It shouldn't be a surprise that ... If you mess around in a big way with something that is really complicated, and has evolved over (at least) millions of year

It shouldn't be a surprise that ... If you mess around in a big way with something that is really complicated, and has evolved over (at least) millions of years, and there are so many factors that you are unable to take them all into account ... the consequences may not be predictable. The greenhouse effect, however, is quite easy to establish. Perhaps it's time to stop experimenting, for a century or ten.