Tibetan Plateau Shows Warming Slowdown

Posted by on Nov 17, 2016

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From 2001 to 2014, climate scientists observed a “hiatus” or pause in global warming. It is an issue that has led to much discussion in the scientific community and among climate skeptics who see the trend as an indication that global warming does not exist. According to a paper published by Fyfe et al., the word “hiatus” is not fully accurate. Instead, instrument data shows a slowdown or deceleration (as opposed to a full halt) of global warming at the beginning of the 21st century. Glaciers are key in helping us understanding the global warming slowdown.

In a recent article, Wenling An et al. describe how the glaciers of the Tibetan Plateau show evidence of the recent warming slowdown. Known as the “Roof of the World,” the Tibetan Plateau spans 1,565,000 square kilometers and is the origin of the Indus, Mekong, and Yangtze Rivers. Due to its large size and location near the tropics, the plateau is one of the most ecologically diverse alpine regions in the world. Therefore, the Tibetan Plateau’s response to climate change has been studied extensively, with researchers relying on both meteorological and paleoclimate data.

Most studies to date have taken place in the more accessible eastern and central parts of the Tibetan Plateau, where there are a greater number of meteorological stations. Meanwhile, the northwestern part of the plateau remains remote and formidable. Thus, data gathered in the northwestern plateau continues to be sparse and collected during shorter timeframes. But the northwestern area has an important connection to the Asian monsoon season and mid-latitudes, recently prompting scientists to focus increased attention on gathering higher resolution data from the area. For one, the Tibetan Plateau plays an important role in the Asian monsoon season by acting as a heat source in the summer and a heat sink in the winter, according to an article by Hongxu Zhao and G.W.K. Moore.

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A view of the Tibetan Plateau during the spring (Source: Andrew and Annemarie/Creative Commons).

Interestingly, the new data collected by An et al. revealed that the eastern and northwestern parts of the plateau have experienced entirely different temperature trends since the beginning of the 21st century. The eastern part shows increased warming during that period, while the northwestern part shows no warming.

In their research, An et al. describe the usefulness of using ice cores (drilled samples of ice from a glacier) to detect this phenomena in climate data. For example, ratios of stable isotopes (forms of the same element with a different number of neutrons) found in ice cores provide information that informs us about past climate conditions.

Studies were done on ice cores taken from the Tibetan Plateau examining the relationship of a particular variation of the amount of an oxygen isotope (δ18O) with precipitation and air temperature. The precipitation on the plateau was captured within the ice core as snow, which then converted to ice. The data demonstrated a positive correlation. This means the higher the concentration of δ18O, the higher the temperature of the air when the water evaporated.

In situations of higher δ18O, the research indicates that the air temperature was higher at the time the snow formed. Aside from temperature, the effect of seasonality and the precipitation amount were also examined to understand the relationship of the δ18O concentrations. Through statistical t-tests, An et al. concluded that seasonality and the precipitation amount did not have an effect on the concentration as temperature does. The results indicate that the temperature is the factor influencing the concentration of δ18O, rather than other factors.

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An aerial view of the Tibetan Plateau (Source: NASA/Creative Commons).

The authors of the study drilled ice cores at Chongce Glacier on the northwestern part of the Tibetan Plateau. They looked at samples approximately 60m long and 6000m above sea level, focusing on the δ18O in the ice cores. The team’s conclusions were consistent with other studies of the area, showing that the levels of the isotope increased significantly in the 1990s, and remained high until 2008, when the δ18O levels started to show a steep decline in concentration from 2009 to 2012. This demonstrates that temperature increased significantly until 2008, when the increases in temperature slowed. This research matches two other ice cores taken from the area, as well as instrument data, demonstrating that the Chongce ice cores provide accurate information about past climate. This data further matches global trends.

Temperature has the largest effect on regulating the state of the Tibetan Plateau. As temperatures increase, melting of the glaciers on the plateau increases. The state of the glaciers on the northwestern part of the plateau has been largely stable since the beginning of the 21st century, likely due to slowed warming in the area. Tibetan Plateau glaciers tell us a lot about the pace of global warming and will continue to be a key tool in understanding how the Earth responds to changes in temperature.

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