Unsettled Science Knowrng that weather forecasts are rellable for a few days at best. we should recognlze the enormous challenge facrng seekrng to predtct clrmate change and Its Impact overthe next century In sprte of everyOrte's desrre fOr Clear answers rt Is not sur? that fundamental gaps tn knowledge leave unable to make reltable about future changes A recent report from the Nattonal Research Counc? (NRC) ralses Important Issues. Includrng these guestrons (1) Has human ac- thIty already begun to change temperature and the cttmate. and (2) How future change be? The NRC report 75 that Earth's surface temperature 77 has rtsen by about 1 degree Fahrenhelt over the past 150 years Some use result to clatm that humans are causrng 74 global andthey pornt to 73 storms or floods to say that dan- gerous Impacts are already under way Yet rematn unable to con?rm either contentton Geologlcal ewdence tndt- Sargasso Sea Temperature . of"? Moreover. computer models relted upon by cllmate predrct that lower atmosphenc temperatures nse as fast as or faster than temper- atures at the surface However. only the last 20 years have reliable global measurements of tempera tures In the lower atmosphere been available thr0ugh the use of satellite technology These measurements Show Ilttle If any Even less IS known about the potenttal 0r negatrve Impacts of climate change In fact. many academrc studtes and ?eld expenments have demonstrated that Increased levels of carbon droxrde can promote crop and forest growth So, whrle some argue that the scrence debate IS set- tled and governments sh0uld focus only on near-term poll? ores?that ls empty rhetonc lnevttably. future re- search help us understand how human actlons and natural clrmate change may affect the world and help determtne what acttons may be desrrable to address the long-term .: -. gets-?w a a: . cates that cllmate and green- house gas levels experience natural for reasons havrng noth- to do human Htstoncal rec0rds and current evldence show that Europe and North Amerlca expenenced a medieval warm perlod one thousand years ago. followed centunes later by a We we age The geological record shows even larger changes throughout Earth's hrstory Agalnst backdrop of large poorly understood natural vanabll- rty. rt tS for to the recent small surface temperature Inorease to human causes Serence has gtven us enough Information to know that cltmate changes may pose long-term risks Natural and human may lead to mate change that could be and perhaps both and negatlve Consequently. people. companles and QOvernments should take responsbte actlons now to address the Issue One essentlal step rs to encourage develop- ment of technologtes to meet Our fu- ture needs for energy We'll next look at the promlse of technology and what IS belng done today ExonMobil" EXXON corn t" . tn Fuu 1 Mom Corpon'tmt