In the absence of a time machine, it is difficult to understand what will be the future climate. The climate projections figures contain a lot of information, but these figures may seem abstract – what do you actually feel at 2.5ºC?
One way to understand this information is to get in the car (even if it's not a DeLorean). There is a wide variety of local climates around the world, and it is possible to find a location aujourd & # 39; hui it should look a lot like what your home town will want in a few decades. A new study by Matt Fitzpatrick and Rob Dunn applies this "analog climate" approach to 540 cities in the United States and Canada – meaning that about 250 million people can use a web map to look for an analogue in the United States. climate of their future.
Present and future climates
You can imagine defining such a comparison in several ways. In this case, the researchers disaggregated the data by season by calculating minimum / maximum temperatures and average total precipitation over the period 1960-1990. This is basically the seasonal time you are used to.
To see what future climate change should bring, researchers measured the results of 27 different climate models. For each point located around North and Central America, they calculated seasonal temperatures and precipitation for 2070-2099. This has been done for two scenarios of greenhouse gas emissions: a high-emissions scenario where nothing is done to reduce emissions and a medium-emissions scenario that would stop warming by a few degrees more early.
The researchers then analyzed the models for each current city at a point where future climate variables were very close. For the purpose of the web map, they choose the closest match possible, even if it does not meet their statistical threshold of good analogues. (There is an option to display the degree of similarity on the map.)
In general, global warming means you have to head south to find your analog climate. Portland, Maine, for example, would have a climate similar to that of Baltimore by the 2080s without reducing emissions – considerably warmer and wetter than the one Mainer is accustomed to. Beyond human expectations of time, you can think of the difference between climate-friendly ecosystems in these two regions.
Keep the distance
However, there are other factors to consider, such as elevation. High-altitude cities can find their analogue of the warmer future simply by getting closer to sea level. As a result, the match of some cities may even be theirs. North. And of course, comparisons are otherwise limited by what exists south of you. The coastal cities of Florida, for example, have no choice but to leap the gulf in Central America, which does not always give a good comparison.
Overall, the average analogue in the average emissions scenario results in a distance of more than 500 km (up to 850 km (530 miles) with higher emissions.) Northeast cities generally have to turn to the southwestern Midwest and wetter regions of the Southeast to find analog climates, while cities in the West must turn to the southwest, drier.
In the average emissions scenario, most cities have a close analogue that exceeds the statistical threshold. The only exception is the west and southeast coast, which has a more difficult time. However, in the high-emissions scenario, only 17% of cities can find a perfect match. The climate change is too important for you to easily find something similar. You must therefore relax your standards and settle for what is closest to you.
The other way of looking at things, as the researchers say, is that "if we continue on our current trajectory, the climate of many urban areas could become different from everything in the field of study, while now warming in the optics of the Paris Agreement could reduce the exposure of urban areas to climate change ".
Washington DC, for example, can find its analogue future in Paragould, Arkansas, for a medium-emission scenario. But if we do not reduce our emissions, the nearest analog (a poorer instrument) is in Greenwood, Mississippi. So, all the people in the District who love the Southern climate have a choice: they can settle in now or stay in place for a few decades and let the climate come to them.
Open Access to Nature Communications, 2019. DOI: 10.1038 / s41467-019-08540-3 (About DOIs).