Climate change alarmists point to the past several decades of European weather to reinforce their claim that global warming has the continent in its grip. A new report shows that this recent warm spell is nothing abnormal or unprecedented—during the 1990s there was simply a return to conditions present during 1931-1960. The reason for the shift is warm ocean temperatures that are, in turn driven by variation in warm ocean currents from the tropics.
The instrumental record shows that, relative to the average temperature of the rest of the world’s oceans, the temperature of the North Atlantic Ocean has fluctuated between anomalously warm and anomalously cool phases, each lasting several decades at a time. Palaeoclimate records suggest that similar variations extend much farther back in time. The observed pattern of multidecadal variation in North Atlantic sea surface temperatures (SSTs) has become known as the Atlantic Multidecadal Oscillation (AMO).
Climate change happens in cycles both long and short. The most dramatic long cycle that humans have experienced is the alternating ice age phenomenon of glacial and interglacial periods. Over the past 800,000 years or so, the world freezes for 100,000 years and then suddenly thaws for 15-25,000 years. Among the best known short cycles are the alternating El Niño/La Niña conditions in the Pacific, which gets blamed for bad weather in North America and failed monsoons in Asia. There are, however, a number of intermediate cycles that function on scales of decades to hundreds of years.
Such cycles are problematic for climate scientists—it is very difficult to tell the difference between a cyclic swing and a human influenced change. It is very easy to observe a rise in temperature that waxes and wanes over a period of half a century and mistake that for something caused by human activity. A new Nature report, “Atlantic Ocean influence on a shift in European climate in the 1990s,” by Rowan T. Sutton and Buwen Dong, takes a look at one such intermediate length cycle that has been confusing climate scientists in Europe for decades. Here is the abstract:
European climate exhibits variability on a wide range of timescales. Understanding the nature and drivers of this variability is an essential step in developing robust climate predictions and risk assessments. The Atlantic Ocean has been suggested as an important driver of variability in European climate on decadal timescales, but the importance of this influence in recent decades has been unclear, partly because of difficulties in separating the influence of the Atlantic Ocean from other contributions, for example, from the tropical Pacific Ocean and the stratosphere. Here we analyse four data sets derived from observations to show that, during the 1990s, there was a substantial shift in European climate towards a pattern characterized by anomalously wet summers in northern Europe, and hot, dry, summers in southern Europe, with related shifts in spring and autumn. These changes in climate coincided with a substantial warming of the North Atlantic Ocean, towards a state last seen in the 1950s. The patterns of European climate change in the 1990s are consistent with earlier changes attributed to the influence of the North Atlantic Ocean and provide compelling evidence that the Atlantic Ocean was the key driver. Our results suggest that the recent pattern of anomalies in European climate will persist as long as the North Atlantic Ocean remains anomalously warm.
The key phrase here is “last seen in the 1950s.” A careful review of historical data reveals that what has happened in Europe over the past couple of decades has happened before—more than half a century before.