Quote:
Originally Posted by chrisrushton  It's true that the sun works in cycles but the fluctuations in global temperatures measured (for example) in ice cores over the course of the earth's "life" are small compared to what we have seen over the last 50 or so years. |
According to ice core data, the earth's global temperatures have been higher than today's temperatures in at least 4 periods within the last 500,000 years. (See
http://www.sierraclub.ca/national/pr...k-ice-core.jpg)
The number that has increased in recent times is CO2 concentration in the atmosphere, which is currently about 25% higher than it ever has been (370ppm in 2002 vs. ~300ppm 320,000 years ago). As someone else already pointed out, CO2 changes are a natural effect of temperature fluctuation, not the other way around. While you are correct that we would "end up like Venus" if CO2 continues to increase, we certainly have a LONG way to go.
The atmosphere of Venus is
960,000ppm (96%) versus our current
370ppm (0.37%). Human emissions have contributed to just 70ppm (0.07%) increase in the concentration of CO2 in our atmosphere over natural limits.