by A. Watts, Sep 28, 2020 in WUWT
From the GWPF and the better late than never department: (the paper was published in late 2019 but seems pretty solid, using Oxygen18 isotope analysis) – Anthony
A new analysis of global air temperature by researchers from Tongji University in Shanghai has cast light on the much debated recent hiatus in global temperature.
Writing in the Journal of Earth Science the Chinese scientists say there was a rapid rise in global mean surface air temperature after the late 1970s but that this stalled and there was a relative stagnation and even slight cooling that lasted for about 15 years (1998–2012). They add that even though the slowdown was acknowledged by the Intergovernmental Panel on Climate Change Fifth Assessment Report (IPCC AR5) and termed as a hiatus (IPCC, 2013) there was a debate in the scientific community about whether there was a hiatus in global warming or not.
The researchers believe that the debate about the global warming hiatus poses a substantial challenge to our understanding of the global climate response to anthropogenic greenhouse gas emissions and natural variability. They say that the disagreements about the recent global warming hiatus mainly arise from different sources, among which differences across observational SAT datasets may be a key contributor to the contradictory conclusions. So they use an alternative set of data.
They use the ratio of two oxygen isotopes in precipitation, oxygen 16 and 18, which is a proxy for the temperature of precipitation and surface temperature. They are particularly interested in what they term a “robust correlation” between precipitation oxygen ratios and surface temperature over mid- and high-latitude regions. Twelve stations were selected of which ten are located in Europe, and the remaining two in Antarctica and North America, respectively. Using the data they constructed a composite isotope index spanning 1970–2016 by combining twelve precipitation oxygen isotope records collected over mid and high-latitude continents. With it they evaluate the recent global warming hiatus.
Global mean surface air temperature (SAT) has remained relative stagnant since the late 1990s, a phenomenon known as global warming hiatus. Despite widespread concern and discussion, there is still an open question about whether this hiatus exists, partly due to the biases in observations. The stable isotopic composition of precipitation in mid- and high-latitude continents closely tracks change of the air temperature, providing an alternative to evaluate global warming hiatus. Here we use the long-term precipitation δ18O records available to investigate changes in SAT over the period 1970–2016. The results reveal slight decline in δ18O anomaly from 1998 to 2012, with a slope of −0.000 4‰ decade−1 which is significantly different from that of pre-1998 interval This downward δ18O anomaly trend suggests a slight cooling for about −0.001 oC decade−1, corroborating the recent hiatus in global warming. Our work provides new evidence for recent global warming hiatus and highlights the potential of utilizing precipitation isotope for tracking climate changes.