Today's Emissions, Tomorrow's Warming

As the UN Climate Change Conference gets underway in Morocco, and the nations of the world work toward cutting greenhouse gas emissions, we examine how high temperatures throughout the year are projected to rise by the end of the century under two different emissions scenarios. Specifically, we examine the business-as-usual scenario (RCP 8.5) and a scenario with substantial greenhouse gas emission cuts (RCP 4.5) for each of our Climate Matters markets. Increasingly, it appears that the lower emissions scenario will be unlikely to limit warming to less than 2°C above pre-industrial levels.

Winters are already the fastest warming season through much of the U.S., and that trend is likely to accelerate in the coming decades, especially in colder climates. For Minneapolis, which currently has high temperatures below freezing for much of the winter, highs in the 30s will become more common by 2100. This means snowpack and frozen lakes will probably become less consistent, leading to less snowmobiling and ice fishing, and affecting the communities that depend on those activities for winter tourism.

Warmer states, such as Florida, will see their pleasant winters become more tropical. Winter highs in Miami are generally in the 70s, but by the end of the century, highs in the 80s will become the norm, so air conditioners could get a workout all year long.

Summers have not warmed as fast as winters in most places, but the additional warming will likely increase heat-related illnesses such as heat stroke. Summer days in Chicago, Detroit, and New York currently reach the 80s on average, but they will likely top out in the 90s more consistently by 2100. Las Vegas and Phoenix — already used to temperatures several degrees above 100°F during the summer — are likely to see average summer highs above 110°F.

With all the added heat, summers will be longer and more intense, as spring arrives earlier and fall starts later. And while winters will still be cold, most will be shorter and milder in the coming years.

Methodology: Historical weather station maximum temperature data was averaged by day for the period 1996-2015 to obtain the 2016 baseline. The mean maximum temperature projections for 2100 were derived from a suite of 28 climate models (CMIP5 / Oak Ridge National Laboratory), averaged by day for 2080-2099 under IPCC emissions scenarios RCP8.5 and RCP4.5.