Free Astronomy Magazine November-December 2020

32 NOVEMBER-DECEMBER 2020 ATMOSPHERIC POLLUTION can be found trapped in glaciers. This is perhaps because, between 250 B.C. and 400 A.D., the European continent went through a phase with an unusu- ally warm climate, known in history as the “Roman Warm Period.” Nonethe- less, it is likely that for some centuries the atmosphere had shown anom- alous abundances of lead and anhy- drides. But even if this were not the case, there is certainly another indica- tor that may have signaled our pres- ence to other civilizations at that same time: methane. Forest conversion for agriculture and livestock in the Roman Empire, to- gether with the simultaneous large expansion in China of areas cultivated for rice harvesting under the Han dy- nasty, started a forced increase in the abundance of methane in the atmos- phere. A study conducted in 2012 by a team of European and American re- searchers on ice cores extracted as part of the North Greenland Eemian Ice Drilling (NEEM) project showed that, precisely at the developmental peak of those ancient civilizations, signifi- cant quantities of greenhouse gases were produced, among which meth- ane stands out. Célia Julia Sapart, a specialist in greenhouse gas emissions and historical climate reconstruction, as well as the leader of the team that conducted the study, said that “the ice core data show that as far back as the time of the Roman Empire, human activities emitted enough methane gas to have had an impact on the methane signature of the entire at- mosphere,” hence globally. Since all this happened almost 2000 years ago, the anthropogenic mes- sage carried by the light reflected from the Earth has reached (over the centuries) all the stars up to almost 2000 light years away, which are es- timated to be about 50 million. Ac- cording to new estimates (June 2020) by astronomers at the University of O n this page, some snap- shots of the North Greenland Eemian Ice Drilling, the project that has given to numer- ous groups of re- searchers the opportunity to study variations in climate and at- mospheric com- position. [NEEM Project Office]