What does the counds of natural variaion mean?
The fact that the earth’s mean surface temperature has risen over the past century is not disputed. However, there are some that dispute that anthropogenic emissions have been the main cause of the observed warming. The climate change skeptics argue that the observed warming is still within the bounds of natural variation and, furthermore, that even if humans do contribute to global warming, the climate impacts are likely to be small and would not warrant the introduction of costly measures to reduce emissions

...is still within the bounds of natural variation..

What does the counds of natural variaion mean?

Question

What does the counds of natural variaion mean?
The fact that the earth’s mean surface temperature has risen over the past century is not disputed. However, there are some that dispute that anthropogenic emissions have been the main cause of the observed warming. The climate change skeptics argue that the observed warming is still within the bounds of natural variation and, furthermore, that even if humans do contribute to global warming, the climate impacts are likely to be small and would not warrant the introduction of costly measures to reduce emissions

...is still within the bounds of natural variation..

What does the counds of natural variaion mean?

Answer

"bounds of natural variation"

Let's look at it another way.

If you ask the question, "How tall are healthy adult humans?"

This cannot be answered with a simple number like 6 feet.  
There is a lot of natural variation in the height of adult humans.

So you could say that any height, from 4'10" to 6'10" (I'm just using an example, not scientific fact), would be within the "bounds of natural variation" of the height of adult humans.

I hope this is helpful.

Answer

Natural variation in this context is the temperature going up and down normally.

Bounds is another word for limit, so the bounds of natural variation means the change happening within normal limits.

Therefore, saying that "warming is still within the bounds of natural variation" means that the warming is not significant and a normal occurrence.

Does this answer your question?

Answer

bounds= "edges" or "limits" or "parameters"
natural variation= the normal changes in the Earth's temperatures