chicago underneath downtown chicagos soaring art deco towers its multilevel roadways and its busy subway and rail lines the land is sinking and not only for the reasons you might expectsince the mid20th century the ground between the city surface and the bedrock has warmed by 56 degrees fahrenheit on average according to a new study out of northwestern university all that heat which comes mostly from basements and other underground structures has caused the layers of sand clay and rock beneath some buildings to subside or swell by several millimeters over the decades enough to worsen cracks and defects in walls and foundationsall around you you have heat sources said the studys author alessandro f rotta loria walking with a backpack through millennium station a commuter rail terminal underneath the citys loop district these are things that people dont see so its like they dont existit isnt just chicago in big cities worldwide humans burning of fossil fuels is raising the mercury at the surface but heat is also pouring out of basements parking garages train tunnels pipes sewers and electrical cables and into the surrounding earth a phenomenon that scientists have taken to calling underground climate changerising underground temperatures lead to warmer subway tunnels which can cause overheated tracks and steambath conditions for commuters and over time they cause tiny shifts in the ground beneath buildings which can induce structural strain whose effects arent noticeable for a long time until suddenly they aretoday youre not seeing that problem said asal bidarmaghz a senior lecturer in geotechnical engineering at the university of new south wales in australia but in the next 100 years there is a problem and if we just sit for the next 100 years and wait 100 years to solve it then that would be a massive problembidarmaghz has studied subterranean heat in london but wasnt involved in the research in chicagoto assess underground climate change in chicago rotta loria an assistant professor of civil and environmental engineering at northwestern has installed more than 150 temperature sensors above and below the surface of the loop he combined three years of readings from these sensors with a detailed computer model of the districts basements tunnels and other structures to simulate how the ground at different depths has warmed between 1951 and now and how it will warm from now through 2051near some heat sources the ground beneath chicagoans feet has warmed by 27 degrees fahrenheit over the past seven decades he found this has caused the earthen layers to expand or contract by as much as half an inch under some buildingsthe warming and ground deformation are now happening more slowly than in the 20th century he found simply because the earth is closer to being just as warm as the basements and tunnels buried within it more and more those structures will stay warm rather than dissipating heat into the ground around themrotta lorias findings were published tuesday in the journal communications engineeringthe most effective way