As unlikely as this may sound, we have lucked out in recent years when it comes to global warming.

The rise in the surface temperature of earth has been markedly slower over the last 15 years than in the 20 years before that. And that lull in warming has occurred even as greenhouse gases have accumulated in the atmosphere at a record pace.

The slowdown is a bit of a mystery to climate scientists. True, the basic theory that predicts a warming of the planet in response to human emissions does not suggest that warming should be smooth and continuous. To the contrary, in a climate system still dominated by natural variability, there is every reason to think the warming will proceed in fits and starts.

But given how much is riding on the scientific forecast, the practitioners of climate science would like to understand exactly what is going on. They admit that they do not, even though some potential mechanisms of the slowdown have been suggested. The situation highlights important gaps in our knowledge of the climate system, some of which cannot be closed until we get better measurements from high in space and from deep in the ocean.

As you might imagine, those dismissive of climate-change concerns have made much of this warming plateau. They typically argue that “global warming stopped 15 years ago” or some similar statement, and then assert that this disproves the whole notion that greenhouse gases are causing warming.