The 4th IPCC report came out in 2007 but it took some years to write. In turn, it depended on peer reviewed studies that themselves took time to research and write.
So the 4th IPCC report is based on the most solid data in the world, but it is getting a little old in a rapidly evolving field.
Many papers have been produced in the meantime and we can expect, as we’ve seen in each successive IPCC report, that the 5th report will be even more worrisome.
One of the biggies not taken into account are studies concerning enormous deposits of frozen methane in the arctic and in the sea bed. As the planet warms the fear is that these will thaw and bubble up to add significantly to the warming effect of CO2—this is called a feedback.
There are others.
The big fear is of passing a point of no return where no matter if we stop burning fossil fuels, climate change takes on a life of its own and keeps getting hotter and hotter anyway.
The temperature at which we pass this dangerous tipping point isn’t known but international hope is that at 2°C we’ll still be okay.
But studies since 2007 forecast 5°C and 6°C rises this century.
Other studies predict that this means that many agricultural regions will be plagued by drought and become dust bowls. Then there are studies about food security, health impacts, extreme weather, and more.
These aren’t the claims of environmental activists. These are peer reviewed scientific papers.