The National Climate Data Center reported Monday that the January-September period is tied with 1998 for the warmest first nine months on record.
The agency said the average temperature for the period was 1.17 degrees above normal for records going back 131 years. For a full year the warmest on record was 2005.
The agency added that it has been the warmest January-September on record in the Northern Hemisphere and the second warmest in the Southern Hemisphere.
Steadily rising temperatures in recent decades have raised concerns among environmentalists and atmospheric scientists concerned that human-generated pollutants are contributing the a dangerous global warming.
National Climate Data Center