File:This graph shows Global Average Temperature between 1880-2009 compared with the Atlantic Multi-decadal Oscillation (AMO) Index. The roughly parallel curves of the two parameters show that they are related.gif

English: Description is based on an edited quote of the cited public-domain source: This image shows a graph of global average temperature between 1880 and 2009 compared with the Atlantic Multi-decadal Oscillation (AMO) Index. The AMO Index is the average sea-surface temperature over the North Atlantic Ocean. The roughly parallel curves of the two parameters show that they are related: the increase in global temperature over time, coincident with the increase in greenhouse gases observed since the Industrial Revolution, is alternately obscured and enhanced by the AMO.

The AMO transports a large amount of heat during its cycle, which takes around 65 to 70 years. Over that time, the amount of heat moved northward along the western side of the North Atlantic Ocean oscillates, increasing and decreasing temperatures in the North Atlantic Ocean and the surrounding continental margins. The AMO's transport of heat helps explain some counterintuitive temperature trends during the twentieth century. Despite the increase in greenhouse gas concentrations that began in the mid-1800s, between 1850 and 1900, global temperatures showed little significant change. Between 1900 and 1940, temperatures rose. After 1940, temperatures declined for 35 years. The lack of a direct correlation between greenhouse gas concentration and global temperature over this time span “was confounding understanding of the observed temperature record,” recalls Michael Schlesinger (University of Illinois at Urbana-Champaign), “and it was allowing people to make the argument, ‘If there was this early twentieth-century warming when humanity was putting relatively fewer greenhouse gases into the atmosphere, why wasn’t there a larger temperature increase later when humanity was putting vastly more greenhouse gases into the atmosphere?’ By discovering this oscillation, we were able to refute this argument.”

Attribution of recent climate change has further information on attributing recent climate change to human activities.