A back of the envelope, fact-based prediction if mankind doesn't get its shit together.

Global CO2 levels currently stand at roughly, 400 PPM (parts per million). That's an increase of 100PPM over the last 50 years.

During the Cretaceous Thermal Maximum the CO2 concentration was over 1000PPM. At this time, due to the heat, the Earth had tropical oceans at the poles.

If we don't slow down the release of CO2 and the rate of release DOESN'T increase....which it probably will given China and India's planned energy production capacity increases, then in 300 years were looking at a rise of 600PPM - which brings us dangerously close to the CTM.

Which is a world with tropical oceans at the Poles and inhuman temperatures around the Equator.

Bare in mind that the CTM was a (relatively) gradual development and flora and fauna had thousands (if not millions) of years to evolve and adapt to the gradual increase in global temperatures.

Such a temperature change over 300 years would kill most local ecological biomes. It would be a mass extinction event.

So a much warmer earth. With considerably fewer species. If there is space for humans, then there won't be much space. Food will be hard to grow once all the natural pollinators have died off.

Of course, it doesn't have to be this way....and we could stop this future in its tracks if we all forced our politicians to pull their heads out of their arses. So their is hope -but that depends on everyone pushing for change.