After much of the U.S. experienced an unusually long and cold winter, many ask whether climate change is still happening. There has, in fact, been little change in global mean annual temperature since the early 2000s leaving scientists struggling to figure out where the heat associated with continuing greenhouse gas emissions has gone. In a recent paper, Matthew England and others are the latest to argue that the answer may be “into the Pacific Ocean.”
To understand this process, it may help to think about global climate as a complex system rather than a simple “mean annual temperature,” as is often done. The climate system is fantastically complicated, involving the chemical composition of the atmosphere, the formation of clouds, winds, ocean currents, and other factors. “Global warming” does not mean that you should expect the thermometer in your yard to steadily rise. Instead, “global warming” (or “climate change” as many scientists prefer) refers to the total energy of the entire climate system and all the associated changes.
This study revealed that the ‘trade winds’ over the equatorial Pacific have strengthened over the last decade, causing more mixing of surface waters and altering ocean circulation. This seems to have led to a cooler tropical Pacific, which has reduced global average surface temperature (of about 0.1o C) below what was expected. Interestingly, there is a ~5 year delay of the impact of the accelerated winds on global surface temperatures. The ocean is big, and it takes time for it to mix and slosh. A scary implication is that when the hiatus reaches its inevitable end, global surface temperatures are likely to warm rapidly.
England, Matthew H., Shayne McGregor, Paul Spence, Gerald A. Meehl, Axel Timmermann, Wenju Cai, Alex Sen Gupta, Michael J. McPhaden, Ariaan Purich, and Agus Santoso. 2014. “Recent Intensification of Wind-Driven Circulation in the Pacific and the Ongoing Warming Hiatus.” Nature Climate Change 4 (3): 222–27. doi:10.1038/nclimate2106.
Recent global-warming hiatus tied to equatorial Pacific surface cooling. Yu Kosaka1 & Shang-Ping Xie1,2,3