Emily Elias: It’s getting colder and those Christmas lights are in full force. But the question remains, will the UK get one of those idyllic white Christmases that we usually see on Christmas cards? Or not so much? On this episode of the Oxford Sparks Big Questions Podcast, we are asking, with climate change in play, what are the odds of a white Christmas?

Hello, I’m Emily Elias, and this is the show where we seek out the brightest minds at the University of Oxford, and we ask them the big questions. And for this one, we have found a researcher who is willing to conjure up some holiday spirit and predictions.

Neven Fučkar: I’m Neven Fučkar. I am a climate and data scientist at Environmental Change Institute at the University of Oxford, and I work on a number of things. For example, I focus on extreme events, on their dynamics, prediction, attribution and socioeconomic impacts.

Emily: Okay, well, nothing could be more extreme than whether or not we will have a white Christmas. So, I mean, how far in advance do we know when we’ll have a white Christmas in our forecast?

Neven: Well, that depends on the precision that we are looking for. For example, if we really want to know whether it’s going to snow on Christmas, then unfortunately we will have to wait for the weather forecast initialised two to five or seven days before the Christmas. Because in this sense, we are able to actually know what will be the temperature on the Christmas day and what will be the probability of precipitation. So, this is typical weather forecast, which we are interested. We can even look it up at the practical valley up to ten days in advance.

Emily: Okay, so we can have a short range forecast that looks at the temperature and the precipitation. What about a long range forecast? How do we know what we can predict in a different sort of model where we’re looking from a bigger picture?

Neven: Sure. So, in practical sense, that can be the same models. But the way that we are approaching to information is we are looking at, how to say, high resolution, high precision forecast on a daily timescale. When we are talking about sub-seasonal or seasonal forecast, we are looking at predictions on timescales of two to twelve weeks, or for example, two months to twelve months. Then we are looking at the long term means. For example, when we are talking, of sub-seasonal forecast, we are talking about weekly average. Or if we are talking about seasonal forecast, then we are talking about monthly average or even seasonal average. So, we are going from understanding in weather forecast what’s going to happen on hourly timescales day by day. Now we are going into the predicting mean values over a certain period of time that are still very practical, you know. Understanding what would be the mean temperature during the week of Christmas still provide us with very actionable information.

Emily: So how far out can we know if it’s going to be a white Christmas? So, Christmas 2023, how many months in the past would I be able to sort of say with some certainty that it would be a white Christmas?

Neven: Today, weather forecast is typically between 80% to 90% accurate. So. two days in advance, we would know with very high skill and very high precision whether we’re going to have a white Christmas or not. But if you look at the two months, for example, out, that uncertainty is bigger but it still provide you with better understanding because if your entire week or entire month of the Christmas you have substantially warmer temperature conditions, the probability that you’re going to experience white Christmas is much, much smaller than average. So, it is always the further away we go, we have less certainty. We are dealing with probabilistic information, but that can be utilised and different users utilise it in different sense.

Emily: Okay, so you’re going to hate me. I’m going to go even further out. What if we could look at Christmas 2043, Christmas 2053, Christmas 2063. Do we know any sense of what climate change will happen and whether we’ll be more likely or less likely to have a white Christmas?

Neven: Well, in this case, when we are looking at further and further time horizons, we’re talking about five years, ten years and further, then we are going into the domain of climate projections. They depend on what kind of greenhouse gas emissions, aerosol emissions society will produce. But in the spectrum of possible future scenarios, typically United Kingdom, we are seeing warming of the winter months. There is no region in United Kingdom that will see potentially colder winter months, colder December, colder winter. In ten years or 20 years, we, are all experiencing increase in temperature, therefore decrease in probability of experiencing white Christmas. That doesn’t mean that white Christmas would be impossible, but it’s less likely.

Emily: So, extreme events that we would be dealing with would less likely be that it would be a snowy event and more likely it would be what, per se?

Neven: So, we would probably experience less cold waves, cold snaps. Temperature will be warmer. We might even experience some heat waves in the winter. But that’s all relative, relative to the long term mean, you know. The heat wave in summer you physically experience in July or something like when we cross or approach 40 degrees celsius. This is what we are, considering to be a heat wave with respect to long term means of the July. But in the winter, we can also experience strange heat waves, but in absolute sense, they would be not that memorable. But we will most likely experience increasing temperatures and what we expect that we’re going to experience more precipitation in the winter. So probability of a white Christmas in the future, next 10, 20 or 30 years is decreasing. And, what is increasing is probability of warm Christmas with just rain.

Emily: Okay, so less Dickensian, Victorian snow scenes on the Thames and people ice skating, more Santa at the beach wearing board shorts.

Neven: Yes, perhaps Australian Christmas type of them, but I hope not that hot. True, yes, those scenes about frozen Thames and fairs on ice, I would say that that is extremely unlikely because when you put it in historical context, those scenes and historical events took actually place during something that we called Little Ice Age. This is the period where Europe and some other parts of the world were actually experiencing colder conditions than normal, roughly between 1350 to 1850. So these are some of the coldest periods in last few thousand years. That is very unlikely that we’re going to experience that in the future.

Emily: Ok, so, focussing…. we are two weeks out from our Christmas 2023. Will it be a white Christmas? What is the science telling us?

Neven: Well, a number of operational institutions around the world, weather forecasting, government services, as well as academic groups, they are producing dynamical and statistical forecasts. And then you can combine them, analyse and calibrate them to get the best possible multi method, multimodal forecast. And at this stage, the most likely outcome is that we’re going to have a week of the Christmas warmer than average. And precipitation around the United Kingdom will be typically normal, except parts of the southeast and southwest should experience a little bit extra precipitation. But most likely there will be no significant snow.

Emily: So it’ll be Christmas jumper weather instead of Christmas jacket weather.

Neven: Yes, you can put it that way. However, I must put disclaimer, there is no guarantee we couldn’t have a surprise, because on top of the long term forced changes, we also have internal variability, but that will be less likely. The more likely outcome is a warm Christmas without snow.

Emily: Well, I hope however you celebrate Christmas, I hope you have a lovely one.

Neven: Thank you, Emily. Same to you.

Emily: This podcast was brought to you by Oxford Sparks from the University of Oxford, with music by John Lyons and a special thanks to Neven Fučkar. Tell us what you think about this podcast. We are on the internet @OxfordSparks and you can find our website at oxfordsparks.ox.ac.uk.

I’m Emily Elias. Bye for now and Merry Christmas.