You appear to be saying that you think this could be explained by some natural variation. That seems plausible, but is not supported by scientific evidence.
The term "man-made climate change" is a term for the truth of these three claims:
1. Human activity has increased the concentration of CO2 (and other green-house gases) in the atmosphere.
2. The global temperature has risen over the last 150 years.
3. An increase in the concentration of CO2 in the atmosphere is the cause of the rise in global temperature over the last 150 years.
Point 2 is simple scientific fact by now. Measurements show that this is the case, despite being critically revised and corrected for sampling biases over the years. Point 3 is also scientific fact; the theoretical effect has been shown to be true in simple laboratory expirements (it has been known for over 100 years) and the strong correlation of CO2 concentration and temperature over the last 150 years overwhelmingly implies that this laboratory effect applies for the atmosphere as well.
That could still mean that the source of all of this greenhouse gas is natural. Still seems plausible, but again scientific evidence shows that the large majority of this "new CO2" is sourced by human activity [1]. Various sources of evidence exist; the isotopic signature of CO2 in the atmosphere is atypical for natural sources, the concentration of CO2 in the oceans is rising fastest near the surface, and there are many more pieces of evidence.
It is true that there is still a large degree of ignorance on how global temperature varies "naturally" over long periods of time. However, we can show that this specific warming we're observing today is not just a natural variation. It is caused by humans.
The term "man-made climate change" is a term for the truth of these three claims:
1. Human activity has increased the concentration of CO2 (and other green-house gases) in the atmosphere.
2. The global temperature has risen over the last 150 years.
3. An increase in the concentration of CO2 in the atmosphere is the cause of the rise in global temperature over the last 150 years.
Point 2 is simple scientific fact by now. Measurements show that this is the case, despite being critically revised and corrected for sampling biases over the years. Point 3 is also scientific fact; the theoretical effect has been shown to be true in simple laboratory expirements (it has been known for over 100 years) and the strong correlation of CO2 concentration and temperature over the last 150 years overwhelmingly implies that this laboratory effect applies for the atmosphere as well.
That could still mean that the source of all of this greenhouse gas is natural. Still seems plausible, but again scientific evidence shows that the large majority of this "new CO2" is sourced by human activity [1]. Various sources of evidence exist; the isotopic signature of CO2 in the atmosphere is atypical for natural sources, the concentration of CO2 in the oceans is rising fastest near the surface, and there are many more pieces of evidence.
It is true that there is still a large degree of ignorance on how global temperature varies "naturally" over long periods of time. However, we can show that this specific warming we're observing today is not just a natural variation. It is caused by humans.
[1] http://www.skepticalscience.com/co2-increase-is-natural-not-...