As the effects of human-caused climate change ramp up (think: record-breaking temperatures, extreme weather, and recently, a UN report revealing climate crisis disasters take place once a week), warnings from the scientific community are becoming ever more urgent.
Last year, an IPCC report described the catastrophic consequences of allowing average global temperatures to exceed 1.5°C warming above pre-industrial levels – but it can be hard to imagine what a world in which we fail to do so actually looks like. And that is where a new paper published in PLOS ONE conducted by scientists at the Crowther Lab at ETH Zurich, Switzerland, comes in.
Researchers used an "optimistic" climate scenario (more on that later) to pair 520 cities with a "counterpart" whose 2019 climate best matches their (predicted) 2050 climate. So that tomorrow's Madrid becomes today's Fez and 2050 Stockholm looks like 2019 Budapest. Meanwhile, the next 30 years will see Seattle look more San Francisco and the infamously gray London become hot and sunny like Barcelona. (You can find out the predicted climate of your city with this interactive map.)
The team chose to concentrate on cities because that is where more than 50 percent of the global population currently lives. To find out how they might change by the middle of the century, the researchers used 19 measurements, including yearly averages, seasonality metrics, and monthly precipitation and temperature extremes.
Climate change is a notoriously difficult thing to predict simply thanks to the sheer number of variables, from feedback loops to human activity. But for the study, the team used an optimistic scenario assuming radiative forcing stabilizes before 2100 and new technologies allow us to reduce greenhouse gas emissions – simply put, it makes for a relatively conservative reading.
That is not to say the results are anything less than extreme, with 77 percent of cities studied predicted to experience "striking change" transforming their climate into one more similar to another. What's more, 22 percent are predicted to see climate conditions currently not experienced by any major city on Earth.
The general trend seems to be a move towards less temperature seasonability, higher maximal and minimal changes throughout the year, and higher precipitation seasonability (i.e. the wet seasons will be wetter and the dry seasons will be drier).
The most dramatic transformations will be to cities in the northern latitudes – Europe, for instance, will see average increases in summer and winter temperatures by 3.5°C and 4.7°C, respectively. The average northern city will experience temperatures similar to cities 1,000 kilometers (620 miles) further south. That is a downwards “velocity” of 20 kilometers (or 12 miles) per year.
Meanwhile, cities in the tropics will become drier, with increases in extreme rainfall (+5 percent during the wettest month) and drought (-14 percent during the driest month). In sum: expect to see more water shortages along the lines of Cape Town 2018 and Dehli 2019.
There is also a great deal of uncertainty as many cities in the tropics will experience climate conditions that are so far unprecedented. Manaus, Kuala Lumpur, Jakarta, and Singapore are among the 22 percent of cities (64 percent of which are located in the tropics) predicted to experience novel climate conditions. Outside the tropics, Reykjavik in Iceland, Montreal in Canada, Las Vegas, St Louis, and Washington DC (all US) are also expected to experience unprecedented climate conditions.
"These are environmental conditions that are not experienced anywhere on the planet at the moment," Tom Crowther, founder of the Crowther Lab, told The Guardian. "That means there will be new political challenges, new infrastructure challenges, that we have not faced before."
As well as hoping to illustrate the realities of climate change (and encourage action to reduce its effects), the team hopes the study will help facilitate efforts to mitigate and adapt to the changing climate.