If you look at the graph of the last century the global temperature, eyes rush failure in 1960. Over this period, said a lot of cool. Some point to fluctuations in emissions of aerosols (small particles), which reflect sunlight. Others nod to the Atlantic Ocean circulation, which is called the cycle of changes multidekadnoy Atlantic Oscillation (AMO). The situation is complicated by the fact that the former can affect the second, and the accumulated effect of both.
Surface waters that flow into the North Atlantic, cool, approaching Arctic sink into the abyss and come back to the south. It is believed that the AMO strengthens or weakens the process, resulting in a "conveyor" is accelerated, then slowed down. Since the distribution of cold and warm water on the surface changes, AMO can also affect the regional and global climate (in the same way as does Southern Oscillation in the Pacific).
|The surface temperature of the North Atlantic in September 2001 (image Ronald Vogel, SAIC for NASA GSFC).|
AMO extensively studied, but the questions remain. This is partly due to the fact that in contrast to the El Niño and La Nini her cycle takes much longer, and so on record failed to accumulate enough data. Study Paleoclimatology markers showed that AMO changes over time — sometimes it takes about 60 years, and sometimes fit into twenty.
The authors of the new article offers an interesting way to increase the data set due to a deeper penetration into the past — to 1659, when the Central England began systematic observations of temperature due to the invention of the sealed liquid thermometer. Of course, these observations are regional, not global in nature. But comparing them with measurements of global temperature, going back to 1850, Ka-Kit Tung and Tszyansun Zhou of the University of Washington (USA) concluded that the testimony of Central England very well agree with them.
It turned out that, as a rule, AMO held from 50 to 80 years and, apparently, has taken part in all the major climate shifts of the last 400 years. Little Ice Age XVI-XIX centuries. was probably caused by the decline in the amount of solar energy and a number of major volcanic eruptions, but the researchers believe helped prolong AMO first cold snap, and then — the end.
Experts attribute most of the warming in the first half of XX century. with AMO, leaving anthropogenic greenhouse gas emissions and an increase in solar activity supporting role. In the same way they explain the cooling in the 1960s, and partly — warming in the 1990s. In fact, removing the calculated contribution of AMO, the authors concluded that around 1910 anthropogenic warming was relatively linear — about 0,08 ° C per decade. This is about half the size of the estimates obtained by those who have tried to isolate the contribution of natural variability in warming the past 30 years (for which data are available satellite observations).
Tom Deluort from the National Oceanic and Atmospheric Administration (USA), is also an expert on AMO, strongly doubts the findings of colleagues. Of course, first of all, a question for the legitimacy of using historical records of central England as an indicator of global temperature. For example, because AMO warming in the North Atlantic may come back to haunt the cooling in the Southern Ocean, and they cancel each other out. Moreover, the exact contribution of AMO in global temperature — the occupation is very ungrateful, because the phenomenon itself is not fully explored and understood.
The study is published in the journal Proceedings of the National Academy of Sciences.
Prepared according to Ars Technica.