Global warming in the industrial age is “ unprecedented ” in the past 2,000 years , with human activity “ unparalleled ” in its impact on absolute temperatures , according to a study published in Nature . 32, L23711 (2005). It found no evidence of globally coherent cold and warm periods in the pre - industrial era , when the lowest temperatures were found in sporadic periods during the fifteenth , seventeenth and mid - nineteenth centuries . In contrast , the warmest period of the past 1000 years occurred during the twentieth century over more than 90 % of the planet .
Global warming in the industrial age is “ unprecedented ” in the past 2,000 years , with human activity “ unparalleled ” in its impact on absolute temperatures , according to a study published in Nature . It found no evidence of globally coherent cold and warm periods in the pre - industrial era , when the lowest temperatures were found in sporadic periods during the fifteenth , seventeenth and mid - nineteenth centuries . In contrast , the warmest period of the past 1000 years occurred during the twentieth century over more than 90 % of the planet .