During the 20th century, pollution has become a problem former centuries scarcely knew Until recently no one thought that human actions could affect the world on a global scale, says National Geographic
आता काही शास्त्रज्ञांची अशी खात्री पटली आहे की, लिखित इतिहासात पहिल्यांदाच अशाप्रकारचे बदल घडत आहेत. ”