues of global climate change.

Check out the full Science Buzz feature on global warming.

I completely agree. If it had been getting colder, people would probably think that global cooling existed! the temperatures change, and it is not our fault!