The United Kingdom had its stormiest December for 50 years last month, with harsh winds, downpours and flooding that extended into the new year. Across the Atlantic, North Americans found themselves hunkering indoors — or stuck in airports — as a mass of Arctic air delivered snow and record low temperatures that brought services to a halt. As tends to happen whenever the weather goes haywire, many wondered whether larger forces were at work; British Prime Minister David Cameron said he suspected that global warming was partly to blame for his country’s suffering. It is a natural assumption, and scientists are actively engaging with the issue. But, as always, a little caution is in order.

On some level, most people understand the difference between climate and weather. Climate is the context: the accumulation of temperatures and precipitation trends that vary depending on location and season. Weather is what we experience, and extremes are part of the package. This was the message delivered by the UK Met Office, which pointed out that stormy conditions are more likely during winter months. Despite such assessments, however, people continually confound weather and climate in the heat — or cold — of the moment. Confusion seems unavoidable.

There are many ways to estimate the climate’s likely response to greenhouse gases, and the evidence cuts both ways.

In the United States, the cold snap extended as far south as Florida, forcing thousands of flight cancellations at the height of the holiday season. Climate sceptics celebrated, apparently unable or unwilling to accept that even a warming planet experiences cold temperatures. A small cohort of scientists countered with arguments that global warming might in fact be contributing to the string of abnormally cold US winters in recent years. The argument is that rapid Arctic warming and melting sea ice are destabilizing the fast-flowing air current known as the polar jet stream, leading it to the kind of drunken meandering that can push Arctic air across North America — and deliver powerful storms to the United Kingdom. If that is true, Cameron may well have been right.

Evidence for the claim that global warming could be disrupting the jet stream is disputed. Similar weather events have happened in the past, and at least one review of the record suggests that nothing is amiss — at least nothing that scientists can pin down as obviously outside the normal year-to-year seasonal variations. This does not mean that climate change has no role, of course. It just means that we do not yet know. In the words of one climate modeller, until the models and the observations align, we ought to reserve judgement. As far as the public is concerned, there is little to do but dress appropriately, keep an open mind and let the science play out.

The same dynamic has been playing out in recent years with regard to the average global temperature, which has plateaued since 1998. At first blush, the global-warming ‘hiatus’ runs counter to the warming projected by climate models. Here again, climate sceptics have pounced, and some climate scientists have rightly begun to explore both the climate system and their models to sort out the apparent discrepancy. As reported on page 276, researchers are homing in on a potential explanation that ties the periodic warming and cooling of the eastern equatorial Pacific Ocean to global temperature trends. In particular, the cool phase of the Pacific Decadal Oscillation — which took hold in 1998, coinciding precisely with the hiatus — seems to drive heat into the ocean, effectively cooling the atmosphere.

Plenty of questions remain. According to this theory, temperatures will rise anew when the eastern Pacific flips into its warm phase in the coming years. But how much warming should we expect when that happens? Exactly how sensitive is Earth’s climate system to increasing atmospheric levels of greenhouse gases? Some have argued, in part on the basis of current temperature trends, that climate models tend to overestimate warming, which would be good news indeed if true. But there are many ways to estimate the climate’s likely response to greenhouse gases, and the evidence cuts both ways.

Ultimately, the hiatus has provided an opportunity to better understand both the climate system and climate models. One lesson is that the climate, like day-to-day weather, has its ups and downs. Another is that the average global temperature — although a useful indicator — is not the only measure of how the climate changes. Scientists are still trying to work out what all of this means for the future, but if the past is any indication, we may have to live with a fair degree of uncertainty. From a policy perspective, little has changed. The range of potential impacts projected by climate models warrants much more aggressive action than has been initiated so far.