The National Climate Assessment, an extraordinary report published in November by 13 federal agencies and the White House at the end of last month, has shown that climate change has already had devastating effects on our health and economy and that costs could rise hundreds of billions of dollars by the end of the century.
The report illustrates what we can expect if we break down GHG emissions aggressively now and what would happen if we did not do anything. As part of our Weather 2050 project, we used this last scenario to examine what could happen at the temperature and precipitation in US cities by the middle of the century.
We have found that by 2050 many US cities could resemble the warmer and southernmost parts of the country today. We have mapped some of the most amazing transitions here:
As you can see on this map, climate change means that cities could move further south in terms of temperature and precipitation. In some cases, the nearest game may be hundreds of kilometers away. If you want to have an idea of what climate change could mean for your city, you may have to take a trip.
By 2050, in Cleveland, Ohio, the average summer peak warms by 5.4 ° C. The average winter minimum will increase by 5.3 ° F. This means that Cleveland will have the climate of a suburb of St. Louis more than 500 miles away.
Let us examine the way in which the climate in different regions could change. Take a look at this animation of changes in the northeastern United States:
You can see that Scranton, Pennsylvania, will have a climate that resembles that of Round Hill, Virginia, today. This is a distance of about 220 miles in the air line, but it means that Scranton will tackle average summer peaks that are 4.8 ° F higher and low winter temperatures that are 5.5 ° F higher.
We can also see it in the southeastern United States:
The cities of the South are moving further south. By 2050, annual temperatures and rainfall in Atlanta, Georgia, are more like Selmont, Alabama, today. It is a move of over 200 miles, with an average summer jump of 4.1 ° C to 92.6 ° F.
Other parts of the country may see smaller movements by 2050, as you can see in this map of the South-West:  Apache Junction, Arizona, will probably live in an all-year-round climate that is more like Peoria, Arizona, a city just 50 miles west. But this still means that the average summer peak from today, 103.5 ° F, will rise by 4.9 ° F by 2050.
As you can imagine, the shifts will be even higher by 2080. And in February (two months after this story was first published), two scientists unveiled in Nature Communications a new climate-analog mapping project for the United States showing that by 2080 the "climate of most of urban areas will move considerably and will become more like contemporary climates hundreds of miles away and especially to the south or will have no modern equivalents. "Play with their fascinating interactive here.
What climate change means for the United States
For each city, a few more degrees of heat and a few drops more or less rain in a season may not seem like much. But it can be the difference between having enough rain for healthy crops and a drought that kills them. It is the difference between wet winter and white winter.
Not all parts of the country are changing at the same rate. In general, the northernmost parts of the United States are warming faster than the southern ones, so climate change tends to be wider. Cities in the eastern United States and the upper Midwest are likely to see greater changes than the western ones.
But it is clear that hundreds of cities will have to adapt to changes that could be very profound for people's lifestyle. More homes will need air conditioners because the summers are filled with deadly heat waves. More vegetation will dry out, creating more fuel for fires. This in turn could influence the local economy as climate-dependent industries such as agriculture or the decline of open tourism.
It is important to note that the averages we quote do not tell the whole story. Some of the more temperate parts of the United States, like the Californian coast, will see more pronounced fluctuations in their climate. Rather than spreading rainfall throughout the year, California should see periods of intense rainfall followed by extreme dryness, a phenomenon that researchers have described as a meteoric whiplash.
The planet as a whole has already heated by 1 ° C since the dawn of the industrial revolution, and we are currently on track to see the 2 ° C warming by 2040. But we still have the opportunity to prevent the worst scenarios. And we already know what to focus on. Here is 10 ways to accelerate progress against climate change and a simple guide to climate policies that work.
How we made these maps
We have generated our city pairs by combining future annual temperature and precipitation projections to climate models throughout the year, looking for more present and future cities that are more aligned.
To build our comparisons, we calculated a minimum and maximum daily average of temperatures and rainfall for each month over 30 years (1986 to 2015) to establish a climate base for cities. Then we saw how these cities would have overheated by 2050, re-averaging over 30 years (from 2036 to 2065).
These projections are based on a series of climate models aggregated in the Localized Constructed Analogs dataset developed by the Scripps Institution of Oceanography at the University of California at San Diego.
The scenario here is built on a standard set of hypotheses in climate models known as CPR 8.5. This is generally seen as a high-end warming estimate since it assumes that the world will continue on the same course of carbon dioxide emissions with limited improvements in technology or efficiency.
That said, it follows closely where we are now and serves as a useful upper limit for what we can expect. CPR 8.5 also does not make a big difference in climate change estimates compared to other scenarios by looking at the middle of the century. The major variations under CPR 8.5 emerge around 2100.
There are many important caveats for our analysis. Part of the reason why we are not seeing major geographical changes in similar cities in the south is that we do not have enough cities available even further south for comparison. Our dataset includes only the continental United States, but a city in Texas could see its climate more like a city in Mexico, and a city in Florida could look like an island in the Caribbean. So there were many cities in the south for which we have no correspondence. We have chosen the best matches available with the data we have.
We are also comparing only cities based on temperature and precipitation, observing which cities today look more like those of a given city by 2050. These are just two dozens of variables that define a local climate. In addition, temperature projections in the middle of the century tend to be more robust than precipitation models, which are much more dependent on local variables and are more uncertain.
However, the greatest uncertainty here is the same as all climate predictions: how quickly will we act on climate change? If the world moves to a cleaner energy, it eats less meat, manages the land better, takes carbon dioxide out of the air, or sticks to business as usual will mean a huge degree of future heating.
What we do from now on is really important for our city, our country and future generations all over the world.