Consider this:

Humanity existed for over 200,000 years, hunting and gathering, before agriculture began. It became well-established on the order of 10,000 years ago, shortly after an unprecedented stability of the Earth's climate began as well (global average temperature varying only 3 degrees F for 10,000 years) .. That is not a coincidence. The stable climate has allowed humanity to continue to farm and its population to increase to over 7 billion (that's a problem, but another discussion).

Climate change will kick the Earth out of this unusual equilibrium and return it to the wild temperature swings it used to experience (global average temperature varying as much as 20 degrees F, sometimes within a few decades), This instability would lead to crop failures and make reliable intensive agriculture unreliable, thus making a population anywhere near its current level virtually impossible. We will not be able to "adapt" to the changes, unless "we" constitutes a total population much smaller than today's.