The Post-1998 Hiatus
Image Source: Gan et al., 2019
North America (180-0°N, 15-60°N) has been characterized as a “major cooling center” by the authors of a new paper (Gan et al., 2019) published in Earth and Space Science.
The continent warmed from 1982-1998, but a cooling trend since 1998 has nearly wiped out all the previous warming.
Overall, there has been no significant temperature change in North America since 1982.
The warming and cooling trends, especially the daily temperature minimum (Tmin), are well-correlated (r=0.71) with the path of the Atlantic Multidecadal Oscillation (AMO) during 1950-2014, leading the authors to conclude that the temperature trends over this 32-year period are “a result of” natural changes in the AMO.
The Key Role of Atlantic Multidecadal Oscillation
in Minimum Temperature Over North America
During Global Warming Slowdown
“Daily Minimum temperature (Tmin) is an important variable in both global and regional climate changes, and its variability can greatly affect the ecological system. In the early 21st century, warming slowdown is seen over the North Hemisphere and North America is one of the major cooling centers.”
“In this study, we found that Tmin experienced an obvious decline in North America during warming slowdown period. Such Tmin decline is closely related to the Atlantic Multidecadal Oscillation (AMO), the correlation between the decadal components of Tmin and AMO reached 0.71 during 1950-2014.”
“According to composite analysis, the AMO on the positive (negative) phase takes two low-pressure (high-pressure) systems in the northeastern Pacific and the North Atlantic at night, accompanied by cyclonic (anticyclonic) circulations and warm (cold) advection in North America. Therefore, the analyses conclude that the Tmin decline during warming slowdown period is a result of the synchronous decrease of the AMO. The results emphasize the key role of AMO on the decadal variation of Tmin in North America.”
Image Source: Gan et al., 2019
Another new paper renews the global warming “hiatus” debate and documents a 21st century cooling trend in northern China that also effectively snuffs out the previous decades of warming for the region.
Satellite-based regional warming
hiatus in China and its implication
“Global warming ‘stalled’ or ‘paused’ for the period 1998–2012, as claimed by the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5) (IPCC, 2013). However, the early drafts of IPCC AR5 have no detailed explanation for this “hiatus” since 111 of 114 climate models in the CMIP5 earth system model did not verify this phenomenon. … In 2017, after a wave of scientific publications and public debate, the climate models as reported in IPCC remain debates, including definitions of “hiatus” and datasets (Medhaug et al., 2017).”
Image Source: Li et al., 2019
“The slowdown in global warming since 1998, often termed the global warming hiatus. Reconciling the “hiatus” is a main focus in the 2013 climate change conference. Accurately characterizing the spatiotemporal trends in surface air temperature (SAT) is helps to better understand the “hiatus” during the period. This article presents a satellite-based regional warming simulation to diagnose the “hiatus” for 2001–2015 in China. Results show that the rapid warming is mainly in western and southern China, such as Yunnan (mean ± standard deviation: 0.39 ± 0.26 °C (10 yr)−1 ), Tibet (0.22 ± 0.25 °C (10 yr)−1), Taiwan (0.21 ± 0.25 °C (10 yr)−1), and Sichuan (0.19± 0.25 °C (10 yr)−1). On the contrary, there is a cooling trend by 0.29 ± 0.26 °C (10 yr)−1 in northern China during the recent 15 yr, where a warming rate about 0.38 ± 0.11 °C (10 yr)−1 happened for 1960–2000. Overall, satellite simulation shows that the warming rate is reduced to −0.02 °C (10 yr)−1. The changes in underlying surface, Earth’s orbit, solar radiation and atmospheric counter radiation (USEOSRACR) cause China’s temperature rise about 0.02 °C (10 yr)−1. A combination of greenhouse gases (GHGs) and other natural forcing (ONAT, predominately volcanic activity, and atmosphere and ocean circulation) explain another part of temperature trend by approximately −0.04 °C (10 yr)−1. We conclude that there is a regional warming hiatus, a pause or a slowdown in China, and imply that GHGs-induced warming is suppressed by ONAT [other natural forcing] in the early 21st century.”