The author which wrote the “conclusion” as you named it wrote on the same site a personal note:
“That very uncertainty is part of what, I am confident, is known beyond doubt — our planet's climate can change, tremendously and unpredictably. Beyond that we can conclude (with the Intergovernmental Panel on Climate Change in its 2007 report) that it is very likely that significant global warming is coming in our lifetimes. This surely brings a likelihood of harm, widespread and grave (see this summary of expected impacts). The few who contest these facts are either ignorant, or so committed to their viewpoint that they will seize on any excuse to deny the danger.”
So it’s not “exact” in a sense to give you precise temperature values for every day, but it’s known beyond doubt that it’s very dangerous and that we should take action now.