Our atmosphere now holds CO2 at a level of 400 parts per million and to get an idea of what the climate would be like we need to go back 2.5 million years or further to the Pliocene epoch as that was the last time we had CO2 at this level.
If you think that this scenario is improbable, travel to a place where the temperature is about 3C different from where you live, which would normally be about 1000 Klm (650miles) North or South, and look at the trees. They will be mostly different and they are suited to their region.
The big action with climate change is in the oceans, but here we are looking at the land and plant life and using trees as an example, we can anticipate how they will fare in the new climate.
The trees of the Pliocene period were similar, but different, to the trees of today and were adapted to the climate that went with it. Those trees had taken hundreds of thousands of years to evolve to match those conditions. The trees we have today are adapted to a CO2 level of 280 PPM and a climate 0.8C cooler than todays and are rapidly going into conditions 2C warmer and with dramatically changed rainfall conditions of either drought or flood.