What’s the difference between climate and weather?

One of the first things I get asked when I talk to school students is: “What’s the difference between weather and climate?”

The answer – that climate is the statistics of the weather – doesn’t bring a lot of excitement to the classroom, so I use an analogy from a friend at the Bureau of Meteorology: climate is what you expect; weather is what you get.

Climate is the wardrobe, but weather is what you pick out to wear on the day. You’d have a few pairs of shorts in your cupboard if you lived in Darwin or in Deniliquin. But only one cupboard would stock woolly jumpers too.

Taking the analogy one step further, we rarely notice other people’s wardrobes. But we do notice their outfits. You probably haven’t noticed the steady increase in Australia’s average temperature, which has risen from just over 21°C to almost 22.5°C in the past 60 years.

But you may well have noticed heatwaves becoming hotter and more frequent, an increase in 40°C days, and storms that pack more punch than they used to.

With longer sets of weather observations available to study, larger supercomputers, and people hungry to connect the daily forecast to climate change, more climate research is now turning away from the big picture averages, and looking at changes in our actual weather.

For example, 2019 was Australia’s hottest and driest year on record. The fingerprints of human-induced climate change are all over the ‘hottest’ part of that statistic, just as they have been every year since at least 1950.

But the role of a warmer planet on the ‘driest’ part is still being debated. So many remote factors affect whether or not we get rain: what’s going on in the Pacific Ocean, the Indian Ocean, the Southern Ocean – even the winds 10km above Antarctica can affect our climate in some way. This interconnectedness is the wonder of climate research, but it can make the stories of our droughts tricky to untangle.

Which is why it’s nice when studies look for something simple. Recent work from Acacia Pepler at the Bureau of Meteorology found we had a record low number of low pressure systems across southern Australia in 2019.

This research is not talking about ocean temperatures thousands of kilometres away, or summarising the rain gauges of an entire country using one bar on a graph. It’s talking about the big “L”s we see on the daily weather map, and the fact that there were fewer of them in 2019 than in any of the previous 50 years. The study doesn’t explicitly link the small number of lows to human-induced global warming, but it joins a number of studies finding a similar trend in past observations and models of the future.

Of course, it’s not just in synoptic maps that the link between weather and climate change is becoming clearer. Detecting a change in the behaviour of weather events and attributing this change to increased greenhouse gases (the field of detection and attribution) can now be done so quickly that rapid studies can be completed in a week or so. This allows researchers to answer another common question that gets asked: “Was that [enter recent disaster here] due to climate change?”

Being lovers of statistics, climate scientists prefer to rephrase the question as “how much more likely, or how much worse, was that recent disaster, thanks to the extra greenhouse gases in the atmosphere?”. For heatwaves, the answer is almost always “a lot”. Studies are now regularly finding that record-breaking temperatures are “virtually impossible” without human-induced climate change.

But we’re now starting to ask the question in another way. Instead of saying “how much worse was this recent event?”, an international team led by Tim Cowan, at the University of Southern Queensland, asked “how much worse would this historical event have been if it happened today”?

They studied the 1930s Dust Bowl drought in the US, which decimated crops across North America’s Great Plains, caused widespread dust storms, and was associated with scalding temperatures across the country. The summer of 1936 is still the hottest season ever recorded in continental North America.

By using over a thousand model versions of past and present climate, they found that increased greenhouse gases already played a role in the widespread dustbowl heat, even though it happened almost 90 years ago. They also calculated that dustbowl summers are twice as likely to happen now, and if they do happen, there will be at least an extra week of heatwave conditions.

What I appreciate about these new studies — the refocussing on the synoptic scale, the looking at the past with a climate change filter applied — is that they spark new kinds of conversations around climate change.

As much as it saddens me, most people aren’t too impressed by cupboards – I mean, statistics. They’re much more interested in what they’re going to wear today.

Some studies also suggest that for conservative thinkers, talking about the good old days may be more engaging than imagining the future when it comes to environmental action.

A few weeks ago, the Australian Academy of Science released a detailed report called The risks to Australia of a 3°C warmer world. It was designed to highlight how bad things will likely be at the end of this century if we fail to move purposefully towards zero-greenhouse-gas emissions. In the media however, it didn’t get much traction – possibly because it portrayed a future too bleak for most people to imagine.

But if we bring attention to changes in our weather maps, we make a tangible link between global climate change and what is happening right above our heads. And by looking at events that loom large in history and persist in the memories of many people, we can engage people with climate science through impacts they can connect to.

One other question I’m regularly asked is: “What can we do about it?” The Academy of Science report highlighted that there are a lot of things that need to happen very quickly. If we can engage as many people as possible in conversations around climate change, and to do that in a way that doesn’t prompt them to ‘switch off’, we activate a simple and powerful way to help turn questions into action.