Finding the City That Holds Your Climate Future

Imagine, instead of trying to communicate the prospective climate change future, you could just time travel to experience the weather of 2050.

In place of having to convince the city engineers of Paris or Chicago to invest in better street drainage and passive-cooling architecture, you could take them to experience their city in thirty years, well within the lifetime of the facilities and infrastructure they are constructing today. Rather than having to factor in seemingly arbitrary modifiers to flood or heatwave risks, to stress test your future insurance losses, you could visit an insurer already experiencing and pricing those future climate extremes.

In evaluating climate, we already have an alternative to time travel – we can travel in latitude. You could accomplish all these tangible goals, if you could identify the place which today already experiences your future climate.    

In a study from the Departments of Environmental System Science and Environmental Engineering at ETH Zurich this potential has been unleashed on a global scale, across 520 major cities.   

Climate matching requires “fingerprinting” today’s climate and then using detailed modeling of future climate to search through the reference climate of all current cities to find the one which most closely resembles your own city’s future. In most cases, that 2050 future is a different city.   

Climate is characterized from temperature and precipitation data, not just yearly averages but the range of maxima and minima, sampled through monthly data using a total of 19 variables. In order to account for the correlation that exists among these variables, and to standardize their contributions to the climate fingerprinting of individual cities, in the ETH Zurich study a principal components analysis (PCA) was performed. Four principal components were found to account for more than 85 percent of the total variation of climate data and these four were then used for matching the cities.

A “middle ground” Representative Concentration Pathway (RCP 4.5) scenario was employed for the definition of future climate, which includes the assumption of a stabilization of radiative forcing before 2100. Three general circulation models (GCMs) were used to generate the 2050 climate data: two Community Earth System Models and the Earth System component of the U.K. Met Office Hadley Centre HadGEM2 model.  

The 520 major cities selected were either national or regional capitals or had a population in excess of a million. Among those selected the procedure then finds the best match: the city whose former climate was most comparable to the reference city in 2050.

For the Zurich study the climate data baseline was set as 1970-2000. This means we need to be careful when using the term “current climate”. We have already moved significantly off the end twentieth century baseline.  

European Cities Moving South

Across Europe, the 2050 cities are modeled to have a climate around ten degrees latitude south of their end twentieth century equivalents. Summers and winters grow warmer, with average temperature increases of 3.5 degrees Celsius and 4.7 degrees Celsius, respectively.

To find the climate of London in 2050 one should look to 1970-2000 Barcelona. Stockholm moves to Budapest; Moscow slides to Sofia.

In the western U.S., 2050 Portland becomes San Antonio, while San Francisco switches continents to become Lisbon. Northern mid-latitude cities show some of the largest shifts.  

For London, the climate is currently shifting south by an average of 20 kilometers each year. Take a climate change pilgrimage to the city you will become, a year in a day’s hiking.

Given that two decades have now passed since the baseline of this study, 2050 London is already two-fifths (or even half) the distance to Barcelona (according to whether the baseline average year is set at 2000 or 1985).

Everything is shifting. Today’s 2019 climate of Barcelona has already shifted from what it was between 1970 and 2000. Likewise, London’s climate has also warmed. Is Barcelona in 2019 no longer going to be the best exemplar of London in 2050? Is the climate of London 2050 more likely to be 2019 Montpellier or 2019 Lyon? This study does not explore the relativism.

While the transition to the climate of Barcelona may sound appealing, the shift does not stop in 2050 but continues as long as the causes of warming go unchecked. By 2060, London’s climate will have shifted further towards the equator. And for the Spanish cities themselves, the shift is far from favorable: the best match for 2050 Madrid is Marrakech 1970-2000, on the edge of the Sahara desert.

Closer to the equator lie many of the 22 percent of cities identified in the study that shift to climatologies without any current city equivalent. In Asia these cities include Kuala Lumpur, Jakarta, Rangoon, and Singapore, all shifting to steaming 2050 climates without precedent.

Identifying the cities that best match the future climate can help provide insights on what will happen to climate extremes. Like 2000 Barcelona, 2050 London can expect more droughts and heatwaves. Higher temperatures will lead to more intense rainfall events and flash floods, like those which flooded the Barcelona subway in 2011, and the streets in September and October 2018 and July 2019. The London city engineers should visit their counterparts to discover what will be required around water storage and urban drainage.

City matching to find the climate future, can help communicate what lies ahead at a local level. Yet such city matching cannot include the impacts of sea level rise or even the paths of intense cyclonic storms, more dependent on the pattern of regional thermal gradients and sea-surface temperatures.

Above all – change will be happening everywhere – there is no stable baseline. And building in anticipation of change is going to present an enormous challenge. Insurance will be left to pick up what falls through the numerous gaps in preparedness. Buildings, streets, drains, bridges, dams, tunnels have all been built to a climatology of rainfall extremes that has become historic, leaving the losses to become amplified. London underwriters should consider a trip to Barcelona to explore what lies ahead.