The key is that they're using reliable data collected over a century for their modeling, and they aren't trying to make Big-A projections from Big-A assumptions about data derived from sources whose accuracy and error ranges are impossible to calculate accurately. Their modeling is limited in scope to trying to understand the chemistry of our atmosphere and how that chemistry is affected by solar activity.
As I try and explain to people all the time - our atmosphere's chemistry is so poorly understood that climate prediction models in favor of global warming that use human carbon emissions as the cause are based on a simplified model that has the conclusion of carbon emission based global warming built-in to the model. In other words, the models are fixed to produce the predicted result.
Where has the Global Warming gone?
Long time passing;
Where has the Global Warming Gone?
Long time ago;
Where has the Global Warming Gone?
Vanish’d with the spots on our old Sun;
When will we ever learn?
When will we ever learn?